AIRCRAFT ACCIDENT REPORT
1/92
Air
Accidents
I
nvest
ig
at
i
on
Branch
THE
DEPARTMENT
OF
TRANSPORT
Report on the accident to
BAC
One-Eleven,
G-B
JRT
over Didcot, Oxfordshire
on
10
June
1990
AIRCRAFT ACCIDENT REPORT
1/92
Air Accidents Investigation Branch
Department
of
Transport
Report on the accident to
BAC One-Eleven,
G-B
JRT
over Didcot, Oxfordshire
on
10
June
1990
This investigation was carried
out
in accordance with
The Civil Aviation (Investigation
of
Air Accidents) Regulations
1989
0
Crown copyright
1992
Applications
for
reproduction should be made to
HMSO.
First published 1992.
ISBN
0
11
551099
0
1/90
2/90
3/90
4/90
5/90
119
1
219 1
319 1
1/92
LIST OF RECENT AIRCRAFT ACCIDENT REPORTS ISSUED BY
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BAC One-Eleven, G-BJRT
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May 1990
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September 1990
October 1990
February 1991
August 1991
October 1991
December 199 1
April 1992
These Reports are available from
HMSO
Bookshops and Accredited Agents
Department
of
Transport
Air Accidents Investigation Branch
Royal Aerospace Establishment
Farn borough
Hants
GU14
6TD
February
1992
The
Right Honourable Malcolm Rifkiind
Secretary
of
State
for
Transport
Sir,
I
have the honour
to
submit the report by
Mr
D
F
King,
an
Inspector
of
Air Accidents,
on
the
circumstances
of
the accident to British Airways BAC One-Eleven, G-BJRT, that occurred
over Didcot, Oxfordshire
on
10
June
1990.
I
have the honour
to
be
Sir
Your obedient servant
K
P
R
Smart
Chief Inspector
of
Air Accidents
Contents (cont.)
5
APPENDICES
Appendix A
-
ATC Transcript
Appendix
B
-
Layout
of
Birmingham
Aqort
Appendix
C
-
Shift Patterns
Appendix
D
-
Product Sample Check
List
Appendix
E
-
Comparison
of
bolt heads
in
countersinks
Appendix
F
-
Report by the
Behavoural
Psychologist
GLOSSARY
OF
ABBREVIATIONS USED IN THIS REPORT
AAIB
AGS
ASR
ATC
ATSSD
BAC
BCAR
T
CAA
CATC
csc
CVR
DME
DV
FL
FOI
HF
hrs
IAS
IPC
kg
kt
LATCC
lbf
in
LWTR
"M
MATS
MCP
MHZ
NATS
psi
QMDR
QMP
QNH
QRH
RAF
RAE
TIME
UFDR
UNC
UNF
UTC
VHF
VOR
Air
Accidents Investigation Branch
Aircraft General Spares
Air Safety Report
Air
Traffic Control
Air
Traffic Services Standards Department
British Aircraft Corporation
British Civil Airworthiness Requirements
Degrees Celsius
Civil Aviation Authority
College of Air Traffic Control
Chief Sector Controller
Cockpit Voice Recorder
Distance Measuring Equipment
Direct Vision
Flight Level
Flight Operations Inspectorate
High Frequency
Hours
Indicated
Air
Speed
Illustrated
Parts
Catalogue
Kilogram(s)
Knot(s)
London Air Traffic Control Centre
Pound force inch(es)
Licence Without Type Rating
Degrees Magnetic
Manual of
Air
Traffic Services
Maintenance Control Programme
megahertz
National
Air
Traffic Services
pounds
per
square inch
Quality Monitoring Deficiency Report
Quality Monitoring Procedures
Corrected Mean Sea Level Pressure
Quick Reference Handbook
Royal Air Force
Royal Aerospace Establishment
Total Inventory Management for Engineers
Universal Flight Data Recorder
Unified Coarse
Unified Fine
Coordinated Universal Time
Very
High
Frequency
VHF
Omnidirectional Radio Range
Air Accidents Investigation Branch
Aircraft Accident Report
No.
1/92
(E
W/C
1165)
Registered Owner and Operator:
British Airways Plc
Aircraft: Type: BAC One-Eleven
Aircraft Model: Series
528FL
Nationality: British
Registration:
G-B JRT
Place of accident:
Over Didcot, Oxfordshire
Latitude:
54"
34'
North
Longitude:
001" 10'
West
Date and Time:
10
June 1990 at
0733
hrs
All times in this report are UTC
Synopsis
The accident was notified by Southampton Airport Air Traffic Control
to
the Department of
Transport on Sunday
10
June 1990 and the Air Accidents Investigation Branch (AAIB) began
an investigation the same day. The following participated in the investigation:
Mr
D
F
King, Principal Inspector of Air Accidents (Engineering)
-
Investigator in Charge
Mr
R St J Whidborne, Senior Inspector
of
Air Accidents (Operations)
-
Operations
Mr
S
R Culling, Senior Inspector of
Air
Accidents (Engineering)
-
Engineering
Mr
R J Vance, Senior Inspector of Air Accidents (Engineering)
-
Flight Recorders
The investigation was assisted by:
Mr
I
J Weston,
Air
Traffic Control (ATC) Investigations,
Safety Regulation Group,
Civil
Aviation Authority (CAA)
-
ATC
Dr
A J
F
MacMillan
)
Royal
Air
Force
(RAF)
Institute
of
-
Rapid Decompression
Mr
R Green
)
AviationMedicine
-
Human Factors
The accident happened when the aircraft was climbing through
17,300
feet on departure from
Birmingham International Airport en route for Malaga, Spain. The left windscreen, which had
been replaced prior to the flight, was blown out under effects of the cabin pressure when it
overcame the retention
of
the securing bolts,
84
of which, out of a total of
90,
were
of
smaller
than specified diameter. The commander was sucked halfway out of the windscreen aperture
and was restrained by cabin crew whilst the co-pilot flew the aircraft
to
a safe landing at
Southampton Airport.
The following factors contributed to the loss of the windscreen:-
A safety critical task, not identified as a 'Vital Point', was undertaken by one
individual who also carried total responsibility for the quality achieved and the
installation was not tested until the aircraft was airborne on a passenger carrying
flight.
The Shift Maintenance Manager's potential to achieve quality in the windscreen
fitting process was eroded by his inadequate care, poor trade practices, failure to
adhere
to
company standards and use of unsuitable equipment, which were
judged symptomatic of a longer term failure by him
to
observe the promulgated
procedures.
The British Airways local management, Product Samples and Quality Audits had
not detected the existence of inadequate standards employed by the Shift
Maintenance Manager because they did not monitor directly the working practices
of Shift Maintenance Managers.
Eight Safety Recommendations were made during the course of the investigation.
1
1.1
Factual Information
History
of
the flight
The accident occurred during a scheduled flight (BA 5390) from Birmingham
to
Malaga, Spain. With 81 passengers, four cabin crew and two flight crew the
aircraft took off from Birmingham International Airport at 0720 hrs and, having
been transferred by ATC to the Daventry and then the Bristol Sector Controller
of
London Air Traffic Control Centre (LATCC), was cleared to Flight Level
(FL)
140.
A
number
of
radar
headings
were
ordered until the flight
was
instructed
to
maintain
a
radar
heading of 195'M and cleared for a further climb to
FL
230. The
co-pilot had been the handling pilot during the take-off and, once established in
the climb,
the
commander was handling the aircraft
in
accordance with the
operator's normal operating procedures. At this stage both pilots had released
their shoulder harness, using the release bar on the buckle, and the commander
had loosened his lap-strap.
At 0733 hrs as the cabin staff prepared to serve a meal and
drinks,
and, as the
aircraft was climbing through about 17,300 feet pressure altitude, there was a
loud bang and the fuselage filled with condensation mist.
It
was at once apparent
to
the cabin crew that
an
explosive decompression had occurred. The commander
had been partially sucked
out
of his windscreen aperture and the flight deck door
had been blown onto the flight deck where it lay across the radio and navigation
console. The
No
3 steward, who had been working on
the
cabin side of the
door, rushed onto the flight deck and grasped the commander round his waist
to
hold onto him. The purser meanwhile removed the debris of the door and stowed
it
in
the
forward toilet. The other two cabin staff instructed the passengers
to
fasten their seat belts, reassured them and took up their emergency positions.
The co-pilot immediately attempted to control the aircraft and, once he had
regained control, initiated a rapid descent to
FL110.
He re-engaged the autopilot
which had become disconnected by displacement
of
the control column during the
commander's partial egress and made a distress call on the frequency in use but
he was unable to hear
its
acknowledgment due
to
the noise of rushing
air
on the
flight deck. There was some delay
in
establishing two-way communications and
consequently
the
Bristol Sector Controller was not immediately aware of
the
nature of the emergency. This
led
indirectly
to
the LATCC Watch Supervisor not
advising the aircraft operator of the incident, as required by the Manual of Air
Traffic Services (MATS) part
1.
Consequently the initiation of
the
British
Airways Emergency Procedure Information Centre plan was delayed. Meanwhile
the purser re-entered the flight deck and, having hooked his
arm
through the seat
belts
of
the fourth crew member jump seat which was located behind the left-hand
pilot's seat, was able
to
assist the
No
3
steward
in
the restraint
of
the commander.
1.2
1.3
The two men tied to pull the commander back within the aircraft and, although
they could
see
his head and torso through the left
Direct
Vision @V) window,
the
effect of the slipstream frustrated their efforts. The
No
2
steward entered
the
flight deck and
he
was able to relieve the
No
3
steward whose
arms
were losing
their strength as they suffered from frostbite and bruising from the windscreen
frame. The
No
2
steward grasped the commander's right leg, which was stuck
between the cockpit coaming and the control column whilst his left leg was
wedged against his seat cushion. The steward
then
strapped himself
into
the left
jump seat and was able to grasp both of the commander's legs but not before he
had moved a further
6
to
8
inches out
of
the window frame. He held him by the
ankles until after
the
aircraft had landed.
Meanwhile, the aircraft had descended to
FLlOO
and slowed to about
150
knots(kt). The co-pilot had requested radar vectors to the nearest airport and had
been turned towards Southampton Airport and eventually transferred to their
approach frequency. Having verified that there was sufficient runway length
available for a landing, the co-pilot manoeuvred the aircraft onto a visual final
approach to runway
02
and completed a successful landing and stop on the
runway at
0755
hrs.
The engines were shut down but the Auxiliary Power Unit,
which the co-pilot had started up during the descent, was left running
to
provide
electrical power to certain aircraft systems.
As
soon as the
aircraft
came
to
a halt,
passengers were disembarked from the front and rear airstairs while the airport
and local
fire
services recovered the commander back into the aircraft from his
position half out of the windscreen frame, where he had remained throughout the
descent and landing.
He
was taken to Southampton General Hospital suffering
from bone fractures in his right
arm
and wrist, a broken left thumb, bruising,
frostbite and shock. The other crew members and passengers were medically
examined but apart from one steward who
had
cuts and bruising to his
arm
there
were no other injuries.
Injuries to persons
Injuries Crew
Fatal
-
Serious
1
Minor/none
1
Damage to aircraft
Passengers
Others
- -
-
-
- -
The pilot's windscreen was missing and one securing bolt was found
in
the
window frame, this had retained a portion
of
the rubber seal and a metal bush
from
the
windscreen. The bolt was not new and its countersunk head had pulled
through the windscreen. The aircraft window frame was checked for distortion
and found
to
be
satisfactory.
Other
damage
to
the aircraft consisted
oE-
The High Frequency
(HF)
aerial, stretching from a forward position on the top of
the fuselage to a fitting close to the tailplane bullet, was missing and the fittings
damaged. There was a dent on the top left side of the fuselage approximately
3
inches long about
3
feet above the overwing emergency exit and a scratch
on
the top left side
of
the fuselage. Minor damage to several items on the flight deck.
1.4
Other damage
There was no other damage.
1.5 Personnel information
I
S.1
Commander:
Licence:
Instrument rating:
Route check
Safety procedures:
Medical:
I
S.2
Flying experience:
Total:
ontype:
Last 28 days:
Last 90 days:
Co-pilot:
Licence:
Instrument rating:
Route check
Safety procedures:
Medid
Flying experience:
Total:
on
type:
Male, aged 42 years
Airline Transport Pilot's Licence
valid until 13 November
1999
valid until
16
January 1991
valid
until
30
September
1990
last check 23 October 1989
last examination 14 March
1990
Class One,
no limitations
Height
:
1.67 metres. Weight: 70 kg
11,050
hours
1,075 hours
19
hours
96 hours
Male, aged 39 years
Airline Transport Pilot's Licence
valid to 24 June
199
1
valid until
19
November
1990
valid until
8
July 1990
last check
9
October 1989
last examination 20 December 1989, Class One,
no limitations
7,500 hours
1,100
hours
Last 28 days:
Last
90
days:
1
S.3
Cabin
crew:
58 hours
169 hours
Purser: Male, aged 37 years
Male, aged 29 years
No 2:
Male, aged
36
years
No 3:
Female, aged 33 years
No 4:
All Safety and Emergency procedure checks had been completed
in
the current
year.
1.6
Aircraft information
1.6.1
General information
Manufacturer:
Type:
Registration:
Serial number:
Date of manufacture:
Registered owner:
Total
airframe hours:
Certificate of Airworthiness:
Hours
to next check:
British Aircraft Corporation (BAC) Limited
BAC One-Eleven Series 528FL
BAC 234
1977
British Airways Plc
37,724.07 hours
Transport Category (Passenger) expires
16 March 1992
41 hours
G-B JRT
I
.6.2
AircraJt weight and centre
of
gravity
Maximum Take-off Weight Authorised:
Dry
Operating Weight
:
Zero
Fuel Weight:
Payload:
Take-off fuel:
Actual Take-off weight:
Maximum landing weight:
Actual landing weight
(1):
440oo
kg
25,818 kg
32,925 kg
7,107 kg
9,980 kg
42,905 kg
39,460 kg
40,725 kg
Note:
1
Fuel state on landing at
Southampton
was 7,800
kg,
therefore fuel
used during the flight was 2,180
kg.
I
.6.3
General description
1.7
I
.7.1
1.7.2
1.8
1.9
I
.9.1
The BAC One-Eleven 500 series is a twin-engined, passenger aircraft powered by
Rolls Royce Spey turbofans. The fuselage is pressurised and air-conditioned;
8,000 feet conditions being obtainable at 35,000 feet, under which conditions the
pressure differential is 7.5 psi.
The pilots' windscreens are
of
five-ply glass/polyvinyl-butyl construction, the
innermost (glass) laminate being low-tempered
to
form a splinter shield in the
event of a bird strike. Windscreen heating is applied, primarily to improve the
impact resistance of the windscreen at low outside air temperatures. The
windscreen is not designed on the 'plug' principal, where cabin pressure
effectively contributes
to
holding
it
in place, but is fitted from the outside
of
the
aircraft and is secured by means
of
90
countersunk bolts, also fitted from the
outside. The large number of bolts
are
required
to prevent leakage of pressurised
air through the window seal but the force
of
internal air pressure could be
satisfactorily resisted by
far
fewer bolts.
Meteorological information
Synoptic situation
High pressure existed
to
the west of Ireland with a light northerly flow over the
Didcot area. There was a possibility of broken Stratus with a base at
600
feet and
scattered Altocumulus with base at
12,000
feet and tops at 15,000 feet with a thin
layer of Cirrus above 25,000 feet. Visibility was about
10
kilometres. At
18,OOO
feet the wind was 360' at 17 kt and the
air
temperature was minus 17
"C.
The
freezing level was at
9,OOO
feet.
Actual conditions at Southampton
The 0720
hrs
observation at Southampton Airport included the following:-
Wind: 350'/12
kt.
Visibility:-
8,000
metres in haze. Temperature:- plus
15
"C.
Aids to navigation
Not
relevant.
Communications
ATC assistance
At the time of the accident the flight was receiving an
Air
Traffic Area Radar
Control Service from the Bristol sector of LATCC on a frequency
of
132.80MHz. The flight came under the control
of
Southampton Zone on
1.9.2
frequency
131.00
MHz
at
0744
hrs.
A transcript of ATC recorded transmissions
from the onset of the emergency is reproduced at Appendix A.
The co-pilot made a 'Mayday' call and declared that the aircraft had suffered an
emergency depressurisation and was descending
to
FLlOO
on a heading of
195"M.
The controller acknowledged receipt
of
the 'Mayday' call from BA
5390
but did not attempt to establish if the aircraft could still receive his
communications and, although he alerted his Chief Sector Controller (CSC), took
no further action since he was waiting for further information about the
emergency. He continued to operate the sector as if no emergency existed,
accepting further aircraft onto the frequency with no attempt to off-load traffic or
minimise radiotelephony activity. However, fortunately there was no conflicting
traffic and the CSC had advised the neighbouring sectors
of
the emergency
descent and told the LATCC watch supervisor and the RAF Distress and
Diversion Cell about the emergency call. Just prior
to
the handover to
Southampton, BA
5390
was descended
to
an altitude
of
4,000
feet in error rather
than
FL40
as had been co-ordinated, despite the Bristol Sector Controller
not
being aware of the airfields QNH. This difficulty was resolved when the flight
was transferred
to
the Southampton Zone Controller who had been alerted
to
the
possibility of the aircraft landing there and had taken alerting action following a
telephone call from LATCC.
The co-pilot did not select the special purpose Secondary Surveillance Radar
transponder code
(7700)
to indicate an emergency condition but retained the code
that had been already allocated to the flight. This accorded with the United
Kingdom Aeronautical Information Publication RAC
7-4
which states
:
'....if the
aircraft is already transmitting a code and receiving an air traffic service that code
will normally be retained.'
ATC
handling
of
emergencies
Guidance to controllers on the handling
of
emergency traffic is contained
in
the
MATS Part
1
paragraph
5.1.7
which states:-
'Emergency aircraft
-
Selection
of
controlling agency
On receipt
of
information which indicates that an aircraft
is
in
an
emergency, the controller must decide whether or not
to
transfer the
aircraft
to
another agency. The choice
of
agency will depend upon the
circumstances and no hard and fast rules apply. The following guidance
material will help controllers to
de
this
decision:
Retaining Control
I
.9.3
If the controller can offer immediate assistance the aircraft should
normally be retained
on
the frequency. If necessary impose a radio
silence on other aircraft
or
transfer them
to
another frequency.
Alternatively it may
be
more expedient
to
transfer the emergency aircraft
to
a discrete frequency, particularly if a radio silence would endanger other
traffic.
The aircraft will have to be retained on the original frequency
if
it
is
unreasonable
to
ask
the
pilot,
or
if he is not prepared,
to
change
frequency. The controller may be able
to
relay instructions and
information from other units
to
the pilot.
Transferring Control
If
a controller considers that another unit may be able
to
give more
assistance than he can himself, and in the circumstances it is reasonable to
ask the pilot to change frequency, he shall either;
(a) Consult the Air Traffic Control Centre Supervisor and transfer
the aircraft according
to
his instructions,
or
,.
(b) Alert the nearest suitable unit and transfer the aircraft
to
a
common frequency, giving assistance to that unit as required.
Before transferring aircraft, controllers should obtain sufficient
information from the pilot to be convinced that the aircraft will receive
more assistance from another
unit.
If a change of frequency is desirable
the pilot must be instructed to revert immediately
if
there is
no
reply on the
new frequency. Controllers should then listen out
on
the original
frequency until the aircraft is known
to
be
in
two
way communication.'
ATC
training
An ATC service
in
the United Kingdom may be provided only by a person who
holds an Air Traffic Controller's licence with the appropriate rating made valid at
the ATC unit at which
the
service is to be provided. The Air Navigation Order
authorises the grant
of
licences to persons who demonstrate their knowledge,
experience, competence,
skill
and physical and mental fitness
to
the satisfaction of
the CAA. The CAA publication CAP
160
details the evidence which must be
furnished, the examinations which must
be
passed and other requirements which
must be met before licences, ratings, validations and endorsements are issued.
An applicant for a licence is required
to
demonstrate his
or
her knowledge and
skill by passing examinations at two levels:-
a. Rating. The ability
to
provide a particular type
of
ATC service
(eg
aerodrome control, area control or area radar control).
b.
Validity
of
a Rating. The ability
to
provide an ATC service at a
particular place. This includes the ability
to
operate equipment
(eg
radar)
when
it
is used to provide the service.
The Bristol Sector Controller had completed
an
approved course and examination
for the issue
of
an Area Procedural and Area Radar rating at
the
National Air
Traffic Services (NATS) College
of
Air
Traffic Control (CATC) in May
1985
and
was then posted
to
LATCC for validity training. This was successfully
completed and
led
to the rating being validated
on
the Bristol Sector position.
Prior to the mid
1980's
the
Area Radar rating examination had included an
emergency exercise. Both the CATC and the ATC Licencing Branch informally
agreed that the inclusion
of
an
aircraft emergency during the examination placed
undue emphasis on the emergency and worked against assessing the examinee's
ability to handle routine traffic situations.
In
order
to
overcome this problem,
an
agreement was reached between
the
College and ATC Licensing Branch that the
emergency would
be
removed from the examination but that appropriate training
for such events would continue to be given. The Bristol Sector Controller on
duty at the time of
the
emergency had undertaken his course in
1985
but the
precise content of his course could not be established as the records of courses
conducted at that time were not available.
This situation is believed to have continued until
1988
when the ATC Licensing
Branch was removed from NATS and placed within the CAA Safety Regulation
Group, eventually becoming part of the Air Traffic Services Standards
Department (ATSSD). Due in part to that change, the CATC, which remained
within NATS, was required to submit to
annual
inspections by the ATSSD
so
that
approved courses might continue.
In
contrast to other ATC courses which have a
published syllabus (CAP
390
-
ATC Training Manual) no such publication is
made for Area ProceduraVArea Radar Courses.
As
the CATC was the only
establishment to provide such courses, individual syllabuses were agreed between
ATSSD and the College.
No
mention
of
practical emergency training
is
given in
this syllabus for area radar nor in the course approval which was given after
the
ATSSD inspection in
1989.
The syllabus did require certain parts
of
MATS
Part
1
relating to emergency training
to
be covered, but instructors took a wider
view and also tended to discuss the handling
of
emergency situations during
theoretical lessons. The instructors, however, found it more difficult to
incorporate emergency situations into routine practical exercises as they found it
was likely to disrupt the learning process. Such training tended
to
be injected at a
relatively early stage
of
the course with little opportunity for later consolidation.
Therefore, the course manager was allowed
to
omit certain emergency situations.
As a consequence, training in practical emergencies could be reduced
to
such an
extent that
it
was non-effective. As the syllabus did
not
require practical
emergency instruction, the CATC management did not inform ATSSD where
such training was not given. ATSSD was not aware that such decisions had been
taken and believed the situation remained as per
the
agreement following
the
removal of emergencies from the examination. Once a student leaves the College
there appears
to
be
no requirement to undergo any emergency training
or
periodic
appraisal on emergency procedures in order
to
maintain an Area/Area Radar
validated rating.
1.10
Aerodrome information
The single concrete runway, 02/20, at Southampton Airport is 1,723 metres long.
The landing distance available on runway
02
is 1,650 metres.
A VOR/DME
(SAM
113.35
MHz)
is located
on
the airfield which is at an elevation
of
44
feet
above mean sea level.
1.11
Flight
recorders
1
.I1
.I
Cockpit Voice Recorder (CVR)
A
Fairchild Model A100 four channel CVR was
fitted
and a satisfactory replay
of
the
30
minute audio record was obtained. Channel allocation was
:-
Channel
1
Cabin Address
Channel 2 Co-pilot's hot microphone
Channel
3
Pilot's hot microphone
Channel
4
Cockpit area microphone
The rapid decompression caused no discernible change to the signal on the area
microphone channel but it was clearly audible on both crew hot microphone
channels.
1.11.2
Universal Flight Data Recorder (UFDR)
1.12
A Sundstrand UFDR was fitted. A satisfactory replay was obtained from the
following recorded parameters:- Indicated Airspeed, Altitude, Heading, Normal
acceleration, Flap position, Pitch attitude, Roll attitude, No
1
engine
W,
No 2
engine
W,
VHF
transmit discrete.
Recorded data showed the aircraft climbing at 300 kt Indicated Airspeeed
(US)
through 17,300 feet at the time of the loss of the windscreen. As the control
column was pushed forwards, probably due to the movement
of
the commander
through the windscreen frame, the aircraft pitched
6'
nose down and banked 25'
to
the right. When the co-pilot took control and closed both throttles, the speed
was allowed to increase to 340 kt as
the
aircraft descended at 4,600 feet per
minute to FL110. On reaching this level the speed was reduced
to
266 kt with a
further decrease to 163 kt as flaps were extended according to the normal
operating schedule and then power was applied to maintain this height and speed.
The time elapsed from the depressurisation to level flight at FLllO was 148
seconds.
Wreckage
and
impact information
The aircraft was brought
to
rest on the runway and electrical power turned
off.
The aircraft was towed off the runway and parked.
1.12.1
&minution
of
the
left wi&creen and attaching
bolts
The windscreen was found near Cholsey, Oxfordshire, along with the
windscreen outboard corner post
fairing
strip and some associated bolts.
Of the
90
bolts used
to
attach the windscreen to
the
aircraft,
11
had remained
in
the windscreen and 18 were found loose nearby;
one
had remained in the aircraft
window frame.
Twenty-six of the bolts recovered with the windscreen were new bolts identified
against the British Standard as Raving the part number A21 1-8C. The remaining
four bolts recovered were re-used bolts identified as having the part number
A21
1-7D. The Illustrated Parts Catalogue (IPC) specifies that the attaching bolts
should
be
part number A21 1-8D. The specifications for these bolts are:-
Part No. Shank length (inches) Diameter (inches) Thread Size
A21
1-8D
0.8
0.1865-0.1895
10
UNF
A211-8C
0.8
0.1605-0.1639
8
UNC
A21
1-7D
0.7
0.1865-0.1895
10
UNF
UNF
=
Unified Fine
UNC
=
Unified Coarse
1.13
1.14
1.15
The bolts engage with
10
UNF Kaylock floating anchor nuts mounted on the
inside of the windscreen frame. The replacement windscreen had been installed
with
84
bolts (A21 1-8C) whose diameters were approximately 0.026 of an inch
below the diameters of the specified bolts but of the same thread pitch, and six
bolts (A21 1-7D) which were of the correct diameter, but
0.1
of an inch
too
short.
The left windscreen had been changed during the night shift of the 8/9th June
1990
and
the
accident flight was the first since that installation. Eighty of the
bolts which had attached the old windscreen were recovered from the work area
during the investigation, and 78 of these were identified as A211-7D, the
remaining two being A21 1-8D. The old windscreen, which had been fitted four
years earlier, before the aircraft had been acquired by British Airways, had
therefore been primarily attached by bolts which were
0.1
of an inch shorter than
those specified.
Medical and pathological information
Not relevant.
Fire
There was no fire.
Survival aspects
Following
the
loss of the left windscreen and subsequent decompression of the
fuselage, the commander found himself half way out of the aircraft through his
Windscreen aperture. He recalls the impression of lying
on
his back against the
upper surface of the flight deck exterior and, realising that he was still able to
breathe, he concentrated on this until he assumes he lost consciousness. He
regained consciousness after the aircraft had landed and when he was being
recovered by
fire
and ambulance staff inside the flight deck prior
to
be being
placed
on
a stretcher and taken to hospital.
The co-pilot and the crew members who were holding
on
to
the commander had
individually reached the conclusion that his survival was highly improbable in the
extreme conditions to which
he
was exposed. They were considerably reassured
when, at a late stage in the descent at about
3,000
feet, the commander started
to
kick his legs.
The aircraft was not fitted with an automatic presentation oxygen system
in
the
cabin and this was not required
to
be
fitted
under the
original
requirements for the
issue of the aircraft's Certificate of Airworthiness. Therapeutic oxygen was
available in the cabin and consisted of 18 sets of facemasks and four portable
oxygen cylinders. The oxygen system supplied gaseous oxygen to the crew and
passengers if decompression occurred and
for
therapeutic purposes. Oxygen
cylinders were mounted underfloor
in
the forward fuselage
in
the electrics bay.
From the cylinders the oxygen was piped through in-line filters
to
the control
panel in the flight deck right hand console. For therapeutic supply,
an
outlet from
the double pressure regulator connected
to
an isolation valve (normally closed)
and thence
to
a ring main which served twinflow sockets
in
selected passenger
service panels. With the crew shut off valve and passenger isolation valve open,
oxygen was obtained by connecting a therapeutic mask to an outlet point.
Therapeutic masks were stowed in the aft stowage compartment. Immediately
following the loss
of
pressurisation, the No 2 steward went and sat in seat 20D
whilst donning the mask
of
a portable set that was stowed nearby. Oxygen
masks
were available to the flight deck crew but the co-pilot elected not to don his
mask since
he
realised that the aircraft would soon reach FLlOO (see paragraph
1.17.7 below). He also did not want to impede his ability
to
communicate with
the other crew members who were holding on
to
the commander.
1.16
Tests
and
research
I
.16.1
Trials
of
8
UNC
and
IO
UNF
countersunk
head
bolts
with
10
UNF
anchor
nuts
During the course of the investigation British Airways carried
out
a simulation of
the window fitting procedure to determine the torque that could be applied to
8
UNC countersunk head bolts fitting into
10
UNF Kaylock type anchor nuts. A
24
anchor nut test piece was used as follows:
To determine the torque at thread slip of twenty 8 UNC bolts in
10
UNF
Kaylock
nuts. This was found to be
in
the
range of
1
to 7 lbf in.
To determine the torque required to engage the bolt in the locking mechanism of
the nut, four
10
UNF bolts were fitted in
10
UNF Kaylock nuts. This torque
was found to be in the range of
10
to
11
lbf in.
A further, more representative test was carried out in the presence
of
AAIB
using
a BAC One-Eleven in which
32
bolts (A21 1-8C) were used
to
fasten a window
and seal
in
an aircraft. In this test torque figures ranging between
0
and 12 lbf in
were achieved before the threads slipped.
A
third test was carried
out
using some of the anchor nuts removed from G-BJRT
to ensure that no unforeseen effect could have made the G-BJRT window
unrepresentative; ten
8
UNC
bolts were
fitted
and these slipped at torques ranging
from
0
to
6
lbf in.
The combined results using
8
UNC
bolts
in
10
UNF
Kaylock nuts showed a
maximum torque of
12
lbf
in
and an average
of
4.7
lbf in at thread slip.
It
was noted that the thread range
4
UNC
to
inch
UNF,
commonly used on
aircraft bolts, contains three adjacent pairs of sizes with similar thread pitches
which allow the smaller bolt to engage in the larger Kaylock nut.
1
J6.2
Examination
of
the
torque
limiting
screwdriver used
to
fit
the
windscreen
Tests
on
a similar torque limiting screwdriver to that used
to
fit
the windscreen
showed that at a low setting
(5
lbf in) the feel
of
the screwdriver clutch slipping
was indistinguishable from the feel
of
an
8
UNC
thread slipping
in
a
10
UNF
anchor
nut.
At a higher setting
(15
lbf
in)
a more pronounced click was felt as the
screwdriver clutch released.
The actual torque limiting screwdriver
used
had a high level of residual friction
(typically
7
lbf in at a setting
of
20
lbf in) after
the
set value had been achieved
and was therefore taken to the manufacturer for examination
in
the presence of
AAIB and British Airways. The torque limiting screwdriver employed a cam
plate with three lobes to retain three ball bearings which were displaced against
the action of a spring
to
release at the set torque. Once released, the drive shaft
carrying the ball bearings rotated through a third
of
a revolution until the balls re-
indexed against the cam. Thus, in use, the torque should build up
to
the set
value, slip and reduce
to
a residual value whilst the balls move across the constant
radius section
of
the cam
to
the next indexing position.
The residual torque was confiied as being high at
a
value
of
approximately
30
per cent of the torque set, rather than the usual value
of
between
5
and
10
per
cent. Subsequent discussions with the manufacturer disclosed that the
specification
for
the grease, used in the assembly of the torque limiting
screwdriver, had been changed approximately five years ago because
of
problems
of the grease breaking down with age. At this time retrospective action for those
torque drivers already sold was considered impractical because
of
the large
numbers involved and the lack
of
information about their location. The
screwdriver under test was at least five years old and strip examination revealed
that
the
excessive friction was caused by deterioration of the old specification
grease.
No
significant wear was evident on the cam
or
the ball bearings, and
when rebuilt with
the
correct grease the torque limiting screwdriver performed
satisfactorily.
The high residual torque occurred after the set value had been achieved
(ie
20 lbf
in) and did not affect the torque at which the screwdriver operated. The residual
torque would not have been felt before the set torque was reached.
I
J6.3
Special
checks
called for on widcreen bolts after the accident
Before the diameter
of
the replacement bolts had been established British Airways
issued
an
instruction
to
be carried out on all its BAC One-Elevens before the next
flight, to remove every fourth bolt from the
No
1
left-hand and
No
1
right-hand
windscreens
to
check for correct length.
Throughout
the
British Airways fleet of BAC One-Elevens two aircraft failed the
check, having a total of 41 short bolts
(A21
1-7Ds).
A similar check was carried out on
the
four BAC One-Elevens belonging to
another airline and
two
aircraft
failed
the check, having a
total
of 107 short bolts.
When the smaller diameter bolts were identified in the detached window British
Airways called for a
100
per cent visual inspection
of
bolt
head diameter; this
check utilised the fact that the smaller bolt head had
27
per cent less area than the
head of the correct
bolt.
All
the
aircraft
passed
the
check.
1.17
Additional information
I.17.I
Certijication
of
Airworthiness
of
Aircraft
1.17.1.1
Type
Certification of the BAC One-Eleven
The BAC One-Eleven Model
500
was type certificated
to
British Civil
Airworthiness Requirements (BCAR) Section D in 1970 which calls up duplicate
inspections after certain safety critical maintenance operations. However the
glazing elements of windscreens are not identified as principal structural elements,
nor does the application of this duplicate inspection philosophy attempt
to
cover
possible safety critical situations caused by servicing errors.
There
are
no airworthiness requirements for aircraft windows to be fitted from the
inside (plug type).
The BAC One-Eleven windscreen was designed
to
be secured with countersunk
head bolts to British Standard A21 1-8D. This British Standard specifies that the
British Standard number and
the
bolt part number shall not be applied
on
the
bolts, but shall
be
clearly marked on the labels
of
parcels of bolts.
1
.
1
7.1.2
Aircraft Maintenance Requirements
a. Duplicate Inspections
BCARs
require
a duplicate inspection of
all
control systems in an aircraft to
be made after initial assembly and before the first flight after overhaul,
repair, replacement, modification
or
adjustment. In September 1985
BCARs introduced a requirement for duplicate inspections of 'Vital Points',
which
are
defined as any point on an aircraft at which a single mal-assembly
could lead
to
catastrophe,
Le.
result
in
loss of the aircraft and/or fatalities.
The CAA state that the term 'Vital Point' is not intended to refer
to
multiple
fastened parts of the structure, but only applies
to
a single point, usually in a
control system.
The regulations contain a waiver making the definition of 'Vital Points' non-
mandatory for aircraft with a Maximum Take-off Weight Authorised
of
over
5,700 kg which were manufactured in accordance with a Type Certificate
issued prior
to
1st January 1986. This waiver includes
the
BAC One-
Eleven. However, even had
it
not, British Aerospace would not expect the
pilots' windscreens
to
appear in a 'Vital Point' analysis of
the
BAC One-
Eleven.
b. Cabin Pressure Checks
There are no CAA requirements for a cabin pressure check
to
be called up
after work has been carried
out
on
the
pressure hull. There is no specific
company policy on leak checks within British Aerospace. Such checks are
written into the aircraft Maintenance Manual at the discretion
of
the aircraft
design team, and were not called up on the BAC One-Eleven.
1.17.1.3
Quality
Requirements for Airlines
CAA approval
of
Aeroplane Maintenance Organisations, such as British Airways,
includes a requirement for a company exposition containing details
of
the systems
and procedures for the control of matters, including Quality Control, directly
affecting continuing airworthiness. The systems established for Quality Control
and Quality Assurance should be such that the prime objective is to maintain a
continuous check on the effectiveness of the maintenance organisation and on the
procedures and systems employed to ensure that
all
CAA requirements as well as
those
of
the
Organisation itself are met.
When assessing an Organisation for approval the CAA will examine the systems
used
to
control all maintenance activities, including Quality Control and
Assurance. The certification procedures
used
by many airlines, including British
Airways, and approved by
the
CAA, allow a single authorised engineer to
undertake most aircraft work within his trade boundaries, and sign for
it,
without
supervision or independent checking. The exception to this,
on
the BAC One
-
Eleven, is the requirement for duplicate inspection of control systems.
1.17.1.4 Maintenance Engineer Licencing
Aircraft maintenance licences
are
issued for a period of two years and renewed for
a maximum period of five years. Licences will normally be renewed
on
application provided that, during
the
24
months preceding the date of expiry
of
the licence, the holder has been engaged for periods totalling at least six months
on
appropriate work.
No
medical standards are specified for issue or renewal,
neither are any examinations associated
with
the renewal of licences.
No
periodic
training or tests are required on individual maintenance engineers.
The CAA issue aircraft maintenance engineer's licences
in
several categories, of
which category
'A
applies to aeroplanes. Generally there are two parts to each
category:-
a. Licence Without Type Rating
(LWTR)
The LWTR does not in itself confer any certification responsibilities or
privileges but is a prerequisite for the granting
of
the relevant Type Ratings
which confer the privileges
of
certification appropriate to that Type Rating.
The LWTR is also a prerequisite for issuing an approved company
authorisation in the appropriate licence category.
b. Type Ratings
Type Ratings confer on the holder of a licence privileges and certification
responsibilities in respect
of
certain aircraft registered
in
the United
Kingdom.
1.17.1.5 Company Authorisations
Certain aircraft types may be maintained only by organisations which
are
specifically approved by the CAA for that purpose
-
BCAR chapter A8-13 refers.
Licence Type Ratings are not granted for these types.
In
accordance with the
procedures associated with this CAA approval the organisation may grant
authorisation to persons to issue Certificates
of
Release
to
Service for specific
aircraft types to suitable engineers who hold a
LWTR.
The organisation can also issue such authorisations
to
cover aircraft types for
which a Licence Type Rating is available. British Airways is such an approved
company and the fitting of the windscreen and its certification were in accordance
with these procedures.
The holding of company authorisations allows the engineer
to
make maintenance
certifications affecting the airworthiness of the aircraft.
Therefore, such an
engineer carries some of the responsibility
for
the day-teday airworthiness of the
aircraft.
1.17.1.6 Maintenance Manuals
The CAA requires the BAC One-Eleven
to
be serviced in accordance with the
BAC Maintenance Manual, which contains chapters covering each system
in
the
aircraft, each chapter providing: a detailed description
of
the system and its
operation, with sufficient detail for diagnostic use by the aircraft maintenance
engineers; specific values to be achieved during servicing,
ie
torque loadings,
pressures, dimensional checks, timings, etc; procedural information containing
detailed sequences of the steps
to
be followed during the removal and replacement
of significant items. The Maintenance Manual is complemented by the IPC,
which contains detailed drawings of all parts of the aircraft and identifies the
components used by manufacturers' part numbers.
Although
the
Maintenance Manual breaks the windscreen removalheplacement
task into a series
of
individual steps, the British Airways maintenance
documentation at that time treated the task as a single stage operation.
I
.I
7.2
British Airways' i$rastructure
Paragraphs 1.17.2.1
to
1.17.2.3 contain extracts from a much longer internal
British Airways document.
1.17.2.1
Quality Monitoring Procedure (QMP)
-
The System
British Airways policy is that quality cannot be policed
into
a product. The QMP
system, which was introduced
in
1987, was developed actively
to
pursue a policy
of encouraging staff
to
'wear the mantle
of
Quality Assurance' as they went about
their work tasks. QMP forms the structure on which
all
of the monitoring activity
is based and has three main components, these
are:
The Local Exposition;
Continuous Monitoring; and Product Sampling.
a. The Local Exposition
Each Departmental Head is required to raise a Local Exposition which lists
the functions for which he or she is responsible and the geographic
locations where the work is carried
out.
The functions are allocated to
managers, by name, and the procedures that are used to control tools,
equipment, procedural and documentary amendments, modifications,
special processes, etc. are defined. Each Local Exposition is registered with
the CAA and, in conjunction with other documents, forms the British
Airways' submission for requesting approval for
the
various engineering
functions that
are
carried out.
b. Continuous Monitoring
The second requisite is the availability of a reporting system through which
all staff can register deficiencies as they occur (by raising a Quality
Monitoring Deficiency Report (QMDR)), this is a 'closed loop' system
which informs the originator of
the
action that has been taken
to
rectify the
problem. This is known as Continuous Monitoring.
The QMP system is confined
to
airworthiness related items and does not
duplicate other reporting systems.
It
can, however, report the shortcomings
in other systems where this is appropriate in airworthiness terms.
The role
of
the individual is crucial
to
the success
of
the QMP system. The
QMP system gives each person the responsibility
of
reporting deficiencies
in the quality of the services and procedures which are provided
to
them and
on
which they depend
in
order to produce their
goods
or services at the
proper level of quality. By
so
doing, they are given a formal device for
influencing their working environment.
c. Product Sampling
In
addition
to
the Continuous Monitoring process there is an imposed
Product Sample that has to be carried out at set periods to satisfy the
requirement
of
an independent assessment of work. Product Sampling is
seen as a check on
the
effectiveness of the Continuous Monitoring system
and all sample reports are submitted
to
the Chief Quality Engineer for
evaluation; some of which are passed on to the CAA in support
of
their
approval
of
British Airways' maintenance arrangements.
1.17.2.2
The Management Role
in
QMP
The Departmental Head is responsible for his organisation's quality performance,
for assessing standards and for maintaining a quality awareness in all his staff.
Through the Local Exposition, the Departmental Head declares the
staff,
facilities,
equipment and systems for which he is responsible and sets down how Quality
Monitoring is to be implemented throughout his area of responsibility. He holds
regular briefings to ensure that Continuous Monitoring is being correctly applied,
and monthly summary reports
of
the QMP system
are
submitted to him by his
staff. From this monthly
summary
it
is possible
to
deduce the amount of QMP
activity, in terms
of
numbers of deficiencies raised by Continuous Monitoring and
by Product Sampling.
Every quarter the Departmental Head summarises
all
of
the
QMP activity for his
area by completing a Quarterly Report. The Quarterly Report is sent to the British
Airways Audit Unit who compile statistics from the reports and report those
statistics to the Quality Forum. Forum meetings are arranged monthly and are
chaired by the Chief Engineer
of
Quality and Training Services
on
behalf of
the
Engineering Director. The CAA Surveyors in charge of both the Heathrow and
Gatwick offices participate
in
these meetings.
The Quality Forum ensures that Departmental Heads are accountable for the QMP
process and provides the opportunity for quality objectives and performance
to
be
discussed and acted upon.
1.17.2.3 Auditing theProcess
The effectiveness
of
the QMP is assessed through independent audits which
are
conducted by a small group
of
quality engineers from the Quality Audit Unit, a
paperwork exercise every six months and a visit every two years. In addition
they will act in an advisory capacity on airworthiness matters and on the
management
of
the QMP system. The independence
of
the Audit Unit from the
engineering operation has been accepted by the CAA, who check
on
this aspect
through regular surveys on the Audit Group.
The Audit Unit is also empowered to carry
out
traditional 'systems audits' if
sufficient grounds exist to suspect that functions
or
procedures are not properly
controlled. The results
of
such audits are reported
to
the appropriate Departmental
Head
so
that the necessary corrective action can be taken. As a last resort, the
result can also be reported
to
the Quality Forum, for corrective action to be
allocated.
1.17.2.4 The Maintenance Control Programme
(MCP)
British Airways is approved by the CAA as a maintenance organisation; as part
of
that approval, the MCP has been developed. This is a closed-loop system which
is continuously reviewed by engineering management to ensure that aircraft
technical performance is satisfactory. As part of the programme, the following
performance parameters are measured and monitored:-
Aircraft
technical delays
Aircraft systems performance
Engine in-flight shutdowns
Unscheduled component removals
Repetitive defects
Air/Ground incident reports.
These parameters are analysed, and where appropriate have defined targets or
alert levels. All of these parameters
are
evaluated and reported on for all fleets
and corrective
action
taken through a series of structured MCP committees, which
in
turn report to an Engineering Control Review Board who meets formally twice
per year to review the effectiveness of the MCP.
1.1
7.2.5
Ground Occurrence Report Form E 1022
Ground Occurrence Report Form E1022 is used for the notification
of
defects
found during work on aircraft or aircraft components which
are
considered
worthy
of
special attention. The system is also used
for
the notification of
'Ground Found' Mandatory Occurrence Reports as required by the Air
Navigation Order and Regulations and to highlight any technical
or
other matter
which,
if
unreported, could lead to a potential airworthiness hazard.
All British Airways' Engineering staff are required to take E1022 action when
encountering deficiencies
of
the type listed below, unless the subject
of
an
Air
Safety Report:-
Failure,
potential failure or obstruction
of
any aircraft system
Defects
in
aircraft structure such as cracks in primary or secondary
structure, structural corrosion
or
deformation greater than expected
Failures or damage likely to weaken attachments of major structural items
including flying controls, landing gear, power plants, windows, doors,
galleys, seats and heavy items
of
equipment
When any component part of the aircraft
is
missing, believed to have
become detached in flight
Overheating
of
primary or secondary structure
Unreported damage
Defects that cannot be cured by normal replacements
or
repairs
Incmect assembly
Use of incorrect fuel,
oil
or other vital fluids
Failure of any emergency equipment that would prevent
or
seriously
impair its use
Critical failures
or
malfunction of equipment used
to
test aircraft systems
or
aircraft
units
ActuaVpotential fires
Items rejected ex-stores and low life failures
Lack of clarity or conflict between technical procedures
Spillages in aircraft
Any defects found as a result of a Special Mandatory Inspection
or
Check
Any other occurrence
or
defect considered to require such notification.
I
.I
7.3
British Airways' Organisation at Birmingham
1.17.3.1
Task
The task includes flight servicing, scheduled maintenance and rectification of the
13
BAC One-Eleven fleet, and flight servicing and rectification for other British
Airways aircraft
(HS
748
and ATP) and other contracting airlines. The first batch
of the British Airways One-Eleven fleet depart between
0630
hrs
and
0730
hrs
each weekday morning.
For
operational reasons most of
the
maintenance work on the BAC One-Eleven
fleet was carried out at night and consequently the Shift Maintenance Managers on
the night shift usually had more work available to them than they could satisfy.
This required the allocation of task priorities and the night shift manpower was
usually sufficient to complete all the necessary airworthiness engineering tasks
with only minor Acceptable Deferred Defects being left to be dealt with by a
subsequent night shift. Indeed, in order
to
curb over-enthusiasm engendered by
the pride felt by the shifts in their ability
to
satisfy the task, the management at
Birmingham repeatedly stressed that night shifts should not attempt to
do
more
than was prudent.
1.17.3.2 Facilities
At the time of the accident Birmingham Airport was undergoing extensive works
services
to
increase its capacity. The British Airways engineering facilities
comprised accommodation at
two
locations:-
a. Under the International Pier
Office accommodation plus an unmanned store with an adjacent small
workshop area which contained a carousel with
408
drawers holding
consumable Aircraft General Spares (AGS).
b. Eastern Apron
A hangar bay large enough to contain a BAC One-Eleven, with a tail
dock
containing staging allowing access to the
tail.
The Eastern Apron used to
be
the terminal area and the bay contained accommodation previously used by
the
engineering department. This facility housed a manned store and
.
engineering accommodation suitable for work in the area.
The geographical location of these areas is shown at Appendix B.
1.17.3.3 Manpower
The engineering establishment comprised
:-
a. An Area Maintenance Manager with responsibilities for outstations in
MidSouth England; these included Birmingham, Jersey, Southampton,
Cardiff, East Midlands and Bristol Airports. However Southampton,
Cardiff, East Midlands and Bristol were not served by British Airways
scheduled operations, although British Airways charter flights may have
landed there occasionally. British Airways had no engineering staff at these
stations which were served as necessary by agencies, appointed by the Area
Maintenance Manager, or visiting engineers for specific flights. Jersey was
a transit station with, at most, one aircraft stopping overnight. Therefore
more than
80
per cent of the Area Maintenance Manageis time and attention
was devoted to Birmingham. He was specifically responsible for the
control and effectiveness of the Quality Monitoring system
in
maintaining
the established quality performance targets and was to conduct regular
checks throughout the organisation assigned
to
him
to
ensure that quality
performance targets were achieved.
b. A Station Maintenance Manager of foreman grade, who acted as deputy
to the Area Maintenance Manager.
c.
Five rotating shifts, comprising a Shift Maintenance Manager of foreman
grade and approximately six engineers and a storekeeper.
d. A permanent night shift
of
four engineers
to
supplement the duty night
shift and three double day shifts of three men
to
augment day work.
These figures
are
establishments, manning levels on shifts may be depleted by
leave, sickness, etc.
1.17.3.4
Station Organisation
The Station Maintenance Manager and the Shift Maintenance Managers all
reported directly to the Area Maintenance Manager. The only Terms
of
Reference
that were available for the engineering maintenance personnel employed by
British Airways at Birmingham were those which appeared
in
their Union
agreement, however their job specifications may have appeared in recruitment
advertisements issued locally.
a. Shifts
The shift pattern worked by the five rotating shifts gave
24
hour cover over
a
35
day cycle. The duty shift was augmented by the various standing
shifts in a system designed to provide optimum cover at the times when it is
needed, primarily for aircraft handling during the day and rectification at
night. Reduced cover was provided over the weekends. A diagrammatic
representation of the shift system is shown at Appendix
C.
b. Workload
The workload for
all
levels of management at Birmingham was high; the
Area Manager did not monitor the day-to-day work practices of his
subordinates, but relied on the trending of parameters such as numbers of
Acceptable Deferred Defects, repeated defects, and failures
to
meet
schedules as indicators
of
quality. (The total list of parameters is at
1.17.3.6
b).
Although the Station Maintenance Manager was responsible
for
the technical
activities on the Unit, he was the same grade as, and received the same pay
as,
the
Shift Maintenance Managers under him. He worked on aircraft when the need
arose and
so
was closer to the day-to-day standards used, however the
organisation structure was such that Shift Maintenance Managers often
communicated directly with the Area Maintenance Manager. Because
of
his day
time duties the Station Maintenance Manager rarely had the opportunity
to
observe
the workings of shifts at night, especially during the early hours of the morning.
1.17.3.5
Stores procedures
The stores computer based Total Inventory Management for Engineering
(TIME)
system employed by British Airways is such that an item whose part number has
been identified can be located down to the drawer containing the stock. All parts
and materials are requested by description and part number as specified in the
IPC
which is available at all work stations.
AGS
are contained within a dispenser with a stores identification label and issue
may either be over the counter, or self service. This method
used
to
dispense
AGS
is common throughout airlines. At Birmingham three carousels were
employed,
two
in
the hangar under the control of a storeman, integrated in the
TIME
system, and labelled with drawer location codes, and one, uncontrolled,
under the International Pier with drawers labelled with part numbers.
AGS
generally arrived
in
transparent plastic packs of
100
items, the packs
containing a label or a computer produced description and bar code; the drawers
frequently contained the identifying labels from the packs. There was, however,
no way, other than measurement, of identifying the contents after they had been
removed from the packs.
Minimum stock levels per drawer were usually set at between
50
and
100
items
depending on bulk and usage. The hangar carousels contained drawers with
stock levels well below the resupply level; no instances were found of incorrect
contents
in
the hangar carousels. The uncontrolled carousel,
on
the other hand,
had some drawers which were not labelled and some which contained a mixture
of items. The
408
drawers
in
this carousel were categorised as follows:-
No
label, no contents
46
No
label, contained stock
25
Labelled, no contents
68
Labelled, contained stock
269
The last category was further broken down showing that:-
In
25
1
drawers the majority
of
the contents were as the label,
(163
drawers
contained solely the contents described on the drawer label).
In
18
drawers the majority of the stock was wrongly labelled, (in
9
drawers
none of the contents were as described on the drawer label).
The uncontrolled nature
of
this carousel had been recognised by some British
Airways personnel, who had reported the problem informally. There was no
record of this problem
in
the QMDRs at Birmingham, a system specifically
designed to receive reports of this nature.
1.17.3.6
Quality AssurancePractice
a.
Training
The initial training for
QMP
consisted of
1
1/2
days of external training for middle
management who provided
ad
hoc training
to
foremen and supervisors
in
the local
area, based on a standard package consisting of a video plus viewfoils. The
foremen in turn were required
to
train the subordinate grades.
Continuation training in QMP was carried out as and when required. The Audit
Team, through sampling
of
QMP awareness across the Company
in
June 1988,
identified a shortfall; the Quality Forum directed each Department
to
carry
out
QMP training, and an illustrated ‘Guide
to
QMP’
was produced. A further
QMP
survey in January 1989 identified that improvements had been achieved but that a
lack
of
comprehension still existed. At the time of the accident, action
to
remedy
this was still under discussion.
b. The Birmingham Exposition
Product Samples were required from Birmingham on a monthly basis and prior to
each aircraft Certificate
of
Airworthiness renewal. They were carried out by the
Station Maintenance Manager and a nominated Shift Maintenance Manager. The
quality monitoring schedule for the Product Sample is at Appendix D.
The completed Product Sample proforma were distributed to the Area
Maintenance Manager, the British Airways Quality Forum and some to the CAA.
A British Airways Engineering Department procedure stated that the Area
Maintenance Managers were responsible for maintaining the established quality
targets with respect to the following:-
Technical Despatch Reliability
Acceptable Deferred Defect levels
Repetitive Defects
Air Safety Reports
Significant Technical
Defects
sent for investigation (E1022’s)
Product Samples
QMDRs
Quality Audit Reports
Technical
Log
entries.
c. Continuous Monitoring Reports from Birmingham
British Airways literature circulated amongst engineering staff stressed the need
for
an
open reporting system using QMDRs. Over a
39
month period, ending
in
April
1990,36
QMDRs were raised on local issues at Birmingham. Eleven of
these were as a result of the monthly Product Samples, and the other
25
were
raised by the British Airways employees, of whom approximately a quarter had
been active in the system.
The
Area Maintenance Manager stated that there was
less of a need to complete QMDRs as some faults could be identified and actioned
immediately
as
he
had control of the Birmingham engineering budget.
d. Product Samples from Birmingham
British Airways produced ten copies of Product Samples carried
out
at
Birmingham, seven of these related to the period before the accident and were
carried out during work packages involving; Acceptable Deferred Defect
Clearance, Base Checks and Modifications, and Ramp Checks. The seven pre-
accident product samples raised a total of
65
deficiencies which were
of
a minor
nature.
The CAA produced six copies of Product Samples carried out at Birmingham
before the accident; three of these duplicated copies provided by British Airways,
and the additional three, from early
1989,
were similar in content
to
the others.
e. British Airways Quality Audit at Birmingham
Paperwork audits
of
the Engineering function at Birmingham
to
assess the use of
and adherence to monitoring procedures, required under QMP procedures, were
scheduled and performed at six monthly intervals. A physical audit
of
the
Birmingham station,
in
the form of a two day visit, was last carried out prior to
the accident by a representative
of
the British Airways Quality Audit Unit on
15/16
June
1988,
when it was reported that the engineering facility was
to
a high
standard. Seven observations were raised relating
to
minor, non-aircraft, matters.
f.
CAA
Supervisory Visit to British Airways Engineering at Birmingham
One
of
the duties of the
CAA's
Flight Operations Inspectorate
(FOI
7)
was (at the
time of the accident)
to
carry out supervisory visits
to
survey the engineering
services provided by British Airways at Birmingham
in
support of their Air
Operator's Certificate. The last
FOI
7
visit, an 'Air Operator's Certificate:
Supervision of Operator's Line Maintenance Station', before the accident took
place on
22
June
1989
,
followed a proforma schedule, lasted for approximately
half a day and did
not
detect any significant engineering problems.
1.17.3.7
1
.I
7.4
1.17.4.1
Use of
E
1022
hedure at Birmingham
Over the same
39
month period in which
36
QMDRs
were raised,
365 E1022s
were raised at Birmingham.
Fitting
the
windscreen
History of the shift
The Shift Maintenance Manager arrived at work in the offices under the
International Pier
45
minutes earlier than his shift start time in order to allow
himself time to catch up with the paperwork and establish the shift work content;
this included three significant defects, routine items and various minor cabin
defects.
A Supervisory Aircraft Engineer and a further Licenced Aircraft Engineer,
normally part of the shift, were not available that night and, although the work
outstanding remained the same, the Friday night shift was routinely not supported
by the four man night shift supplement because there was reduced scheduled
flying
on
Saturday and Sunday. The shift consisted
of:-
The Shift Maintenance Manager
1
Licenced Aircraft Engineer
1
unlicenced engineer &ame/engines
1
Supervisory Aircraft Engineer (Avionics)
1
Avionics engineer.
The engineers were directed to their tasks whilst the Shift Maintenance Manager
carried
on
with the administration and the task of entering the contents of
the
aircraft technical logs into the computer. At about midnight, the Shift
Maintenance Manager spent some time with the Licenced Aircraft Engineer
on
a
steering defect and the completion of this coincided with the arrival of a Tunisair
Boeing
737
which
the
shift had to handle. As none of the engineers had Boeing
737
experience the Shift Maintenance Manager carried out the pre-departure
inspection and the refuelling in conjunction with the Licenced Aircraft Engineer to
give him experience. All this activity took place at
various
locations around the
airfield and was co-ordinated using radio.
The departure of the Tunisair Boeing
737
at around
0145
hrs
coincided with the
meal break, which the Shift Maintenance Manager spent working
on
administration whilst he ate his sandwiches. After the break he directed his two
airframe engineers onto a galley water leak on one of the BAC One-Eleven aircraft
which needed rectifying before the aircraft departed the following morning.
1.17.4.2
Although there was no operational requirement for G-BJRT the next day, the
Shift Maintenance Manager knew that the oncoming morning shift were also
depleted and that an aircraft wash had been booked, using overtime, at
0630
hrs
the following morning. Whilst no external pressure had been put on him, he was
aware that the previous week the wash team had been brought in on a similar
basis and not used. In order to achieve the windscreen change during his shift
and have
the
aircraft ready for the wash team, he decided
to
carry out the
windscreen change himself.
The aircraft was located in the
No
2 bay,
off
the Eastern Apron on the other side
of the airfield, and was parked tail into the hangar with the nose by
the
doors.
In
retrospect the Shift Maintenance Manager could not recall exactly what the
weather was, but thought that
it
was raining; in which case he would have closed
the doors, leaving a few feet between the nose of the aircraft and the doors. The
windscreen change was carried out between approximately
0300
hrs
and
0500
hrs
on
the Saturday morning.
Procedures used
British Airways statistics show that 12
No
1
windscreens, left
or
right, had been
changed
on
their BAC One-Eleven aircraft over the last year, and a similar
number
the
year before. The Shift Maintenance Manager had carried out about
six windscreen changes
on
BAC One-Eleven aircraft whilst employed by British
Airways.
a.
Maintenance Manual
The Shift Maintenance Manager glanced briefly at the Maintenance Manual as he
had not changed a windscreen for about two years and wanted to refresh his
memory. This check confirmed his impression that
it
was a straightforward job
with no apparent difficulties.
b. LPC
The IPC was available
on
a microfiche reader, but was not used to identify the
part number of the bolts
to
be replaced, consequently a stock check, using
TIME,
to assess the availability and location of replacement bolts was not carried out.
The Shift Maintenance Manager justified this omission by saying that
he
was
quite satisfied that the bolts that he had removed were the correct bolts, and that it
would take
so
much time
to
find
the correct numbers in the IPC that he
did
not
feel justified in
using
the
WJ
in the circumstances of the job
in
question.
The page of the
Ipc
for the
528
series aircraft shows a sketch of
the
pilot's
No
1
windscreen and the adjacent
DV
window, but only illustrates one bolt
-
that in the
DV
window, which is an
A211-7D.
The components for
the
pilot's
No
1
window are listed in the text, along with several alternative modification states,
and its bolts are defined as 'attaching parts' and
are
identified as
A21 1-8Ds.
The
IPC
for the
510
series, in contrast, is very clear in identifying the correct bolts.
The bolts actually
fitted
to
the defective windscreen were, in the main,
A21
1-7Ds,
the bolts illustrated as applicable
to
the
DV
window. That is bolts of the correct
diameter but
0.1
of
an inch shorter than those specified.
c. Bolt selection
The Shift Maintenance Manager removed the windscreen with
the
aid of the
Avionics Supervisor, who also disconnected the electrical connectors of the
screen heaters. The bolts were 'on condition' items, and as some of the paint-
filled bolt heads had been damaged during removal, and others showed signs of
corrosion, the Shift Maintenance Manager decided to replace them and took one
of the bolts to the store to identify
it
by comparison with those held
in
the
carousel. The carousels were under the control of a storeman and had drawers
which were clearly labelled with a location
code
to
which engineers were directed,
after entering the part number into the adjacent stores computer terminal.
Because of their small head size the bolts do not carry individual identification,
but the Shift Maintenance Manager accurately matched the removed bolt by going
through several trays, and comparing the removed bolt with the drawer contents.
He then identified the part number of the bolt as
A21 1-7D
by looking at the stores
issue note
in
the drawer (the windscreen should have been fitted using
A211-
8Ds).
The Stores Supervisor, who had been
in
the job for about
16
years,
informed him that
A21 1-8Ds
were used to fit that windscreen, but did not press
the point. The Shift Maintenance Manager decided that as
A21 1-7D
bolts had
come
out,
he would replace them with bolts
of
the same size.
The minimum stock level
in
the carousel
for
A211-7D
bolts was
50,
but there
were
only
four
or
five bolts
in
the drawer (when checked by the
AAIB
the
following Monday
it
contained four). The Shift Maintenance Manager drove to
the unsupervised carousel underneath the International Pier, taking the removed
bolt with him. The drawers in
this
carousel were labelled with the part number of
the contents, although the labels were old and faded. The ambient illumination
in
this area was poor and
the
Shift Maintenance Manager had
to
interpose himself
between the carousel and
the
light source
to
gain access
to
the relevant carousel
drawers.
He
did not use the drawer labels, even though he now knew the part
number of
the
removed bolt, but identified what he thought were identical bolts
by placing the bolts together and comparing them. He also picked up six A21
1-
9Ds,
thinking that the attachment
of
the outboard corner post fairing strip would
need longer bolts.
The old seal was found
to
be serviceable,
so
the new windscreen, which weighed
60
pounds, was manoeuvred into position and the electrical connections made.
d.
Torque loading
of
the bolts
The aircraft manual calls for a torque of
15
lbf
in
to be applied
to
the bolts, which
are then retorqued
to
5
lbf in after
100
flying hours. The Shift Maintenance
Manager's experience told him that many of the bolts would be found up to three
turns
loose during the retorque procedure,
so
he decided
to
increase the initial
torque
to
20 lbf in.
The British Airways toolstore at Birmingham held a calibrated dial indicating
torque wrench to cover the range of
5
to 120 lbf in, but the retorque requirement
of
5
lbf
in
was at the bottom of the range and the dial indicating torque wrench
was not considered suitable for this task. Two calibrated torque checking gauges
were available at Birmingham to allow engineers
to
confii the wrench accuracy.
The calibrated dial-indicating torque wrench was
not
available on the toolboard
that night, but the Stores Supervisor had recently acquired from British Airways
at London, on
his
own initiative, a torque limiting screwdriver specifically for the
windscreen task, but on receipt
it
was found to be out of calibration date and
it
was therefore not cleared for use.
It
was not the company policy at Birmingham
to
allow the engineers to adjust torque wrenches as and when required, but rather
to
have the wrenches adjusted
in
a standards room and then issued for use at that
specific setting. It was therefore the intention
of
the Stores Supervisor
to
have it
set in
the
London standards room before issue, but, in
the
absence
of
any suitable
alternative, the storeman set this screwdriver
to
the figure
of
20 lbf
in
requested
and gave it to the Shift Maintenance Manager, who checked
the
setting
using
both
torque checking gauges.
The Shift Maintenance Manager used a
3/4
inch bi-hexagonal socket to hold the
No
2 Phillips screwdriver bit onto the speedbrace used
to
run
the
screws down
into the countersinks. The socket did not have any means, such as a spring clip,
to
retain the screwdriver bit, consequently the Shift Maintenance Manager found
that during the two-handed operation
of
using the speedbrace the bit fell out
several times and he had to descend from the safety raiser (mobile staging) and
retrieve it from the floor. To overcome this problem when using
the
same
'/4
inch
bi-hexagonal socket with the torque limiting screwdriver, he held the screwdriver
in his right hand and used his left hand to hold the bit
in
the socket. Additionally,
to
reach most of the
bolts
with both hands from the safety raiser, he had
to
stretch
across
the
nose of the aircraft, outside the safety rail provided by the safety raiser.
This situation was exacerbated by the fact that the safety raiser was incorrectly
positioned alongside the aircraft. His left hand obscured his view of the bolt
head, and the need to stretch removed the operation from his direct vision.
He
fitted
the windscreen using
84
of
the bolts collected from the International
Pier
carousel and obtained a similar feel from the torque limiting screwdriver for each
one; a feel that met his expectations. When he came
to
the outboard corner post
fairing stip he realised that the
A21 1-9D
bolts were too long, descended from the
staging and retieved and refitted the six
old
bolts that he had removed with the
fairing.
The new bolts that
he
had fitted were in fact
A211-8C
bolts
-
one size down in
diameter but with the same thread pitch as those specified and within
0.050
of an
inch in length
to
the
A21 1-7D
bolts removed from the window. The bolts engage
in
10
UNF
'Kaylock' floating anchor nuts; the self locking action is the result of
part of the nut being
an
elliptical shape prior
to
the insertion of the bolt. Some of
the anchor nuts were attached directly to the inside of the aircraft window frame
and some were carried on strips, themselves attached
to
the window frame. The
outboard corner post fairing strip interposed an additional thickness and
required
A211-8D
bolts, and these were specified for the attachment of the whole
windscreen, even though in the majority of locations approximately five threads
would be visible below an anchor nut fastened directly
to
the frame when used
with
an
A21 1-8D
bolt. The amount
of
thread
in safety would be reduced when
used with the backing strips and the outboard corner post fairing.
e. Missedcues
The safety raiser used by the Shift Maintenance Manager did not give easy access
across to the centreline
of
the aircraft, and he had
to
stretch over the aircraft nose
to
accomplish the task.
Due
to
the
inadequate access
to
the job and the obscuring
effect of his left hand the Shift Maintenance Manager was not in a position
to
observe that the bolt thread was slipping in the anchor nut thread, instead of the
torque limiting screwdriver allowing its shaft to remain stationary while the
handle rotated. However, the bit and socket would have continued to rotate
in
his
left hand.
The window was finished in primer and had countersunk holes for the bolts; an
A211-8C
bolt head sits significantly further below the surface of the window,
down in the countersink, than does an
A211-8D
bolt head, leaving an annulus of
unfilled countersink which is easily discernable when viewed under good
conditions. This excessive annulus of unfilled countersink was not seen.
When the bolts were being fitted
to
the windscreen centre column, the bolts from
the right hand window, the heads
of
which filled the countersinks, were close to
those
of
the left hand window, and, although painted, the difference is perceptible
under normal circumstances. The Shift Maintenance Manager missed this
difference in depth of the bolt heads in the windscreen centre column. (See
photograph
in
Appendix
E).
When fitting the outside corner post fairing with the six bolts previously removed
from
it,
the Shift Maintenance Manager failed to notice the difference
in
torque
achieved or the difference in countersink
fit
of
the bolt heads between the old and
new bolts.
The following night the Shift Maintenance Manager carried out another
windscreen change, this time a right hand one. The job had been set
up
before he
arrived and he noticed that the bolts were A21 1-8Ds. He recalled fitting A21 1-7D
bolts the previous night, but
he
rationalised that the aircraft were old and of
differing modification states and the previous night
he
had
an
aircraft modification
standard requiring A211-7D bolts and that night he had an aircraft requiring
A21
1-8D bolts.
f. Documentation
The documentation used
to
report and clear the defect stated:-
DEFECT SYMPTOM ACTION
TAKEN
SYSTEM
Port Windscreen
During cruise darkening
&
bubbling
noted
in
small area on bottom LH
port
windscreen. Q.R.H. drill carried out.
Windscreen replaced.
A.S.R. Actioned.
F/Check satis
SIGNED BY REPORTING CAPTAIN SIGNED BY ENGINEER
(SUBJECT TO
THE
FOLLOWING DECLARATION)
THE
WORK RECORDED
ABOVE
HAS BEEN CARRIED
OUT
IN
ACCORDANCE WITH
THE REQUIREMENTS OF THE AIR NAVIGATION ORDER FOR
THE
TIME BEING
IN
FORCE
AND
IN THAT RESPECT THE AIRCRAFI"/EQUIPMENT IS CONSIDERED FIT
FOR RELEASE TO SERVICE
Note:
Q.R.H Quick Reference Handbook.
A.S.R
F/Check
Air
Safety Report, raised by the captain. The Shift Maintenance
Manager's action was to clear the defect.
Functional check
of
the windscreen heating system.
1
.I
7.5
Prevalent
attituaks
During the course of the investigation a number of visits to the operator's
engineering facility at Birmingham were made, the Shift Maintenance Manager
who changed the windscreen was interviewed and informal interviews conducted
with the other maintenance managers in order to provide a context for the actions
of the engineer who undertook the windscreen replacement task. Subsequently
these managers provided written signed statements, mostly concerned with the
range of issues raised at the interviews.
The overriding impression given by the Maintenance Managers was that morale
was high and that they were proud
of
their
record
in meeting the task and of the
way that they went about
it.
The Shift Maintenance Managers
did
not criticise the shift system, however the
potential problems associated with sleep deprivation and circadian effects were
acknowledged and various strategies were cited
to
cope with the situation.
During the initial part
of
the investigation the Shift Maintenance Manager who
carried out the windscreen
fit
did not appear
to
grasp the lack of care that his
actions implied. He co-operated fully in the investigation and, when shown the
full list of errors and omissions that he had made, offered an explanation for each
individual action.
The Area Manager was aware of the pressures to produce aircraft that the Shift
Maintenance Managers worked under, and continually stressed that there were
other objectives besides maximising the work throughput on the shifts.
Four of the
six
Maintenance Managers who subsequently gave written statements
raised the issue of the large numbers of E1022 forms originated at Birmingham
and concluded that these indicated their concern for quality and general standards.
One Maintenance Manager stated that he felt that the
QMP
system was
in
its
infancy at the time of the accident but that the E1022 process was well known.
He went on to say that the staff at Birmingham felt more comfortable with the
E1022 system because they knew exactly how it worked and they knew that they
would get a response.
Another Maintenance Manager also concluded that when he returned damaged
parts through the E1022 system he had direct contact with the development
engineerr by telephone and his requests were actioned without them being
channelled through a third party. The E1022 system was therefore more
effective, the
QMPs
took longer
to
action and were,
in
his opinion, clearly for
non-urgent
quality
lapses.
I .I
7.6
Human
factors
1.17.6.1 Personal details
The person who fitted the windscreen was a Shift Maintenance Manager holding
authorisations on BAC One-Eleven, Boeing 737, Boeing 757, HS 748 and with
transit authorisations on L-1011 Tristar,
Boeing
747 and a CAA licence holder for
airframe and engines on the Viscount.
His
experience included
10
years
in
the
RAF,
followed by 23 years with British Airways. He appeared
to
be a mature,
dedicated engineer who was well respected by flightcrew and engineers alike.
No
domestic or financial distractions were identified, either by British Airways
management, the Behavoural Psychologist engaged by the AAIB who
interviewed him or the AAIB Inspectors; the Shift Maintenance Manager denied
any such problems.
He had been on leave over the
period
of the last night shift carried
out
by his shift
and
so
the
Friday/Saturday night shift during which
the
windscreen was fitted
was his first night work for approximately five weeks. He had had a normal
nights sleep the previous night and had gone to bed at about
1730
hrs,
and had
slept for
11/2
hours, getting up at 2030
hrs.
He said that
he
would have been
happier if he had slept for
an
hour longer, but wasn't dismayed that he had not.
The last shift worked by the Shift Maintenance Manager was
on
Tuesday
5
June
from 0630 hrs
to
1500
hrs.
The Shift Maintenance Manager made
limited
use of a fairly weak prescription for
reading glasses, but did not habitually use them at work and was not wearing
them when making the bolt selection.
His
record with British Airways has been reported as exemplary and
he
had
received commendations during this period.
1.17.6.2 Behavoural Psychologists's Report
A Behavoural Psychologist interviewed the Shift Maintenance Manager who
carried
out
the windscreen fitting task and was present during AAIB interviews
with him and informal interviews with the other Maintenance Managers. His
report is included at Appendix
F.
1.17.6.3
Opthalmologist's Report
The Shift Maintenance Manager was examined by a consultant in opthalmology
who concluded that his eyes were normal with full central fields and normal
ocular muscle balance. He had full stereoscopic vision and his intra-ocular
pressures were normal. However he was presbyopic and for this he needed
glasses for close work, and his own half-eye reading glasses were perfectly
adequate for his needs.
If
he were
to
read small print
or
figures without his reading glasses, he would
have difficulty. With his reading glasses and in
good
lighting, he would have
no
problems.
1.17.6.4
Relationship between Serious Accidents and Near Misses
Two analyses
of
groups
of
accidents and incidents occurring in industrial
situations have shown that for every serious accident there can
be
between
4001
to
6002
near misses. These figures indicate that, in an industrial context, degraded
standards may exist for some time before a serious accident occurs
or
the situation
becomes apparent
to
an
independent observer.
The experience of accidents involving aircraft maintenance shows that
an
accident
usually occurs as a result of a series of errors, and that the probability of the
accident occurring is low compared with the probabilities of the individual failures
in
the chain
of
events leading
to
it.
The incorrect installation
of
the windscreen
resulted from a sequence of contributory events
(
para
1.17.4.2),
any one of
which,
if
identified and eliminated from the chain could have prevented the
windscreen loss.
I
.I
7.7
The
efsects
of
rapid decompression
In
an attempt to analyse and quantify the dynamic forces and physiological effects
caused by the loss of
the
windscreen, all the available data was presented to the
Aircrew Systems Division of the
RAF
Institute
of
Aviation Medicine,
RAE
Farnborough.
The conclusions drawn suggested that the critical factors affecting the
survivability
of
all the aircraft occupants were the time of decompression and the
final cabin altitude. Those affecting the commander were the time of
Per TyePearson
Per
Frank
Bird
1.18
decompression and the final altitude
of
exposure, together with the low
temperature and the aerodynamic forces to which
he
was exposed during
the
remainder
of
the flight.
Calculation provided that the duration of the decompression was likely to have
been in the region of
1.13
to
1.46
seconds, and this was supported by the
duration of
the
rapid changes
of
aircraft attitude. The maximum cabin altitude,
achieved during this time period, depended upon the interaction between the
ram
effect
of
the outside airflow and the airflow provided by the internal
pressurisation systems. Analysis suggested that this was unlikely to have been
greater than 13,000
to
13,500 feet which, when followed by the descent profile
flown, would not have promoted sufficient hypoxia
to
impair either the
passengers or the crew.
The forces acting upon the commander, to project him through the windscreen
aperture, were a function of the differential pressure between the inside and
outside of the cabin and
are
calculated
as
having a force
of
approximately
5,357
pounds (depending upon
his
exact proximity
to
the aperture). This would be
quite adequate
to
drive
a
person weighing
70
kg from his seat and through the
aperture, whereafter the ram effect
of
the airstream would pin him to the fuselage
and seriously impair movement.
New investigation techniques
None.
2
2.1
Analysis
General
The crew were faced with an instantaneous and unforeseen emergency.
The
combined actions of the co-pilot and cabin crew successfully averted what could
have been a major catastrophe. The fact that all those on board the aircraft
survived is a tribute
to
their quick thinking and perseverance in the face of a
shocking experience.
Up to the time of the loss of the windscreen, the flight had proceeded
uneventfully and in accordance with the company's normal procedures.
It
was
quite
in
order for the flight crew to release their shoulder harnesses once they
were established in the climb and, for reasons
of
comfort, the commander
loosened his lap strap as he neared the cruising phase of the two and a half hour
flight
to
Malaga. Therefore, when the left windscreen was blown out, it was not
surprising that the commander, who was very lightly built, was drawn partially
through the windscreen aperture. It is not certain what prevented his complete
egress from the aircraft but, since the
No
2
steward later had to free his legs from
a position between the control column and the flight deck coaming, it is likely that
he had been restrained by his legs during the initial stage of the emergency.
Later, he was restrained simply by the efforts of the
No
2
steward who was
holding
on
to both of his legs.
The co-pilot immediately took control of the aircraft and was able
to
establish a
rapid descent despite the disorientating effects of the dramatically transformed
cockpit environment coupled with a push over and right roll.
It
was fortunate that
he was
an
experienced pilot with more than
1,OOO
hours experience of flying the
BAC
One-Eleven aircraft.
Thus
he was able to handle the aircraft on his own and
complete the normal operating procedures from memory without the assistance of
another pilot. He alone was faced with a double emergency, namely rapid
decompression and incapacitation of the handling pilot. He rejected the idea of
donning his oxygen mask in favour
of
being able to shout instructions
to
his
cabin crew.
In
the event, this was probably sensible but if the depressurisation
had occurred at a greater height, say above
20,000
feet,
it
would have been
imperative for him to don the oxygen mask to avoid incapacitation
to
the extent
that he could not fly the aircraft.
2.2
Engineering
Factors
2.2.1
The
selection
and
use
of
the wrong bolts
The windscreen was lost because
it
had been secured by bolts, the vast majority
of
which were of an incorrect diameter. The windscreen fitting process was
characterised by
a
series
of
poor work practices, poor judgements and perceptual
errors, each one
of
which eroded
the
factors
of
safety built into the method of
operation promulgated by British Airways:-
a. During the fitment of the windscreen to G-BJRT the Shift Maintenance
Manager was confronted with certain situations which made his job more
difficult:-
Incorrect bolts, A21 1-7D
had
been used
in
the previous installation
Insufficient stock
of
A21 1-7D bolts, incorrect but demonstrably adequate,
existed
in
the carousel in the bay stores at the Eastern Apron.
Nevertheless, problems
of
this type are not unusual and cannot
be
used to explain
the subsequent chain of events which led to the loss of the windscreen.
b. A number of procedures were ignored and some poor trade practices
followed:
-
The
IPC,
available to identify the
required
bolts' part number was not used
The stores
TIME
system, available
to
identify the stock level and location of
the
required bolts, was not used
Physical matching of old and new bolts by touch and eye was attempted,
leading to a mismatch with bolts from the International pier carousel
Arbitrary choice
of
A21 1-9Ds to
fit
through
the comer fairing took place
An increase
in
bolt torque over that stated in the Maintenance Manual was
used.
c. Non conformity with British Airways standards was also demonstrated:-
An uncontrolled torque limiting screwdriver was set up outside
the
Calibration Room.
d. Use of unsuitable equipment took place:-
2.2.2
A
bi-hexagonal bit holder was used leading
to
occasional loss of the bit and
covering of the bolt head during the torquing process
A
Safety Raiser which provided inadequate access to the job was used.
e.
A
number of cues were either ignored
or
missed:-
The warning from the Storekeeper that
A2
1 1
-8D
bolts were required did not
influence the choice of bolts
The amount of unfilled countersink left by the small boltheads was not
recognised as excessive
The increased amount of unfilled countersink with
the
new bolts, compared
to the flush fitting of adjacent, correctly sized bolt heads in the windscreen
centre column, went unnoticed
The difference in torque and the amount of countersink remaining unfilled
between the new bolts and old bolts used
in
the corner fairing went
unnoticed
The use of, as he thought,
A21 1-7Ds
when using
A21 1-8Ds
the
next night
was not questioned
The difference between the bolt thread stripping idthrough the nut and the
torque limiting screwdriver 'breaking' was not recognised even though the
bi-hexagonal socket and screwdriver bit, located by his left hand, were still
rotating. However, the high residual torque of the particular screwdriver
resulted in a less positive 'break' and, although the break torque was never
achieved with the
8
UNC bolts,
it
was when setting the screwdriver and
when installing the fairing. This screwdriver, on reaching the set torque
may have felt more like the thread stripping than would one with a more
'snappy' break.
The
windscreen replacement task
The windscreen is part of the aircraft's pressurised hull and is attached from the
outside by
90
bolts. It may be the only critical item
on
the aircraft that was
susceptible
to
failure
through
the chain of circumstances listed above, in that:-
a. Its replacement required the renewal of the majority of the bolts in the
judgement
of
the Shift Maintenance Manager.
b. The wrong diameter bolts engaged with the anchor nuts, and had
the
same
thread
pitch.
c. The bolts were not special
to
type items needing a part number
to
identify and obtain replacements, but were general use items, obtainable
from an uncontrolled carousel.
d. The windscreen was not designed on
the
plug principle such that
internal
air
pressure would hold
it
in place, but was fitted from the outside.
e.
The windscreen replacement was not designated a 'Vital Point' task,
therefore no duplicate inspection was required.
f. The Shift Maintenance Manager was the only person whose work on the
night shift was
not
subject to
the
review of a maintenance manager.
The windscreen may therefore have been unique
in
that
it
alone, of
all
the critical
components, could have accommodated the errors which occurred during its
fitment,
to
expose them
so
dramatically the first time that the windscreen was
called upon
to
resist cabin pressure. Had
it
been any other item, the selection of
the wrong bolts may have been unmistakably apparent during the fitting process,
or the subsequent failure may not have been
so
obvious
or
traumatic.
2.2.3
Relevant British Airways' Procedures
2.2.3.1
AGS
dispensing
The use of unsupervised dispensers for aircraft general spares is a recognised and
necessary part of aircraft engineering practice. Small units can rarely afford to
keep a full-time storekeeper to administer a dispenser,
or
even a store, and
good
trade practice has to
be
relied upon. Before the Shift Maintenance Manager went
to the unmanned carousel he knew the part number
of
the bolts
he
was seeking,
and although they were too short, similar bolts had held the old windscreen in
place for four years. Despite the poor segregation, labelling and lighting, the
selection
of
the wrong bolts cannot be explained by the carousel system.
2.2.3.2
Work by Shift Maintenance Managers
During the course of his duties the Shift Maintenance Manager reviewed the work
of
his shift, this review augmented the self certification task required of the
engineers by British Airways' maintenance policy. Once he had decided to cany
out rectification work himself,
he
withdrew from the active supervision
of
the rest
of
the shift. The task of the windscreen installation was not designated a
2.2.4
2.2.4.1
2.2.4.2
'Vital Point' and consequently no duplicate inspection was called
for
and none
took place, nor was the work
of
the Shift Maintenance Manager subject
to
review
by another manager.
Thus
the Shift Maintenance Manager had no backstop with any chance
of
detecting his
errors.
Errors that were made more likely by the sleep deprivation
and circadian effects associated with the end
of
a first night shift.
Quality
Assurance
Application of Self Certification
to
Aircraft Engineering
The adoption
of
self certification systems within manufacturing industry has
typically resulted
in
savings, mainly arising through reduction
in
scrap and in the
achievement of higher manufacturing efficiency. Nevertheless, at the end
of
the
production line the product is normally still tested, before being despatched.
Some aircraft maintenance tasks which may
be
undertaken
using
self certification
procedures do not allow for the testing
of
the end product before
it
is
flown.
It could
be
argued that the concept of self certification suffers from the drawback
that
the
expectations of the engineer are such that he is unlikely
to
detect
an
error
of his own making; the application of self certification reduces the level
of
inspection and supervision.
It is recommended that the applicability of self certification
to
aircraft engineering
safety critical tasks following which the components
or
systems
are
cleared for
service without functional checks, should
be
reviewed by the CAA. Such a
review should include
the
interpretation of 'single mal-assembly' within the
context of 'Vital Points' and the requirements which include a waiver making the
definition
of
'Vital Points' non-mandatory for aircraft with a Maximum Take-Off
Weight Authorised of over
5,700
kg which were manufactured
in
accordance
with a Type Certificate issued prior to
1
January
1986.
Feedback
A fundamental requirement
of
any management process is a feedback loop to
detect the success or failure of the system, and
two
types of feedback
are
available
-
a formal feedback through auditing/monitoring activities and an informal
feedback through free discussion amongst engineers discussing their work
problems in an open forum.
Some feedback was generated by the monitoring of a series of performance
parameters which were airline parameters with quality overtones rather than
parameters capable of giving a comprehensive picture of the engineering quality
built into tasks. The crucial element missing was direct assessment
of
the
standards used by the Shift Maintenance Managers to perform their tasks.
Whilst literature circulated by British Airways stressed the need for open
reporting through QMDRs, a number of the Maintenance Managers indicated that
they felt more comfortable with the E1022, Ground Occurrence Report
Form,
with which they were particularly familiar, finding
it
a more
direct
and responsive
reporting system. The findings at Birmingham are consistent with the British
Airways Audit Team sampling of QMP awareness in 1988 and a further QMP
survey
in
1989 which identified that a lack of comprehension still existed. At the
time of the accident action to remedy this was
still
under discussion within British
Airways.
The E1022 system was well established and understood when QMP was
introduced three years before the accident. The statements
of
the Birmingham
Maintenance Managers indicate that at least some of them still prefer, and may
use, the E1022 system in instances when a QMDR might be more appropriate.
The list
of
circumstances under which
an
E1022 is to be used appears
to
overlap
into
procedural areas which might be thought of as the domain of the QMP
system.
Some evidence
of
a quality problem within the British Airways engineering
unit
at
Birmingham is provided by the failure
of
the unit to use the Continuous
Monitoring system to report some of the problems seen during investigation of
the windscreen fitment:-
The poor labelling and segregation
of
parts
in
the uncontrolled carousel
under
the
International Pier
Inadequate access available to certain areas
of
the aircraft from the work
platform
Inadequate tools
to
achieve some specific torque loading
Windscreen attachment bolts found loose at the 100 hour re-torque.
It
is recommended that British Airways review their Quality Assurance system
and the relative roles of E1022s
and
QMDRs
be
clarified and that they continue
to
educate and encourage their engineers
to
provide feedback from the shop
floor.
2.2.4.3
Local
Management
The Area Maintenance Manager did not directly observe
the
work methods of the
engineers at Birmingham.
His
involvement in monitoring consisted of processing
the monthly Product Samples and the
QMDRs
raised by his staff, along with
monitoring levels and trends of a set of performance parameters on the BAC One-
Eleven fleet. Whilst these parameters may form part
of
a quality monitoring
system they are inadequate
to
inform management about the standards used by
individual Shift Maintenance Managers.
The Station Maintenance Manager was directly responsible
for
the work
of
the
Shift Maintenance Managers, and he was also responsible for carrying out
Product Samples on his area. Because his job required him
to
work during the
day he was rarely present during the night shift.
No
evidence was presented of
any 'in-place' system
to
monitor the standards used by individual Shift
Maintenance Managers.
The relationship between the Station Maintenance Manager and the Shift
Maintenance Managers was ill-defined, there was no clear delegation of duties,
itemised terms of reference were not available and the duties
of
the Shift
Maintenance Managers were not documented.
As a result of the lack of specific direction of duties neither the Area Maintenance
Manager nor the Station Maintenance Manager observed the standards employed
by individual Shift Maintenance Managers.
It is recommended that British Airways should review the need
to
introduce job
descriptions/terms
of
reference for engineering grades of Shift Maintenance
Manager and above.
2.2.4.4
Product Samples and Quality Audits
The principle that personnel carrying
out
quality audits should be independent of
the specific activities or areas being monitored is reflected in British Airways'
documentation. The same principle
of
independence should apply
to
the Product
Samples, even though they were a check on standards rather than an audit.
However, not only were the Product Samples at Birmingham carried out by the
person who had direct managerial responsibility for the tasks, but the results were
sent to
the
British Airways Quality Audit Unit for the attention of the
CAA.
It
is
unreasonable
to
expect that someone who has condoned, or not recognised, the
practice as a manager will report it under the aegis of his quality assurance
responsibilities
to
such bodies.
At the time of the accident a physical audit of the Birmingham base was about due
according to the QMP schedule. The British Airways Quality Audit Unit had last
visited Birmingham two years before the accident over a
two
day period and were
satisfied with the engineering standards.
It is recommended that British Airways should review the Product Sample
procedure with a view to achieving an independent assessment of standards and
conduct an in-depth audit into the work practices at Birmingham.
2.2.4.5
CAA
Supervisory Visits
The
CAA
supervision of the engineering functions of operators, away from their
main bases, is undertaken by FOI
7,
and the British Airways engineering facility
at Birmingham was given a half-day visit approximately a
year
before the
accident. The visit, in view
of
the time allocated, was necessarily superficial and
only likely
to
have picked up
gross
discrepancies.
It
is recommended that the CAA should review the purpose and scope of the
FOI
7
Supervisory Visit.
2.2.5
Technical
standurds
Every engineer was responsible for the quality of his own work under the British
Airways QMP. Quality standards at Birmingham were the responsibility of the
local management; the Area Manager and his deputy, the Station Maintenance
Manager, as part of their routine daily management task. Additionally
the
monthly Product Samples looked at methods and standards of work. Further
quality monitoring was conducted during audits by the British Airways Quality
Audit Unit and supervisory visits by the CAA.
Thus
any explanation of how
inadequate work standards came to be employed on the night in question would
also
have to explain how the various quality and management monitors failed to
detect earlier evidence
of
such inadequate standards. This could have been
because the Shift Maintenance Manager had generally maintained high standards
and his actions on the night were not representative of his normal standards
or
the
monitoring procedures had failed to detect inadequate standards employed by him
for some time,
or
some combination of the two. The
two
extreme explanations
are categorised as follows:-
a. The Random Failure Theory
The lapses on that night were a 'one-off and therefore there had not been
any previous symptoms to alert managemendquality monitors.
b. The Systems
Failure
Theory
The lapses were typical of standards employed by the Shift Maintenance
Manager, which were either known
to
the managemendquality monitors,
who condoned them,
or
were not known to them because they had been
unable to monitor the situation satisfactorily.
The track record
of
the
One-Eleven fleet at Birmingham, in terms of the
engineering criteria monitored, indicated that standards were generally
good
and
the Product Samples and Continuous Monitoring reported only minor
discrepancies. This impression of a satisfactory operation, gained from in-house
sampling at Birmingham, was supported by independent information from
the
physical audit carried out by British Airways Quality Audit Unit and the visit by
the CAA. However, such quality lapses as those perpetrated by the Shift
Maintenance Manager would not have been apparent
to
other than detailed
observation until combined with such a task as the windscreen change.
(See
Paragraphs 2.2.1 and 2.2.2).
Some studies
on
the effects
of
human error on industrial safety indicate that the
ratio
of
near misses
to
serious accidents could be as high as
600:1,
therefore
inadequate standards can be applied over a considerable period of time before
giving rise
to
a reportable accident
or
notifiable occurrence. This implies that a
series of degraded procedures could be applied over a period
of
time without
becoming apparent.
British Airways point
to
the exemplary record of the Shift Maintenance Manager
throughout his service with them as being proof
of
the continuing satisfaction
of
local management with the Shift Maintenance Manager's standards, and that
record as being incompatible with anything other than an isolated example of
inadequate work standards.
The Behavoural Psychologist described the Shift Maintenance Manager as
conscientious and pragmatic rather than conscientious and meticulous. The
behaviour of a man who, based on experience, changed the mandatory torque
setting for the bolts, visually matched the replacement bolts, and arbitrarily
selected A21 1-9D bolts for the fairing is compatible with that description only if
he believed that these practices were accepted at Birmingham (whether
or
not
they
were in fact accepted).
Many
of
the actions taken that night by the Shift Maintenance Manager may be
described as evidence of a lack of sufficient care in the execution
of
his
responsibilities. Such a catalogue
of
events does not equate to a momentary lapse
in
behaviour but is more indicative
of
the approach of a conscientious and
pragmatic engineer working
in
an non-procedural manner. Such a description of
the individual is not necessarily inconsistent with his 'exemplary record, because
until matched with a task such as this windscreen change, his approach was
capable of going undetected by anything other than a close observation of his
work practices.
At no time was any evidence presented
to
indicate that the standards and practices
used on that night were in any way different from those used generally by the
Shift Maintenance Manager. Nor were any external
or
job-related pressures
identified which may have caused a lack
of
concentration. Indeed, even when
shown the
full
list of errors and omissions that
he
had made, he still offered an
explanation for each individual action.
The number
of
errors perpetrated on the night of this job came about because
procedures were abused, 'short-cuts' employed and mandatory instructions
ignored. Even when doubt existed about the correct size of bolt
to
use, the
authoritative documents were not consulted. After
the
event the Shift
Maintenance Manager concerned demonstrated a lack of appreciation of the
significance of failure to adhere
to
the specified procedures,
good
trade practices
and even the requirements of the Maintenance Manual. This makes
it
most
unlikely, in the view of the
AAIB,
that the practices which permitted such errors
were 'one-offs' but supports the argument for a longer term failure by the Shift
Maintenance Manager
to
observe the promulgated procedures.
Such compromised standards on the part
of
the Shift Maintenance Manager
cannot explain all of the errors which
led
to
the accident, such
as
his failure to
react
to
the various cues indicating that something was wrong. However, they
did reduce his potential to achieve quality in the task and provided a context in
which mistakes could
go
undetected, building into
a
critical chain.
Thus
the explanation
of
how the catalogue of errors occurred on the night in
question lies somewhere on the continuum between the stated extremes
of
Random and System Theories with contributions from each. The system element
being that which accommodated the application
of
inadequate standards by the
Shift Maintenance Manager for some time and the perceptual errors contributing
the random element.
2.2.6
Engineering Requirements
2.2.6.1
Periodic training and testing
There is clear evidence
of
a different philosophy applied
to
pilots, who are
required
to
undergo regular line and base standardisation checks, and engineers
who are not subjected
to
any comparable standardisation
or
refresher checks.
An experienced Licenced Engineer with an exemplemy record demonstrated an
abuse
of
procedures, employed short cuts, ignored mandatory instructions and
failed
to
conform with what is generally regarded as 'good trade practice'.
Therefore,
it
is recommended that the need for periodic training and testing
of
maintenance engineers should be reviewed by the
CAA.
2.2.6.2
Check
lists
and technical documentation
The work of flightcrew during routine and emergency operations is highly
formalised, with check lists
to
be followed
at
critical stages of the flight. Even
though they may have already performed the operation several times previously
that day,
the
flightcrew will still follow a check list, item by item, on each
occasion, and in some cases individual responses will be monitored by another
crew member. Whilst the use
of
the Maintenance Manual is mandatory and some
of the processes detailed
in
it
are
complex, apart from work on flying and engine
controls, and 'Vital Points' (if defined) an authorised engineer may work on
an
aircraft unsupervised and unchecked.
In
spite of the itemised nature of the procedures detailed
in
the Maintenance
Manual, in some areas on work not involving flying and engine controls,
including the
BAC
One-Eleven windscreen change, an engineer may clear the
documentation with a one line statement saying
in
effect, 'Defect cleared', with a
pre-printed Release
to
Service certificate contained on the form. The use of
an
itemised servicing procedure in the form of a document that requires signatures at
each stage is considered to be a valuable aid to ensuring that the correct process
has been acknowledged and signed for.
2.2.6.3
Eyesight standards
The Shift Maintenance Manager required mild corrective lenses
to
read small print
or
figures and he did not use his glasses whilst performing the windscreen
replacement. The lack
of
corrective glasses cannot account
for
the majority
of
the
errors made that night, but may have subconsciously influenced the Shift
Maintenance Manager in short circuiting some
of
the procedures which rely on
adequate eyesight.
It
is recommended that the CAA should recognise the need for the use of
corrective glasses,
if
prescribed, in association with the undertaking of aircraft
engineering tasks.
2.3
ATC
Emergency procedures
In
the circumstances it was imperative that the co-pilot was given
all
the help that
could be made available. In this case the Bristol Sector Controller neither
complied with the co-pilot's specific request for radar navigational assistance, nor
did he advise the flight
of
its position
or
give any relevant information regarding
Southampton, such as current weather, runway in use, pressure settings, etc, as
would have been expected
Given that emergencies are rare,
it
is inadvisable to leave to chance the possibility
of
a controller having experience in such a situation. The provision
of
training
in
the handling of emergencies and other infrequent occurrences is therefore
considered
to
be essential. A persuasive argument in favour of emergency
training is that adequate preparation can lessen the stress which may be induced in
the real situation. While such an argument has a
good
deal of face validity,
supporting data
are
not easy to find. Nevertheless, experiencing similar situations
in training and learning
to
cope, should instil in the individual a degree of
confidence in his ability
to
handle real events. Emergency evacuation and fire
drills
are
conducted on this premise.
It is sometimes argued that training for emergencies is not possible because
all
emergencies
are
essentially different from each other, cannot be anticipated and
therefore cannot be programmed into a course of training. The fact that
emergencies will differ in detail or in the precise accumulation of events which
lead to their occurrence, does not, however, negate the value of training. All too
often emergency training focuses on the use
of
a limited number
of
problem
situations. These become familiar
to
trainees and are seldom updated from one
training course
to
the next. Not only will trainees lack the ability to cope with
other events, but this method encourages a tendency to fit novel situations
into
known patterns using strategies which have worked in the past but may not be
applicable to the current problems. During training a variety of scenarios should
be employed
to
provide both experience in coping with a number
of
different
situations and the opportunity to build confidence in handling them.
Whilst no two emergencies may be identical, there are a number of basic steps
which have to be taken
in
dealing with them.
In
ATC terms this would include
ensuring that there are no other conflicting aircraft, ascertaining the extent of
the
problem, informing the appropriate emergency services, etc.
If
these predictable
elements
of
emergency handling are well trained and automatic they release 'spare
capacity' which can
be
devoted
to
coping with the unanticipated or unique aspects
of each case.
The Bristol Sector Controller quite properly intended
to
allow his actions to be
guided by the decisions
of
the co-pilot and the Bristol CSC but he formulated no
specific plan of action to deal with the emergency.
No
training programme,
however well constructed, can guarantee the trainee's performance during a
genuine emergency. However, more preparation for handling emergencies
during both initial training and
as
part of a systematic pattern of refresher training
and skill maintenance may help controllers involved
in
incidents
to
realise that
such events can happen and would prepare them
to
accept the reality of the
situation and
to
cope with
it
more effectively.
It is recommended that the Authority ensure that prior
to
the issue
of
an ATC
rating a candidate shall undergo an approved course which includes training in
both
the theoretical and practical handling of emergency situations. This training
should then be enhanced at the validation stage and later by regular continuation
and refresher exercises.
Conclusions
Findings
The crew were properly licenced, medically
fit
and rested
to
conduct the
flight.
The take-off and initial climb from Birmingham were uneventful.
Whilst climbing through 17,300 feet pressure altitude and on a heading
of 195'M,
the
left windscreen was blown out of its frame under the
influence
of
cabin air pressure.
The commander was sucked partially out
of
the windscreen aperture and
blown backwards over the flight deck roof. He was restrained from
further egress by the cabin staff who held onto him until after the aircraft
had landed.
The co-pilot suffered a degree of disorientation but he was able to regain
control
of
the aircraft and
start
an immediate descent.
The remaining crew and passengers suffered
no
ill
effects from the rapid
decompression and lack of oxygen.
It
has been calculated that the cabin
altitude was unlikely
to
have been greater than 13,000 to 13,500 feet,
achieved within
two
seconds after the loss of cabin pressure.
The left windscreen had been replaced and the task certificated by the
same Shift Maintenance Manager with the appropriate British Airways
authorisation 27 hours before the accident flight and the aircraft had not
flown since its replacement.
The replacement windscreen had been installed
with
84
bolts (A211-8C)
whose diameters were approximately 0.026
of
an inch below the
diameters
of
the specified bolts (A211-8D), and
6
bolts (A211-7D)
which were of the correct diameter, but
0.1
of
an inch too short.
The windscreen fitting process was characterised by a series
of
poor
work practices, poor judgements and perceptual errors, each one of
which eroded the factors
of
safety built into the method of operation
promulgated by British Airways.
(xii)
(xiii)
(xiv)
(mi)
(xvii)
(xviii)
A series of cues were available
to
the Shift Maintenance Manager
to
draw attention to the use of incorrect bolts but all went unnoticed
or
unheeded.
Although an independent final inspection would have had a high
probability of detecting the error, the task of the windscreen installation
was not designated a 'Vital
Point'
and consequently no duplicate
inspection was called for and none took place.
The work
of
the Shift Maintenance Manager was
not
subject
to
review
by another manager and thus the there was no backstop with any chance
of detecting his errors. Errors that were made more likely by the sleep
deprivation and circadian effects associated with the end of a fist night
shift.
The practices employed by the Shift Maintenance Manager which
permitted such errors were not considered
to
be 'one-offs' but were
symptomatic of a longer term failure on his part to observe the
promulgated procedures.
The British Airways
local
management, Product Samples and Quality
Audits had not detected the application of inadequate standards by the
Shift Maintenance Manager, because they did
not
monitor directly the
working practices
of
Shift Maintenance Managers.
The windscreen replacement task may have been unique in that
it
alone
could accommodate the errors associated with its fitment, such that they
were exposed
so
dramatically the first time that the windscreen was
called upon
to
resist cabin pressure.
The
CAA
supervisory visit was superficial and as such did not monitor
the working practices of Shift Maintenance Managers.
The British Airways local Product Samples at Birmingham did not
provide an independent assessment
of
standards as they were carried out
by the person who had direct managerial responsibility for the tasks.
Literature circulated by British Airways stressed the need for open
reporting through QMDRs, however, a number of the Maintenance
Managers indicated that they felt more comfortable with the E1022,
Ground Occurrence Report
Form,
with which they were particularly
familiar, finding it a more direct and responsive reporting system.
(xix)
The Shift Maintenance Manager required mild corrective lenses
to
read
small print
or
figures but did not use his glasses whilst performing the
windscreen replacement.
(xx)
Following receipt
of
the co-pilot's distress message, and when two way
communication had been re-established, ATC facilitated diversion of the
flight to Southampton Airport.
(xxi)
The nature of the emergency was never fully appreciated by LATCC.
(xxii)
The Bristol Sector Controller's training in the handling of emergency
situations was probably inadequate.
(xxiii)
The recovery to Southampton was managed effectively by the co-pilot
who was assisted by the Southampton Zone Controller.
Causal
factors:-
0)
A safety critical task, not identified as a 'Vital Point', was undertaken by
one individual who also carried total responsibility for
the
quality
achieved and the installation was not tested until the aircraft was
airborne on a passenger carrying flight.
(ii)
The Shift Maintenance Manager's potential to achieve quality
in
the
windscreen fitting process was eroded by his inadequate care, poor
trade practices, failure
to
adhere to company standards and use of
unsuitable equipment, which were judged symptomatic of a longer term
failure by him to observe the promulgated procedures.
(iii)
The British Airways local management, Product Samples and Quality
Audits had not detected the existence of inadequate standards employed
by the Shift Maintenance Manager because they did not monitor directly
the working practices
of
Shift Maintenance Managers.
4
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
Safety Recommendations
The CAA should examine the applicability of self certification to aircraft
engineering safety critical tasks following which the components
or
systems are
cleared for service without functional checks. Such
a
review should include the
interpretation of 'single mal-assembly' within the context of 'Vital Points' and the
requirements which include a waiver making the definition of 'Vital Points' non-
mandatory for aircraft with a Maximum Take-Off Weight Authorised of over
5,700
kg
which were manufactured in accordance with a Type Certificate issued
prior to
1
January
1986.
British Airways should review their Quality Assurance system and the relative
roles of
E1022s
and
QMDRs
be clarified and they should continue to educate and
encourage their engineers
to
provide feedback €tom the shop
floor.
British Airways should review the need to introduce job descriptions/terms of
reference for engineering grades including Shift Maintenance Manager and above.
It
is recommended that British Airways should review the Product Sample
procedure with a view
to
achieving an independent assessment of standards and
conduct an in-depth audit into the work practices at Birmingham.
The CAA should review the purpose and scope of the
FOI
7
Supervisory Visit.
The CAA should consider the need for the periodic training and testing of
Engineers.
The CAA should recognise
the
need for the use of corrective glasses, if
prescribed,
in
association with
the
undertaking of aircraft engineering tasks.
The CAA should ensure that, prior
to
the
issue of an ATC rating, a candidate shall
undergo an approved course which includes training in both the theoretical and
practical handling of emergency situations. This
training
should then be enhanced
at the validation stage
and
later by regular continuation and refresher exercises.
D
F
KING
Inspector of
Air
Accidents
Air
Accidents Investigation Branch
Department
of
Transport
January
1992
The Civil Aviation Authority's response to these Safety Recommendations
is
contained
in
CAA
Follow-up on Accident Reports (FACTAR)
No.
1/92,
to
be published coincident with this
report.
APPENDIX
A
ATC TRANSCRIPT
Doubtful words are indicated by a series
of
question marks. The time signal is shown in
brackets as it occurs in the sequence. There was a slight difference between the time signals at
LATCC and Southampton (SOTON) but it was
of
no significance and has
not
been adjusted.
The
co-pilot was unable to hear the transmissions from LATCC during the descent and before
he had slowed the aircraft to
150
kt at
FL
110,
due to the noisy cockpit environment produced
by
airflow
noise and the captain
flailing
on the outside
of
the aircraft.
To
LATCC
BAW
5390
LATCC
BAW
5390
LATCC
BAW
5390
LATCC
From
BAW
5390
LATCC
BAW
5390
LATCC
BAW
5390
LATCC
BAW
5390
BAW5390
LATCC
LATCC
BAW
5390
BAW
5390
LATCC
Recorded Intelligence
Mayday mayday
-
-
London this is the speedbird five three
nine
zero
mayday mayday mayd-
Speedbird five
three
nine zero Roger mayday acknowledged
out
----
???
???
???
Speedbir-
(0733)
Er
Speedbird five three nine zero
er
confm acknowledge
mayday
Mayday mayday
Er
Speedbird five three nine zero London Control one three
two
d- decimal eight mayday acknowledged
Speedbird five
???
???
zero mayday mayday mayday
emergency depressurisation on a
radar
heading of one nine
five descending to flight level one hundred
Speedbird five three nine zero mayday acknowledged
understand er descending flight level one zero zero on
heading one nine five degrees
(0734)
Speedbird five three nine zero is maintaining one one
zero
-
Speedbird five three nine zero understand maintaining one
one zero
To
From
LATCC PAA 34
PAA 34 LATCC
PAA
34
LATCC
LATCC PAA 34
BAW5390 LATCC
LATCC BAW 218
BAW218 LATCC
LATCC BAW 218
BAW5390 LATCC
BAW5390 LATCC
BAW5390 LATCC
LATCC DAN 231
DAN231 LATCC
LATCC DAN 23
1
Recorded Intelligence
London from thirty
four
would you like
us
to
try
to
relay
thirtytwo eight
Er it's okay Sir
I
think he may be receiving
?
What's that
Thirty
four
er thanks
all
the
same Sir
And Speedbird five three nine zero how
do
you read now
Sir
(0735) Er London Speedbird two one eight
good
morning er
we're descending to flight level two seven zero
Speedbird two one eight
good
morning Sir make your
heading now one one five degrees
and
continue descent
down
to
flight level one one zero to be level abeam Kenet
-
Speedbird two one eight radar heading one one five
descend flight level one
one
zero
to
be
level abeam Kenet
Speedbird five three nine zero London Control how do
you
read
Speedbird five
three
nine zero London Control how do you
read (0736)
Speedbird five three nine zero er London Control how do
you read now
Sir
London Dan' two three
one
good
morning flight level two
nine
zero direct to
Berry
Head
Dan'
two
three one
good
morning
Sir
maintain flight level
two
nine zero
Maintaining two nine zero
two
three
one
To
From
LATCC BAL 224A
BAL224A LATCC
LATCC BAL 224A
LATCC BAL 224A
BAL224A LATCC
BAW5390 LATCC
BAW5390 LATCC
LATCC EIN 522
LATCC BAW 5390
BAW5390 LATCC
BAW5390 EIN522
BAW5390 EIN522
LATCC BAW 5390
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
Recorded Intelligence
'Morning London Britannia
two two
four alfa at three one
eight climbing three
three
zero
direct
Berry
Head
Britannia
two
two
four alfa
good
morning maintain flight
level three
three
zero
on reaching
S-
two two four alfa
wilco
(0737)
Britannia two two
four
alfa's reaching three three zero
Two two four alfa
roger
Speedbird five three nine
zero
London one three
two
eight
(0738)
Er
sorry
station calling
try
again
Er London
the
speedbird five three nine zero's having
problems
???
???
???
???
five three nine zero do you read
Speedbird five
three
nine
zero
read you strength five Sir
go
ahead now
Five three
nine
zero
go
ahead
Five three nine zero
go
ahead London reading
you
London this is speedbird five three nine zero this is er
speedbird five three nine
zero
Speedbird five three nine zero London Control one three two
decimal eight
I
hear
you
strength five Sir
go
ahead now
Roger
Sir we have had an emergency depressurisation and er
requesting radar assistance please for the nearest airfield
(0739)
Er speedbird five three nine zero roger can you accept
landing at Southampton
To
From
LATCC BAW 5390
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
BAW5390 LATCC
LATCC BAW 5390
LATCC RYR
506
RYR506 LATCC
LATCC RYR
506
LATCC BAW 5390
BAW5390 LATCC
Recorded Intelligence
Speedbird er five three nine zero
I
am familiar with Gatwick
would appreciate Gatwick
Er
speedbird five three nine zero roger
if
you make a left
turn
now Sir direct to Mayfeld
-
nine zero
if
you can er direct me into Southampton
affmative
Okay Sir would you prefer Southampton
or
Gat- er Gatwick
Er Speedbird five three nine zero confm you wish
to
route
now
to
Southampton
Speedbird five three nine zero
er
we have (fuselage)
sorry
(heads down)
-
speedbird five three nine zero
-
I
am
maintaining one one zero
I
am at er one fifty knots requesting
radar
assistance into Southampton
Speedbird five three nine zero roger er standby Sir
(0740)
And speedbird five three
nine
zero if you er commence
descent Sir down to flight level seven zero initially
Descend seven zero five three nine zero
London the Ryanair five zero
six
standing by for descent Sir
Five zero six roger cleared down to flight level one one zero
level er by Kenet
-
leaving
two
one zero for one one zero to be level by Kenet
five
-
five zero
six
Confii height cleared
to
Er speedbird five three nine zero you're now cleared down to
flight level seven zero if
you
make one left hand orbit in your
present position please
Sir
be handing you off very shortly
(0741)
To
From
LATCC BAW 5390
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
BAW218 LATCC
LATCC
BAW 218
EIN 602 LATCC
LATCC EIN
602
EIN 522 LATCC
LATCC EIN 522
RYR 506 LATCC
LATCC
BAW 5390
BAW5390 LATCC
LATCC RYR 506
Recorded Intelligence
Cleared to seven zero speedbird five three nine zero
Speedbird five three nine zero continue now with London
Control frequency is one three four decimal four five they
will see you into Southampton
-
four four five thanks very much
Speedbird two
one
eight report your heading now to London
Control frequency is one three
two
decimal zero five
good
hY
One
three
two
zero five with heading speedbird
two
one
eight
good
day
Shamrock
six
zero two contact London Control one three
three decimal four five
good
day
-
Three four five
Shamrock five
two
two contact London one
two
seven
decimal seven
good
day
One
two
seven seven five two
two
(0742)
Ryanair five zero six make your heading now zero nine five
degrees
This is
??? ??? ???
nine zero descending out of eight zero for
seven zero
-
no if you could hold
on
if you could hold onto
him
Er speedbird five
three
nine zero roger remain
on
this
frequency then Sir and
I
will give you radar vectors into
Southampton
-
Er London confm radar heading
zero
nine zero for
Ryanair five zero
six
To
From
RYR506 LATCC
LATCC RYR
506
LATCC BAW 5390
BAW5390 LATCC
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
BAW5390 LATCC
LATCC BAW 5390
BAW5390 LATCC
LATCC
OORDL
Recorded Intelligence
Five zero six make
it
zero nine five please
Zero
nine
five for Ryanair five zero six
Descending
to
seven zero Sir
Five three
nine
zero roger confm you wish to remain on
this frequency
And speedbird five three nine zero continue descent now
down to four thousand feet
London it's speedbird five three nine zero
Speedbird five three nine zero how do you read now sir
Roger reading you er strength five I'm afraid
er
we have
some er debris in the flight deck and er could you confim
the
frequency you changed me
to
(0743)
Okay sir
if
you remain
on
this
frequency sir and continue
descent down to four thousand feet please
Four
thousand feet on QFE confirm QNH confm
Affmative sir
What is the QNH five
three
nine zero
Standby sir
And speedbird five three nine zero
if
you check that now on
er frequency one three one decimal zero Southampton
approach
One three one decimal
zero
bye bye
London oscar oscar romeo delta lima
good
morning
To
From
OORDL
LATCC
OORDL
LATCC
SOTON BAW 5390
BAW5390 LATCC
LATCC
OORDL
BAW5390 LATCC
SOTON BAW 5390
BAW5390 LATCC
BAW5390 LATCC
LATCC BAL 224A
BAL224A LATCC
LATCC BAL 224A
SOTON BAW
5390
BAW5390 SOTON
SOTON BAW 5390
Recorded Intelligence
Oscar oscar romeo delta lima
good
morning sir maintain
flight level eight zero and you can set course from your
present position
-
-
Direct for the bravo romm india
-
Five three nine zero do you read
Five three nine zero read you strength five sir
Oscar delta lima maintaining eight zero and proceeding direct
er bravo romeo india
Er speedbird five
three
nine zero how do you read now sir
(0744)
------
ton it's speedbird five three nine
Z
-
Speedbird five
three
nine zero read you strength five
go
ahead with your message
Speedbird five three nine zero
Er London it's britannia two
two
four alfa er speedbird five
three nine zero's now talking
to
Southampton on
er
one three
one zero
Two
two four alfa roger thanks a
lot
sir
Thank you (0745)
Southampton this is speedbird five three nine zero do you
read (0744)
Speedbird five
three
nine zero
good
morning identified on
hand over London radar six miles
to
the west
of
Southampton airfield what
is
your passing level
Roger sir presently leaving flight level six four could you
confm er your
QNH
please
To
From
BAW5390
SOTON
SOTON BAW 5390
BAW
5390
SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390
SOTON
SOTON BAW 5390
BAW5390
SOTON
BAW5390
SOTON
BAW5390
SOTON
SOTON
BAW
5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON BAW 5390
Recorded Intelligence
Roger my
QNH
one zero one nine millibars the runway in
use is runway zero two the wind is three five zero degrees at
twelve knots
Roger sir
I
am not familiar
with
er er Southampton
I
request
you shepherd me on
to
the runway please (0744:30)
Roger that is copied roll out then on
to
a heading
of
one eight
zero
Radar
heading
of
one eight zero speedbird five three nine
zero
Five three niner zero what is your passing level
Passing level size zero for four zero sir
Thank
you and what is your number
of
persons
on
board
We
have eighty four passengers sir and er
I
think that will be
all
until we're on the ground (0745)
Roger that's copied
And we've been advised that it's pressurization failure is that
the
only
problem
Speedbird five three nine zero
turn
left heading one one zero
Turning left one one
zero
speedbird five
three
nine zero
Five three nine zero we've been advised it's pressurization
failure is that the only problem
Er
negative sir the er captain is
half
sucked out of the
aeroplane
I
understand
I
believe
he
is dead (074530)
Roger that is copied
Er flight attendant's holding on to him but er requesting
emergency facilities for the captain
I
I
I
think he's dead
To
From
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW
5390
BAW5390
SOTON
SOTON G-BS
G-BS
SOTOF
Recorded Intelligence
Roger that is copied continue your descent then at
two
thousand feet
QNH
one zero one niner make
it
a nice gentle
turn
at the moment you're seven miles southwest of the
airfield
Five three niner
er
five three
nine
zero that's affm that's er
ro-radar heading one one zero descending to two thousand
feet
Affirm what is your passing level (0746)
I'm leaving flight er five thousand five hundred feet on ten
nineteen
Roger that's copied give you a little bit more space then
turn
right on
to
a heading of one eight zero
Turning right onto one eight zero speedbird five three nine
zero could you please confirm the
er
the length of your
runway at Southampton is acceptable for er a One-Eleven
(0746:30)
Yes it is acceptable for a One-Eleven and
rll
just give
you
the figures very shortly
Er
as
long as we have
er
at least two and a half thousand
metres
I
am
happy
Er
I',
afraid we don't have two and a half thousand metres
neither do Bournemouth we have a maximum
of
eighteen
hundred metres
Five
three
nine
zero
that is acceptable
Roger that is copied
Bravo sierra
sorry
to interrupt we're at Hurst Castle (0747)
Thank you bravo sierra contact Bournemouth frequency one
one nine decimal
six
two
To
From
SOTON
G-BS
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
UKA455
SOTON
Recorded Intelligence
One
one
nine
six
two
thank you
Speedbird five three niner zero what is your passing level
Speedbird five three nine zero passing level er three eight
fifty
Thankyou
very much continue descent altitude one seven
zero zero feet QNH one zero one niner if
I
turn
you
in
now
you will have fourteen miles is that sufficient
Give me twenty miles speedbird five three nine zero descend
to
er confii level clear
to
(0747:30)
One seven zero zero feet
Cleared to seventeen hundred feet on QFE
Er QFE one zero one seven now
QFE one zero one seven speedbird five
three
nine zero
Five
three
nine zero commence a gentle
left
turn
now then
onto a heading of three six zero
I'll
give you twenty track
miles
to
run for touchdown (0748)
Roger sir
do
you have
an
ILS
frequency
Er negative
I
have a VOR but it
will
be
radar vectors onto the
visual
final
Five three nine zero thank you very much we are three
greens er and flaps forty five
so
I'm set up for an approach
but make it please very gentle
Yes
I
will do indeed you
are
number one in traffic
Five three nine zero thank you
Air
Ukay four five five
are
you with me
To
SOTON
UKA 455
SOTON
UKA 455
SOTON
SOTON
SOTON
From
MAQ 422
SOTON
UKA 455
SOTON
UKA 455
MAQ 422
BAW 5390
BAW5390 SOTON
SOTON
BAW
5390
UKA455 SOTON
SOTON
UKA 455
MAQ422
SOTON
SOTON MAQ 422
MAQ422
SOTON
Recorded Intelligence
Southampton
er
good
morning this is Mac Air four
two
two
er
five zero level er holding over hotel romeo november
(0748:30)
Air Ukay four five five Southampton
Yeah we're fmally levelling six zero on one two zero
Thank
you very much
turn
right now own navigation for
ortac
Ortac ukay four five five request level change one two zero
Southampton er
good
morning rnac
air
four
two
two five
thousand and we're er hotel romeo november (0749)
Speedbird er five three nine zero heading
er
turning er left
onto a heading of due north and levelling
er
eighteen hundred
feet
Thank
you make that one seven zero zero feet on the QFE
one zero
er
one seven
millibars
turn
right heading zero two
five final approach
Descending on
to
seventeen hundred feet and turning right
onto zero
two
five er speedbird five three nine zero
(0749: 30)
Ukay four four four five five contact London frequency one
three four four five
One three four four five cheerio
Mike alfa
kilo
four four two descend altitude
two
five zero
zero QNH one zero one niner
Leaving zero five zero to twenty five hundred feet one zero
one
niner rnac four two two
Four two
two
contact Bournemouth frequency one
two
five
decimal
six
bye bye
To
From
SOTON
MAQ
422
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
BAW5390 SOTON
SOTON BAW 5390
BAW5390 SOTON
SOTON BAW 5390
Recorded Intelligence
Two
two
now
to
one
two five point six
so
long
Speedbird five three nine zero is nine miles from touchdown
you are clear
to
land the wind indicates zero
two
zero degrees
one four knots descend to height one five zero zero feet
on
the
QFE
one zero one seven
Roger
sir
descending to
fifteen
hundred feet
talk
me me
down
all
the way
I
need
all
the
help
I
can get
Roger that is copied
We're running on a heading
of
zero
two
five five five three
nine zero
Roger and er you
will
be able to stop on the runway to
evacuate the aircraft on
the
runway you are number
one
you
are clear to land (0750:30)
Five three nine zero
thank
you very much
Your range now is seven miles from touchdown you're on
the extended centreline
Five
three
nine
zero
thank you very much guidance
all
the
way please
Of course
Your range now is at six and half miles
you
are
clear
to
land
you are on
the
final approach track
Five three nine zero (0751)
Five three nine zero
turn
left five degrees you are five miles
from touchdown continue your descent at the recommended
rate for a three degree glide path (075 1:30)
Roger sir
if
you can er understood
To From
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW 5390
BAW5390
SOTON
SOTON
BAW
5390
Recorded Intelligence
You need not acknowledge further instructions unless
requested it
will
be
an
interrupted
talk
down
but
feel free to
interrupt if you need to you are clear to land four and half
miles on the final approach
track
heading zero
two
zero
Emergency facilities er facilities please er and the ambulance
Everything is available for you
Er five three nine zero thank you
Your range is four miles your height should
be
one
two
five
zero
feet
and the wind is zero
two
zero degrees at one zero
knots (0752)
Five five five three nine zero thank you
Three and a
half
miles from touchdown
turn
right three
degrees on the final approach track heading is
good
Five three nine zero
thank
you
very much
You're lined up you are clear to land
Five three nine zero
You are three miles from touchdown the height should be
nine five er zero feet on a three degree glide path you are
lined
up you are clear to land (0752:30)
Five three nine zero thank you er
I
have the runway
in
sight
Thank
you and you
are
clear to land do you wish me to
continue with further information
Negative
Roger remain on
this
frequency
Five three nine zero
To
From Recorded Intelligence
BAW5390
SOTON
Speedbird five three nine
zero
fantastic
approach you may
shut
down
on the runway
and
leave
the
frequency
SOTON
BAW
5390
Five three nine
zero
thank
you
APPENDIX
B
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~.,*-.-.J
BIRMINGHAM
INTERNATIONAL AIRPORT
-
LAYOUT
APPENDIX
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New
8
UNC
\
Comparison of bolt heads in countersinks
(shown
approximately
1.9
life-size)
APPENDIX
F
PSYCHOLOGIST'S COMMENTS
The human factors issues raised by the fitting of incorrectly sized bolts
to
the windscreen of
this aircraft may be roughly categorised into those directly associated with the individual who
carried out the work, and those associated with the system or environment within which he
operated. These factors are considered in turn.
Factors Associated with the Individual
The errors made by the Shift Maintenance Manager in fitting the windscreen may be listed as
follows
:
a. He failed
to
adopt the ideal procedure of identifying the
type
of bolt
required
by reference
to the illustrated parts catalogue
(IPC),
and its location by reference to the stores computer.
Instead he simply made a match that relied on his own perception of identity between a used
bolt removed from the old windscreen and a new
one
from the parts carousel drawer.
b.
windscreen", and continued to
make
a perceptual match.
He failed to heed the storeman who told him words
to
the effect "They're
8Ds
in
that
c.
In making the perceptual match, he accepted
as
identical two bolts that are different.
d.
fitted bolts left an abnormally large amount of countersink showing once they had been
fitted.
He failed either
to
notice
or
to
question the significance
of
the fact that the incorrectly
e.
He noticed, when fitting a windscreen the following night that
8D
bolts were being used
to
fit
it, believed himself to have used
7D
bolts the previous night, but, even
so,
failed to
question the acceptability of his previous night's work.
Perceptual Problems
The above factors may be split into those in which he made what could be termed poor
judgements
or
work practices and those that involve perceptual errors. Item c, the failure
to
identify the difference between the used
7D
bolt and the new
8C
bolt may reasonably be judged
a perceptual
error.
The Shift Maintenance Manager claims that he made
this
perceptual match accurately in the well
lit stores area
of
the hangar, and noted that
the
used bolt matched with a new size
7D
bolt.
When he came
to
make the match in the poorly
lit
stores of the international pier area, however,
he was content that the used bolt matched a new size
8C
bolt. He claims that he made the
discrimination
in
terms of both sight and touch.
He
held both bolts between
the
forefinger and
thumb of one hand while rolling them between the forefinger and thumb of the other.
The subjective similarity
of
these bolts may
not
be
defined without some form
of
experiment:
it
is fair
to
suggest, however, that they are similar, but not
so
similar that they cannot be
distinguished with reasonable care. The Shift Maintenance Manager does make limited use
of
reading glasses, which appear to
be
of
a fairly weak prescription, but
does
not
habitually use
them at work and was not wearing them
on
this
occasion. Given the poor quality of lighting
in
the pier area stores, he cannot be regarded as having been in the best visual environment
or
possessing the best visual equipment for making
a
visual discrimination that required some
degree of acuity.
Item
d
above may also be regarded
as
a perceptual error
if
he failed to perceive that there was
more countersink than normal showing around the heads
of
the
8C
bolts.
It
is possible,
however, that
he
did notice this, but made what might
be
termed a poor judgement
in
not acting
upon his awareness that the heads looked too
far
down the countersink. The latter possibility
may be regarded as the more likely since, when one of his colleagues spoke with him after the
accident, he claims that he remembered that the countersinks had appeared
too
big
-
ie, he had
noticed extra countersink showing, but interpreted this in terms
of
an
oversize countersink and
not
in
terms
of
an undersize bolt.
Although such
an
interpretation may seemextraordinary,
it
is well documented that individuals
who generate an internal model of
the
world with which they are content often require
overwhelming contradictory evidence before they are prepared to reassess their model. This
tendency may well be exacerbated when the mental resources required for such reassessment
are
limited
by,
for
example, sleep deprivation or circadian
(time
of
day) effects.
The effects
of
time of day
on
many physiological and psychological variables are heavily
researched, the results indicating that the period between 0300 and
0600
is that during which
human performance is at its lowest ebb. It is likely that such time
of
day effects were important
both
in
enabling the Shift Maintenance Manager to fail
to
make accurate perceptual
discriminations, and
in
terms of enabling him to
fail
to appreciate the significance of cues with
which
he
was presented. Direct circadian effects are compounded
in
this instance with some
sleep deprivation. As is common among those on a
first
night shift, he had slept normally the
night before his shift, but slept little during the afternoon before going on shift.
Thus,
at 0300-
0500
he would have had a significant requirement for sleep as well as being at his circadian
low. These factors may reasonably be regarded as combining to exacerbate the effects
described above.
Problems
of
Judgement and Work Practice
Items a, b, and
e
above may
be
regarded
as
problems of poor judgement
or
work practice. The
Shift Maintenance Manager's failure to use the
IPC
and stores computer
to
their best effect, his
failure to
heed
the
storeman's identification of the bolts, and his
failure
to take any retrospective
action when he realised the following day that he was using bolts
of
a different size from those
he had used on the same job the previous day, lead to the conclusion that he was not working
with the degree of care that the job demanded. What is less clear, however, is whether he was
doing the job in a way that he regarded as being of a standard acceptable
to
the system within
which he was working,
or
whether he knew that his work practices left a good deal to be
desired, but chose to ignore this knowledge in the interests of expediency.
A clue to the solution may be found in the Shift Maintenance Manager's other behaviour and in
the opinions of his colleagues.
A
consistent picture emerges from such considerations. He
appears
to
be regarded as solid and careful by others, and this assessment seems substantiated
by his behaviour on the night in question. Although his shift did not start until
1030,
he was at
work
45
minutes early in order to prepare himself and
to
get the work
of
his shift organised.
He also continued
to
work through his meal break. At interview he does not give the
impression of one who would take his responsibilities lightly, or behave in a way that he would
consciously appreciate as derelict. One is left with the impression that the Shift Maintenance
Manager behaved in a way that he felt was appropriate
to
the circumstances in which he found
himself. Overall, his approach to the job could be summarised as conscientious but pragmatic,
rather than conscientious and meticulous.
A
good example
of
this approach concerns his
decision
to
torque the windscreen bolts to
20
lbf in instead
of
the specified
15
lbf in. He
plainly did not do this as a matter of expediency, but because he felt that this was a better way
to do the job. What was missing was an appreciation that such individual work practices are
completely out of place in aircraft servicing.
This impression is reinforced by conversation with other shift supervisors. At informal
interview, these individuals gave the general impression
of
being free to tackle jobs
in
idiosyncratic ways, and when informed of the manner in which the Shift Maintenance Manager
behaved on the night in question they did not (except one individual) regard this as
unreasonable
or
demanding of censure.
It
does not seem unreasonable
to
suggest that the
general climate in the maintenance facility at Birmingham was not one in which the care and
safety awareness exhibited by the staff matched the criticality
of
the
task. The nature of the
maintenance operation at Birmingham and
the
setting and checking of operational standards
is
therefore examined below.
The Operating Environment
Inspection
A procedure included in many industrial operations that have safety implications is that of
independent inspection
of
work. It is possible that independent inspection would have
prevented this accident since
the
poor
fit
of the bolt heads
in
the countersinks was potentially
observable. There
are
some more important general
points
that may be made about the utility of
inspection
in
safety critical systems:
a. Independent inspection does not have a small effect on the possibility
of
a maintenance
error, going undetected, but reduces it dramatically. If an individual operator has, say, a
.01
chance of not noticing a fault, then the combined probability of two such individuals failing to
notice the fault becomes only
.OO01.
b. If an individual has made an error in work that he has carried out, then (because he has
developed a perceptual "set")
he
is less likely to detect that error than an individual who comes
to the task both afresh and in a "checking" frame of mind.
c. The knowledge that work is to be inspected may change the approach of an operator
to
his task.
It
could
be
argued that the operator would become less careful
if
he felt that inspection
would pick up his errors, and would make him feel less trusted and responsible. For
individuals with some pride
in
their work, however, the knowledge that their work was
to
be
inspected might well make them more careful since they would not wish
to
be found to have
made a mistake.
e. Inspection is likely to have a general effect on the individual operator's perception of the
standards and care expected of him by the system. Inspection of work may serve as a regular
reminder to operators that the work they carry out has safety importance, and must be carried
out
meticulously.
It
is likely that an operator will perceive the absence of inspection as an
indication that the managers
of
the system regard the cost saving involved as more important
than
the
safety benefit, and this may well influence
the
Shift Maintenance Manager's general
approach to
his
task.
It is thus suggested that inspection represents an important addition
to
the maintenance work
practices evident in this accident, and that it is especially important for work carried out at
night, when errors are more likely to be made, and less likely
to
be detected by their
perpetrators.
Lastly,
it
is interesting to note
in
this context that had this windscreen been changed
in
the
Royal Air Force, not only would the work have been inspected, but the aircraft would have
been pressure tested on the ground before flight.
Maintenance of Standards in Working Practices
There appears to be a stark contrast between the procedures adopted to ensure that pilots adhere
to standard operating procedures and to ensure that they are familiar with
good
working
practice and those adopted for maintenance personnel. Although the maintenance environment
is checked periodically to ensure, for example, the calibration of equipment and currency of
technical information, there does not appear to be any checking of
the
knowledge of,
or
techniques used by, the engineers. In the absence of such checks, and in the apparent absence
of any courses, instruction, or training designed to ensure that aircraft engineers appreciate
the
importance of standardised procedures, a meticulous approach to the job, and the consequences
of
error, it should not perhaps be regarded as surprising that experience and familiarity tend to
dull the engineer's conscious appreciation of the critical nature of his task.
It
seems that the system operated at Birmingham relied entirely on the "professionalism"
of
individual shift supervisors
to
ensure that working practices were appropriate. Whereas
it
is
entirely right to expect a professional approach from such individuals, the wisdom of leaving
the safety of aircraft entirely to individual judgement without having any systems for
maintaining consistency
or
for checking that high standards are maintained must be
questionable.
Design Safety
It
is obviously highly undesirable that this windscreen assembly should have been designed
such that
it
could be
fitted
with bolts that were very similar to the correct ones, that could be
inserted and engage with
the
anchor
nuts,
and yet which failed as soon as they were loaded.
It
is not asking too much for considerations such as this to be made during design, but the
awareness that this type of problem is best obviated at the design stage was not widespread
when this aircraft was conceived. It could
also
be argued that this windscreen should have
been designed
to
be fitted as a plug from the inside
of
the
aircraft
-
an
obviously safe practice in
a pressurised hull.
Poor
design is further evidenced by the fact that this
aircraft
was already
fitted
with the wrong
bolts (7Ds instead of
8Ds)
in
the old windscreen. This is probably because the
No
1
and
No
3
windscreens
are
fitted with bolts of slightly different lengths, yet only the shorter bolt is
actually illustrated in the
IPC.
It is difficult
to
believe that it would not have been easily
possible for these windscreens to have been designed
so
that they were both
fitted
with the
same size of
bolt.
When a new windscreen is fitted,
it
is customary
for
the engineers
to
fit
new bolts only if those
removed were damaged or paint clogged. The relative cost
of
bolts and windscreen might
suggest, however, that it would not be unreasonable for new bolts
to
be fitted whenever a
windscreen was changed. If this were
so,
the windscreen could be supplied as a
kit
with a set
of
correct bolts included.
It may
also
be observed that, once the type of bolt used on this windscreen is removed from its
packet,
it
carries no identifier, compelling
it
to
be identified by
its
physical characteristics.
It
is
possible that if its head were stamped with such an identifier
(eg
8D),
then the Shift
Maintenance Manager may have used this instead
of
relying on a physical comparison.
Printed
in
the
United
Kingdom
for
HMSO
Dd294964 3/92
C6
G3390 10170
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the United Kingdom the responsible
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