|University of Bielefeld - Faculty of technology|
Networks and distributed Systems
Research group of Prof. Peter B. Ladkin, Ph.D.
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|This page was copied from: http://www.open.gov.uk/aaib/gobme/a6.htm|
ACCIDENT TO BOEING 737-400 G-0BME AT KEGWORTH,
LEICESTERSHIRE ON 8 JANUARY 1989
This bulletin contains a statement of the
facts which have been determined up to the time of issue. It
is published under Regulation 6 of the Civil Aviation (Investigation
of Accidents) Regulations 1983 to inform the aviation industry
and the public of the general circumstances of the accident.
It must necessarily be regarded as tentative, and subject to alteration
or correction if additional evidence becomes available. The bulletin
is not an accident report - either final or interim.
On the 8 January the Chief Inspector of Accidents
appointed Mr E J Trimble, a Principal Inspector of Accidents,
to carry out an "Inspector's Investigation" in accordance
with the regulations. Much work remains to be done before his
report can be compiled. Following this he, as the Inspector,
must invite and consider representations on the draft report from
the parties involved (in accordance with Regulation 11) before
it is completed for submission to the Secretary of State for Transport.
Unless one of these parties asks for a Review Board (under Regulation
12) the report will then be published.
Thus nothing in this bulletin is to be taken
as a final statement of the facts and circumstances of the accident,
nor would it be right to draw any conclusions from it as to the
cause(s) of the accident.
This bulletin can be reproduced without specific
permission providing that the source is acknowledged.
|Aircraft type and Registration||Boeing 737-400, G-OBME|
|No & Type of Engines||2 CFM 56-3C high by-pass turbo-fan engines|
|Year of Manufacture||1988|
|Date and Time (UTC)||8 January 1989 at 2025 hrs|
|Location||Kegworth, near East Midlands Airport, Leicestershire|
|Type of Flight||Scheduled passenger|
|Persons on Board||Crew 8 - Passengers - 117 + 1 infant|
|Injuries||Crew 7 (Serious) - Passengers 47 (fatal)|
|Passengers 66 + 1 infant (serious)|
|Crew 1 (minor) - Passengers - 4 (minor)|
|Nature of Damage||Aircraft destroyed|
|Commander's Licence||Airline Transport Pilot's Licence|
|Commander's Age||43 years|
|Commander's total Flying Experience||13180 hrs (of which 765 were on Boeing 737-300/400 types)|
|Information Source||AAIB Inspector's Investigation under the Civil Aviation (Investigation of Accidents) Regulations 1983)|
History of the flight
The aircraft was engaged on a double shuttle between London Heathrow
and Belfast. It landed at Heathrow at 1845 hrs after completing
the first shuttle flight and took off again for Belfast at 1952
hrs with the first officer handling the aircraft. After take-off,
the aircraft climbed initially to flight level (FL) 60, where
it levelled off above a layer of stratocumulus cloud for two minutes,
before receiving clearance to climb to FL 120. Soon afterwards,
at 1958 hrs, clearance was passed for the aircraft to continue
its climb to its cruising FL of 350 on a direct track to the Trent
VOR (Very high frequency Omni-Range beacon).
At 2005.05 hrs, as the aircraft was approaching FL 290, the flight
crew experienced moderate to severe vibration, a burning smell
and smoke. The commander immediately took control of the aircraft,
disengaging both the auto-pilot and the automatic throttle. The
two pilots then diagnosed the symptoms of vibration and smoke
as indicating a problem in the right engine and 20 seconds after
the onset of the vibration, the commander instructed the first
officer to throttle back the right engine. The commander later
stated that the action of closing the right throttle reduced the
smell and signs of smoke and that he remembered no continuation
of the vibration after the right throttle was closed.
Immediately after throttling back the right engine, the first
officer advised London Air Traffic Control (ATC) that the aircraft
was at FL 300 and that they had an emergency situation which looked
like an engine fire. When this message had been passed, the commander
ordered the first officer to shut-down the engine; the flight
crew were then engaged in ATC radio transmissions, stating their
intention to divert to Castle Donington (East Midlands Airport).
During this period a female cabin attendant used the cabin address
system to advise the passengers to fasten their seat belts. The
right engine was shut down 2 minutes and 7 seconds after the vibration
began. By that time power had been reduced on the left engine,
which continued to operate at comparatively low power. After
the accident, the commander stated that during the remainder of
the descent the indications from the engine instruments were such
as to confirm that the emergency had been successfully concluded
and that the left engine was operating normally. The recorded
engine parameters associated with this stage of the flight are
included in the section on "FDR and CVR evidence".
In the cabin, the passengers and the cabin attendants had heard
an unusual noise accompanied by moderate to severe vibration.
Some passengers had also been aware of what they described as
smoke, but none were able to describe its colour or density.
They described the smell of burning as "rubber", "oil"
and "hot metal". Many had seen signs of fire from the
left engine, which they described variously as "fire",
"torching" or "sparks". Several of the cabin
attendants described the noise as a low, repetitive "thudding",
and one described how the vibration had been severe enough to
shake the walls of the forward galley. Soon after the right engine
had been shut-down, and in response to a cabin "chine"
from the commander, the flight service manager (FSM) came to the
flight deck. The commander asked him if they had had smoke in
the cabin. He replied that they had. Later, after another statement
from the FSM that the passengers were becoming concerned, the
commander broadcast on the cabin address system that there was
trouble with the right engine which had produced some smoke in
the cabin, that the engine was not shut-down and that they could
expect to land at East Midlands Airport in about 10 minutes.
Passengers stated that the smell of smoke had dissipated by the
time the commander made this announcement.
The right engine had been shut-down approximately 5 nm north-west
of East Midlands Airport. Having cleared the aircraft to turn
right and descend to FL 100, London ATC passed control to Manchester
ATC, who passed headings for the aircraft to descend to the north
west of East Midlands Airport, before vectoring it to the east
of the airport to begin its approach to runway 27. ATC control
of the aircraft was then transferred to Castle Donington Approach.
The approach then continued until the aircraft was on the localiser
of the instrument landing system (ILS) for runway 27, with flaps
lowered to 5°. At 2,000 ft the landing gear was lowered
and, as the outer marker was passed at 4.3 nm from touchdown,
15° of flap was selected. One minute later, at 2023.50 hrs,
when the aircraft was 2.4 nm from touchdown and at a height of
900 ft above ground level (agl), the left engine lost power with
compressor speed reducing rapidly and high vibration levels.
The commander told the first officer to relight (ie restart) the
right engine. 17 seconds after the power loss, the fire warning
system operated on the left engine. No power became available
from the right engine before the aircraft struck the ground at
2024.43 hrs, 36 seconds after the fire warning.
The initial ground impact was in a nose-high attitude on level
ground just to the east of M1 motorway. The aircraft then passed
through trees and suffered its second, and major, impact on the
western (ie northbound) carriageway of the M1 and the lower part
of the western embankment: this second impact occurred some 70
metres after the initial impact and 10 metres lower. The fuselage
was extensively disrupted and the aircraft came to rest entirely
on the wooded western embankment, approximately 900 metres from
the threshold of runway 27 and displaced 50 metres to the right
of the centreline of the approach lights.
Ground witnesses who saw the final approach of the aircraft saw
clear evidence of fire associated with the left engine. The intake
area of the engine was filled with yellow/orange fire and flames
were observed streaming aft of the nacelle, pulsating in unison
with "thumping noises" which emanated from this engine.
Metallic "rattling" noises were also heard and flaming
debris was observed falling from the region of the burning engine.
Examination of the fuselage showed that two major structural failures
had occurred in the impact, one slightly forward of the wing leading-edge
and one aft of the wing trailing-edge. These had respectively
resulted in the fuselage nose section becoming detached from the
centre section and the tail section buckling over, and to the
right of, the centre section. The forward fuselage had therefore
sustained a high degree of disruption in the passenger cabin,
with floor structure, seats and furnishings becoming detached;
similar damage had occurred around the aft fuselage failure.
The floor structure and seating were much less disrupted in the
centre (ie over-wing) section of the cabin and in the inverted
The Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR)
were removed during the early morning of Monday 9 January and
taken to AAIB Farnborough for readout and analysis.
The No 1 (left) engine showed evidence of fire damage, including
that arising from ground fire. The left wing appeared to have
contained its fuel, whereas the right wing had suffered sufficient
impact damage to cause leakage of its fuel contents, which had
run back down the embankment slope, on to the motorway.
The No 2 (right) engine showed no evidence of fire.
Fragments of engine fan blades from No 1 engine were found under
the approach path, up to 31/2 km east of
the crash site.
The airframe wreckage was progressively removed from the site
and transported to AAIB Farnborough during the period from 10-14
January and the engines were transported directly to the manufacturer,
CFMI at Villaroche in France on 13-14 January where they were
the subject of detailed strip down examination, under AAIB supervision.
FDR and CVR evidence
The aircraft was equipped with a Sundstrand Universal Flight Data
Recorder and a Fairchild A100 Cockpit Voice Recorder. Both were
replayed satisfactorily at AAIB. The FDR read-out established
that, as the aircraft was approaching FL 290, an event occurred
which led to the No 1 (left) engine recording its maximum indicated
vibration level ("5 units"), recordings of rapidly fluctuating
fan speeds and fluctuating HP core speeds, with an associated
rise in exhaust gas temperature (EGT) and fluctuation in fuel
flow. Approximately 20 seconds after this occurrence, the No
2 (right) engine was throttled back, at which point the No 1 engine
fan and core speeds settled down, although at slightly different
values, with the indicated vibration level remaining at maximum
and EGT markedly higher than before - ie 840°C, compared
to 780°C previously. Prior to being throttled back, the
No 2 engine had been operating with steady engine indications,
with a fan speed (N1) of 99%, HP compressor speed (N2) of 96%,
EGT of 770°C and low vibration level ("0.5 units").
1 minute and 47 seconds later, the No 2 engine was shut-down.
It was apparent that the flight crew were aware of smoke on the
flight deck and thought that they had a possible engine fire.
There was no fire warning at this time.
The flight proceeded under the control of London, Manchester,
and finally Castle Donington ATC. The No 1 engine appeared to
respond reasonably to applied throttle demands, although the engine
was at "flight idle" for a considerable time (10 minutes).
At about 900 ft above ground level on the final approach, the
No 1 engine fan speed dropped rapidly and EGT increased significantly
with other engine parameters unchanged, and a maximum indicated
vibration level. The No 1 engine lost considerable power and
some 17 seconds later the fire warning bell sounded. About 36
seconds later the aircraft impacted with the ground.
Engine strip examination
Inspection of the fan assembly of the No 1 (left) engine showed
extensive damage had occurred to the titanium alloy blades, with
many associated damage-induced overstressing failures. One fan
blade was found to have fractured outboard of the "mid-span
shrouds", due a progressive fatigue failure originating near
the leading edge of this blade, adjacent the pressure face. This
failure had released the outer "panel" (Approximately
4 inches) of this blade. The cause of this fatigue failure, which
was the only instance of fatigue fracture found amongst the fan
blades, is being pursued.
The abradable seal material which surrounds the fan assembly would
have been progressively removed by the damaged fan assembly, as
would the rubberised seals surrounding the low pressure compressor
"booster" section, due to out-of-balance running, and
would have led to associated smoke products entering the air conditioning
Inspection of the No 1 engine revealed evidence consistent with
the anticipated effects of this engine having run under severe
out-of-balance conditions due to fan damage, with some damage
to the high pressure compressor arising from fan debris ingestion.
No failures were found within the coremodule rotating assemblies.
Investigation of the source(s) and development of the airborne
fire on the No 1 engine is still in progress. Evidence found
to date is provisionally indicative of two areas of fire, one
of which was located around the upper/outboard region of the exterior
of the fan casing and the other which appears to have trailed
from the thrust reverser duct on the left side. It is considered
that the sources of both areas of fire were secondary to, and
were induced by, the primary engine failure and subsequent continued
operation with attendant high vibration.
Detailed investigation of the No 1 engine and its operating history
will continue in an attempt to identify the cause of the fan blade
fatigue and to explain fully the initiation and progression of
The No 2 (right) engine has been fully stripped and shows no evidence
of pre-crash fire of failure.
Checks have been made of the wiring leading to the Engine Indicating
System (EIS). These have confirmed that the indications of both
primary and secondary engine parameters were displayed in the
correct sense. The primary EIS display unit passed a full function
and calibration check. The secondary EIS unit exhibited an obvious
fault condition affecting the display of oil pressure, hydraulic
pressure and oil quantity, but not the engine vibration indicators.
The secondary EIS unit had suffered significant impact damage
and the fault appears consistent with such damage. Since the
Flight Data Recorder receives engine data (except vibration) from
the EIS output to its display, it is implicit that such data was
displayed by the EIS.
The Airborne Vibration Monitor unit (AVM), which feeds vibration
signals from the engines to the EIS and FDR, was subjected to
a full test schedule and, despite some minor external case damage,
fully met the acceptance requirements. Both engine vibration
indicators operated satisfactorily. The engine vibration indicators
and FDR cannot register vibration levels higher than "5 units",
since the AVM limits its output.
The Engine and APU fire detection module was severely damaged
by impact, such that a functional test was not possible, and will
require detailed inspection. Checks of the actual detector loops
on the engines concluded that those not damaged beyond meaningful
test by impact were capable of providing both overheat and fire
detection warnings. The Engine and APU fire suppression bottles
were found fully charged. There were no indications that an attempt
had been made to discharge any extinguisher.
Further investigation of the systems aspects will include an appraisal
of the EIS/Flight crew interface to evaluate the effectiveness
of the presentation of engine indications to pilots. This evaluation
will be assisted by the RAF Institute of Aviation Medicine Flight
A full evaluation of passenger and crew testimony and injury,
combined with an analysis of the pathology, is being progressed.
This information will be related to the crash-induced damage
to the cabin structure and seating in order that the causes of
injury are identified, with a view towards consideration of what
improvements may be indicated to reduce injuries and maximise
survivability in future accidents.
AAIB Safety Recommendations
Shortly after the accident, on the 11 January 1989, AAIB made
2 Safety Recommendations to the CAA. These were made at a stage
in the investigation when it was known that the left engine had
failed in-flight, but the reason for the in-flight shut-down of
the right engine had not yet been established. In addition, it
was considered prudent to address the possibility of a defective
engine vibration or fire/overheat warning system although no evidence
of such defect(s) had been found. The following precautionary
Safety Recommendations were made to the CAA:
|1.||That the CAA consider increasing the frequency of existing engine inspections and engine health monitoring on Boeing 737-300 and Boeing 737-400 aircraft until the causes of the engine failure(s) are established.|
|2.||The CAA call for an examination of the Boeing 737-300 and Boeing 737-400 engine Fire/Overheat and Vibration monitoring circuitry for left/right engine sense.|
As a result, the CAA issued letters to owners/operators Nos 905
and 906 on 11 January 1989 which required (respectively) testing
of the engine overheat/fire warning and vibration monitoring systems
for "correct-sense" operation; and increased frequency
of certain engine "health monitoring" checks on Boeing
737-300, 737-400 and Airbus 320 aircraft.
On 10 February 1989, the AAIB advised the CAA that the left engine
had suffered a fatigue-failure of a fan blade and that there was
no continuing justification for the increased inspections of the
"oil-wetted" components of the CFM 65-3 and -5 engines.
However, in view of the fan blade failure (the cause of which
has not thus far been established) and AAIB caution concerning
any possible means by which the fatigue strength of such fan blades
may be inadvertently compromised, the following 2 Safety Recommendations
were made to the CAA:
|3.||The Civil Aviation Authority, in conjunction with the engine manufacturer, consider instituting inspection procedures for the examination of the fan stage of CFM 56 engines to ensure the early detection of damage that could lead to the failure of a blade.|
|4.||The Civil Aviation Authority review the advice given in the Boeing 737-400 Maintenance Manual concerning the excessive generation of heat during blending operations with power grinding and blending tools.|
CFMI and Boeing issued letters to operators, emphasising the daily
visual check on the engine inlet and fan blades and the detailed
fan blade inspection at the aircraft "B check" (approximately
every 750 hours). In addition, operators were recommended to
review their policies and instructions for the maintenance and
repair of CFM 56 fan blades, with particular emphasis on adhering
strictly to the limits and procedures detailed in the aircraft
maintenance manual for fan blade repair.
On 23 February 1989, the AAIB made a further 3 Safety Recommendations
to the CAA:
|5.||The CAA take action to advise pilots of Boeing 737-300/400 aircraft, and of other types with engines which have similar characteristics, that when instances of engine-induced high vibration occur, they may be accompanied by associated smoke and/or smells of burning entering the flight deck and/or cabin through the air-conditioning system, due merely to blade tip contact between fan/compressor rotating assemblies and the associated abradable seals.|
|6.||The CAA request the Boeing Airplane Company to produce amendments to the existing aircraft flight manuals and checklists to indicate what actions should be taken when engine-induced high vibration occurs, accompanied by smoke and/or the smell of burning entering the flight deck and/or cabin.|
|7.||The CAA review the current attitude of pilots to the engine vibration indicators on Boeing 737-300/400 aircraft and other applicable types with turbo-fan engines, with a view towards providing flight crews with an indication of the pertinence of such vibration instruments when certain engine malfunctions or failures occur.|
|This page was copied from:||http://www.open.gov.uk/aaib/gobme/a6.htm|