Kegworth Air Crash Investigation

Car Accident - Kegworth Air Crash Investigation

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Kegworth 1989: an accident waiting to happen?

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On January 8, 1989, habit domestic flight 092 was enroute from London Heathrow airport to Belfast in Northern Ireland. It was the second flight undertaken by the British Midland Boeing 737-400 that day and the aircraft was close to its landing destination when a composition of mechanical and human error led to disaster.

Preparing to land at the East Midlands airport, the aircraft (tail marked G-Obme) plummeted onto an embankment of the M1 motorway near Kegworth, Leicestershire, killing 47 people and seriously injuring a further 74, along with seven members of the flight crew.

In summarising the cause of the accident, The Aircraft accident narrative stated "The cause of the accident was that the operating crew shut down the No.2 machine after a fan blade had fractured in the No.1 engine. This machine subsequently suffered a major thrust loss due to secondary fan damage after power had been expanding during the final approach to land" (Aaib 1980, 35). This much is unmistakably true, however it was a composition of errors, mechanical, procedural and cognitive, which finally caused the aircraft to fail during its final landing phase.

In order to extrapolate the events of that day it is primary to seek a chain of events rather than to study each constituent error or malfunction in turn. As is often the case with aircraft crash investigation, a sequence of human and operational errors tends to yield a domino effect in which it is the inertia of one event beyond another that results in a catastrophic end (Job,1996; 173). The chronology of these events is therefore particularly foremost in helping to analyse the failure chain that led up to the crash.

G-Obme was engaged on a duplicate shuttle run between London Heathrow airport and Belfast Aldergrove Airport. The first leg of the journey was uneventful. during the second leg of the shuttle the aircraft climbed initially to six thousand feet where it levelled-off for about two minutes before receiving clearance to climb to a flight level of twelve thousand feet. At 7.58 p.m., clearance was given to climb to thirty five thousand feet. At 8.05 p.m. As the aircraft was climbing through flight level 283 the crew experienced severe vibration and a smell of fire. No fire warnings, optical or audible were alerted by instruments on the flight deck. A later replay of the Flight Data Recorder showed that severe vibrations had occurred in the No.1 (left) engine, together with indications of an erratic fan speed, a rise in exhaust temperature and a low, variable fuel flow (Aaib, 1980; 145).

Captain Hunt took operate of the aeroplane and disengaged the autopilot. He later claimed that the machine instrumentation did not give him any clear indication of the source of the malfunction. He also later stated that he understanding that the smoke was coming forward from the passenger cabin which, from his comprehension of the 737's air conditioning system, led him to believe that the smoke was in fact coming from the No 2 (right) engine. Consequently the command was issued to throttle back the No.2 engine. As a effect of this course the aircraft rolled gradually to the left through sixteen degrees but the commander made no corrective movements of either rudder or aileron.

The commander later claimed that reducing the throttle of No.2 machine reduced the smell and signs of smoke and but he later remembered that the primary vibration prolonged after the No.2 throttle was closed.

After throttling back the No.2 engine, London Air Traffic operate were immediately advised of an accident situation with appeared to be an machine fire. Forty-three seconds after the onset of the vibration the commander ordered First Officer McClelland to "shut it down". The shut down was delayed at the First Officer responded to radio messages from London Air Traffic operate request which alternative airport they wished to land at. Shortly after shutting down No.2 machine Bma Operations requested the aircraft divert to the East Midland Airport (Aaib,1980; 40).

As soon as the No.2 machine had been shut down, all evidence of smoke cleared from the flight deck which further convinced the Commander that he had made the literal, decision, not least in that No.1 machine showed no signs of malfunctioning and prolonged to operate albeit at reduced power and with increased fuel flow.

Passengers were aware of smoke and of smells similar to "oil" or "rubber" in the cabin. Some passengers saw evidence of fire from the left engine, and several cabin attendants saw fire from the No.1 machine as well as light coloured smoke in the cabin.

Despite indication that the fire was emanating from the other machine neither passengers nor cabin crew alerted the flight crew to this fact. This may have been due to general obscuring at the time, allied with a reliance that the pilot finally knew what he was doing.

At 8.20 p.m. At a height of three thousand feet power was increased on the No.1 engine. The aircraft was then cleared to descend to two thousand feet and, after joining the centre line at two thousand feet above ground level (agl) the Commander called for the landing gear to be lowered and fifteen degrees to be applied to the flaps. At nine hundred feet there was a sudden decrease in power from the No.1 engine. As the aircraft dipped below the glidepath and the ground presence warning system (Gpws) sounded the Commander broadcast "prepare for crash landing" on the cabin address system. The aircraft hit the ground at 8.24 p.m. At a speed of 115 knots.

One survivor, Gareth Jones, described the moment when the plane hit the ground as follows: "There was a shudder, crash, like a immense motor car accident, crunch, blackness, and I was by the accident hatch." (Bbc, 1989).

The Aaib narrative (Aaib, 1980; 35) concentrated upon the failure of the flight crew to respond accurately to a malfunction in the estimate 1 engine, and highlighted the following operational errors:

1. The composition of machine vibration, noise and the smell of fire were covering their training and expertise.

2. They reacted to the preliminary machine qoute prematurely and in a way that was contrary to their training.

3. They did not assimilate the indications on the machine instrument display before they throttled back the No.2 engine.

4. As the estimate 2 machine was throttled back, the noise and shuddering associated with the surging of the No.1 machine ceased, persuading them that they had correctly identified the defective engine.

5. They were not informed of the flames which had emanated from the No.1 machine and which had been observed by many on board, along with 3 cabin attendants in the aft cabin.

Many accident reports cite human failure as a customary cause (Johnson, 1998).
However, before finding at the certain failure in Captain Hunt's inability to decree which of the 737's engines had unmistakably malfunctioned, attention should be drawn to the faulty machine itself. The actual cause of the malfunction was a broken turbine, itself the effect of metal fatigue caused by inordinate vibration.

The upgraded Cfm56 machine used on the 737-400 model were subject to inordinate amounts of vibration when operating at higher power settings over twenty five thousand feet. Because this was an upgrade to an existing engine, the machine had only ever been tested in a laboratory, not under actual flight conditions. When this fact was subsequently discovered colse to a hundred 737-400's were grounded and the engines subsequently modified. Since the Kegworth crash all significantly redesigned turbofan engines must be tested under actual flight conditions. Arguably then, the inadequately tested Cfm56 machine on flight 092 may have been "an accident waiting to happen" (Owen, D. 2001; 132).

The Aaib narrative ended that the composition of machine vibration, noise and the smell of fire were covering the flight deck crew's area of expertise. (Aaib, 1980). This may or may not be a fair estimation since few pilot's and First Officer's fortunately ever experience the actual effects of smoke and fire while in command.

Whilst simulators can help train for accident procedures it is questionable how primary such procedures may be, particularly if the crew have not been thoroughly trained on the unique procedural and technical requirements complicated in flying a singular aircraft variant. Significantly, the flight crew of 092 had microscopic reliance in the accuracy of key instrumentation along with vibration meters.

Dr Denis Besnard of Newcastle university analysed the Kegworth air crash, terminal "The pilots of the B737 were caught in what is known as a confirmation bias where, instead of finding for contrary evidence, humans tend to overestimate consistent data. people overlook and sometimes unconsciously disregard data they cannot explain" (Besnard D, 2004; 117).

"Confirmation bias", i.e. The overloading of consciousness by a quantity of bewildering or conflicting data was also established as a customary cause of the crash when investigated by a study team from the University of York and the University of Newcastle upon Tyne. The seminar that people tend to over simplify complicated situations particularly during accident has been is both well documented and primary in the causation of the Kegworth air crash (Besnard. D., Greathead, G. & Baxter, G, 2004; 117-119).

Specifically, Captain Hunt had not received training on the new model 737-400 since no simulators for this variant existed in the Uk at that time. This is both imaginable and primary when inspecting the following points. The captain believed the right machine was malfunctioning due to the smell of smoke, maybe because in former Boeing 737 models the air for the air conditioning system was taken from the right engine.

However, starting with the Boeing 737-400 variant, Boeing redesigned the system to use bleed air from both engines. Captain Hunt would have been unaware of this fact, which formed a primary part of his decision to shut down the wrong engine. This would prove disastrous.

Apart from the coincidence of the smoke vanishing when the auto-throttle was disengaged, the pilots may have also been in the habit of disregarding the readings of vibration warning meters, since early ones were perceived to be unreliable. The crew of G-Obme do not seem to have been aware that newer ones were, however, more reliable. Should more attention have been paid, therefore, to vibration issues rather than to smoke and the smell of fire, events may well have transpired very differently on the evening of January 8th (Owen, 2001; 131-2).

Subsequent study has critically ended that "organisational failures generate the primary preconditions for human error" and "organisational failures also exacerbate the consequences of those errors" (Stanton, 1994; 63). The Kegworth air crash was therefore the effect of a sequence of failures originating from a mechanical defect.

Additionally, cognitive error on the part of the flight crew enhanced by inadequate flight training compounded the error chain. finally the flight crew did not verify their interpretation of events by consulting with cabin staff or passengers even though data to advise the fault lay with the other machine on the aircraft was ready at the time.

Bibliography

Bbc (1989) On This Day: Dozens die as plane crashes on motorway. [online] ready from http://news.bbc.co.uk/onthisday/hi/dates/stories/january/8 [accessed 2 March 2007]

Besnard, D. (2005) International Aviation and Fire protection Association. [online] ready from http://www.iafpa.org.uk/news-template.php?t=4&id=1312 [accessed 1 March 2007]

Besnard, D., Greathead, G., and Baxter, G., (2004) International Journal of Human-Computer Studies. When reasoning models go wrong. Co-occurrences in dynamic, primary systems, Vol. 60, pp. 117-128.

Job, M. (1996) Air Disaster Volume 2. Pp. 173-185. Aerospace Publications Pty Ltd

Johnson, D. 1988; University of Glasgow agency of Computing Science (1980) Visualizing the association between Human Error and Organizational [online] University of Glasgow, 1980. Http://www.dcs.gla.ac.uk/~johnson/papers/fault_trees/organisational_error.html [accessed 2 March 2007]

Owen, D. (2001) Air accident Investigation, 1st ed., Ch. 9, pp. 132-152. Sparkford, Patrick Stephens Limited

Stanton, N.A., (1994) The Human Factors of Alarm Design, Ch. 5, pp. 63-92. London, Taylor and Francis Ltd

United Kingdom. Air Accidents Investigation subject (1990) Boeing 737-400, G-Obme, near Kegworth, Leicestershire 8th January 1989, estimate 4/90. London, Hmso.

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