Kegworth air disaster
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The scene of the disaster, with the runway that G-OBME failed to reach at the top of the picture.
|Date||8 January 1989|
|Summary||Engine fan blade fracture (design flaw)|
|Site||Kegworth, Leicestershire, England
|Aircraft type||Boeing 737-400|
|Flight origin||London Heathrow Airport|
|Destination||Belfast International Airport|
The Kegworth air disaster occurred when a Boeing 737-400 crashed on to the embankment of the M1 motorway near Kegworth, Leicestershire, England, while attempting to make an emergency landing at East Midlands Airport on 8 January 1989.
British Midland Flight 92 was on a scheduled flight from London Heathrow to Belfast, when a fan-blade fractured in the left engine, disrupting the air-conditioning and filling the flight-deck with smoke. The pilots believed that this indicated a fault in the right engine, since earlier models of the 737 ventilated the flight-deck from the right, and they were unaware that the 400 used a different system. So they mistakenly throttled back the good engine, pumping more fuel into the malfunctioning one, which burst into flames. Of the 126 people aboard, 47 died and 74 sustained serious injuries.
The enquiry attributed the blade fracture to metal fatigue, caused by heavy vibration in the newly upgraded engines, which had only been tested in the laboratory and not under representative flight conditions.
The aircraft was a British Midland-operated Boeing 737-400, registration G-OBME, on a scheduled flight from London Heathrow Airport to Belfast International Airport, Northern Ireland, having already flown from Heathrow to Belfast and back that day. The plane was new, having accumulated 521 airframe hours since it first went into service in 1988.
Captain Kevin Hunt (43) and First Officer David McClelland (39). Captain Hunt was a veteran British Midland pilot who had been with the airline since 1966 and had approximately 13,200 hours of flying experience. First Officer McClelland joined British Midland in 1988 and had accrued roughly 3,300 total flight hours. Between them, the pilots had close to 1,000 hours in the Boeing 737 cockpit; only 76 of which were logged in Boeing 737-400 series aircraft.
After taking off from Heathrow at 7:52 p.m., Flight BD 092 was climbing through 28,300 feet to reach its cruising altitude of 35,000 feet when a blade detached from the fan of the port (left) CFM International CFM56 engine. While the pilots did not know the source of the problem, a pounding noise was suddenly heard, accompanied by severe vibrations. In addition, smoke poured into the cabin through the ventilation system and a burning smell entered the plane.(p1) Several passengers sitting near the rear of the plane noticed smoke and sparks coming from the left engine.
After the initial blade fracture, Captain Kevin Hunt had disengaged the plane's autopilot.(p3) When Hunt asked First Officer David McClelland which engine was malfunctioning, McClelland replied: "It's the le— ... no, the right one".(p3) In previous versions of the 737, the left air conditioning pack, fed with compressor bleed air from the left (number 1) engine, supplied air to the flight deck, while the right air conditioning pack, fed from the right (number 2) engine supplied air to the cabin. On the 737-400 this division of air is blurred; the left pack feeds the flight deck but also feeds the aft cabin zone, while the right feeds the forward cabin. The pilots had been used to the older version of the aircraft and did not realise that this aircraft (which had only been flown by British Midland for 520 hours over a two-month period) was different. The captain later claimed that his perception of smoke as coming forward from the cabin led them to assume the fault was in the right engine.(p98) The pilots throttled back the working right engine instead of the malfunctioning left engine.(p98) They had no way of visually checking the engines from the cockpit, and the cabin crew — who did not hear the commander refer to the right hand engine in his cabin address — did not inform them that smoke and flames had been seen from the left engine.(p5)
When the pilots completely shut down the right engine, they could no longer smell the smoke, which led them to believe that they had correctly dealt with the problem. As it turned out, this was a coincidence: when the autothrottle was disengaged to shut down the right engine, the fuel flow to the left engine was reduced, and the excess fuel which had been igniting in the jet exhaust disappeared; therefore, the ongoing damage was reduced, the smoke smell ceased, and the vibration reduced, although it would still have been visible on cockpit instruments.(p99)
During the final approach to the East Midlands Airport, more fuel was pumped into the damaged engine to maintain speed, which caused it to cease operating entirely and burst into flames. The flight crew attempted to restart the right engine by windmilling, using the air flowing through the engine to rotate the turbine blades and start the engine, but the aircraft was by now flying at 185 km/h (115 mph), too slow for this. Just before crossing the M1 motorway, the tail struck the ground and the aircraft bounced back into the air and over the motorway, knocking down trees and a lamp post before crashing on the far embankment and breaking into three sections approximately 475 metres (519 yd) short of the active runway's paved surface and approximately 630 metres (689 yd) from its threshold.(pp6-7) Remarkably, there were no vehicles on that part of the motorway at the moment of the crash.
Of the 118 passengers on board, 39 were killed outright in the crash and eight died later of their injuries, for a total of 47 fatalities. All eight members of the crew survived the accident. Of the 79 survivors, 74 suffered serious injuries and five suffered minor injuries. In addition, five firefighters also suffered minor injuries during the rescue operation.(p7) No one on the motorway was injured, and all vehicles in the vicinity of the disaster were undamaged. The first person to arrive at the scene to render aid was a motorist, Graham Pearson. A former Royal Marine, he helped passengers for over three hours and subsequently received damages for post-traumatic stress disorder.
Shutting down the wrong engine
Captain Kevin Hunt believed the right engine was malfunctioning due to the smell of smoke in the cabin because in previous Boeing 737 variants bleed air for cabin air conditioning was taken from the right engine. Starting with the Boeing 737-400 variant, Boeing had redesigned the system to use bleed air from both engines. Several cabin staff and passengers noticed that the left engine had a stream of unburnt fuel igniting in the jet exhaust, but this information was not passed to the pilots because cabin staff assumed they were aware that the left engine was malfunctioning.(pp106)
The smell of smoke disappeared when the autothrottle was disengaged and the right engine shut down due to reduction of fuel to the damaged left engine as it reverted to manual throttle.(p99) In the event of a malfunction, pilots were trained to check all meters and review all decisions, and Captain Hunt proceeded to do so. Whilst he was conducting the review, however, he was interrupted by a transmission from East Midlands Airport informing him he could descend further to 12,000 feet (3,700 m) in preparation for the diverted landing. He did not resume the review after the transmission ended, and instead commenced descent. The vibration indicators were smaller than on the previous versions of the 737 in which the pilots had the majority of their experience.(p69)
The dials on the two vibration gauges (one for each engine) were small and the LED needle went around the outside of the dial as opposed to the inside of the dial as in the previous 737 series aircraft. The pilots had received no simulator training on the new model, as no simulator for the 737-400 existed in the UK at that time. At the time, vibration indicators were known for being unreliable(pp69-70) (and normally ignored by pilots), but unknown to the pilots, this was one of the first aircraft to have a very accurate vibration readout.
Analysis of the engine from the crash determined that the fan blades (LP Stage 1 compressor) of the uprated CFM International CFM56 engine used on the 737-400 were subject to abnormal amounts of vibration when operating at high power settings above 10,000 feet (3,000 m).(pp118-120) As it was an upgrade to an existing engine, in-flight testing was not mandatory, and the engine had only been tested in the laboratory. Upon this discovery the remaining 99 Boeing 737-400s then in service were grounded and the engines modified. Following the crash, it is now mandatory to test all newly designed and significantly redesigned turbofan engines under representative flight conditions.
This unnoticed vibration created excessive metal fatigue in the fan blades, and on G-OBME this caused one of the fan blades to break off. This damaged the engine terminally and also upset its delicate balance, causing a reduction in power and an increase in vibration. The autothrottle attempted to compensate for this by increasing the fuel flow to the engine. The damaged engine was unable to burn all the additional fuel, with much of it igniting in the exhaust flow, creating a large trail of flame behind the engine.
The official report into the disaster made 31 safety recommendations.
Evaluation of the injuries sustained led to considerable improvements in aircraft safety and emergency instructions for passengers. These were derived from a research programme funded by the CAA and carried out by teams from the University of Nottingham and Hawtal Whiting Structures (a consultancy company). The study between medical staff and engineers used analytical "occupant kinematics" techniques to assess the effectiveness of the brace position. A new notice to operators revising the brace position was issued in October 1993.
There is a memorial to "those who died, those who were injured and those who took part in the rescue operation", in the village cemetery in nearby Kegworth, together with a garden made using soil from the crash site.
Hunt suffered injuries to his spine and legs in the crash. In April 1991 he told a BBC documentary: "We were the easy option—the cheap option if you wish. We made a mistake — we both made mistakes — but the question we would like answered is why we made those mistakes." BM later paid McClelland an out-of-court settlement for unfair dismissal.
Graham Pearson, a man who assisted Kegworth survivors, sued the airline and was awarded £57,000 in damages in 1998.
British Midland Flight BD 092 was featured in an episode of Seconds From Disaster, called "Motorway Plane Crash".
Most recently it was featured in a Season 14 episode of television series Mayday (Air Crash Investigation in some countries). The episode featuring British Midland Flight 92 is titled "M1 Plane Crash," or, in some locales, "Choosing Sides."
- List of accidents and incidents involving commercial aircraft
- TransAsia Airways Flight 235, another incident when the pilot shut off the wrong engine
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- Macarthur Job, Air Disaster Volume 2: Aerospace Publications Pty Ltd, 1996, ISBN 1-875671-19-6, p. 173–185
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- HW Structures, CAA Paper 90012 Occupant modelling in aircraft crash conditions: Civil Aviation Authority, 1990, ISBN 0-86039-445-X.
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- BBC 10th anniversary page about the crash
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- Pre-crash and crash pictures of the aircraft from Airliners.net