The British accident report does a good job of dissecting the events that led to this crash, but they miss the actual cause.
The aircraft experienced a compressor stall that did not immediately cause the left engine to fail, but did cause severe vibration and smoke through the air conditioning system. The captain's experience in previous aircraft told him the smoke had to be coming from the right engine and he very quickly disconnected the autothrottles and brought the right engine back to idle. The compressor stalls eased, leading both pilots to believe they got the correct engine. Neither discerned from the engine instruments the real problem and because the right engine was at idle, they were denied a chance to compare the two engines. The captain had several opportunities to discern the real situation from the airplane's yaw before and after retarding the right engine to idle. They shut down the wrong engine and when the left engine finally quit, they had no place to go but down.
The accident report gets all that. But why did both pilots react so quickly to a situation that called for a more deliberate approach? I think they panicked. Both pilots wanted to resolve the situation quickly and fooled themselves along the way that the problem was resolved. There are very few situations in a modern airplane where actions need to be immediate. More about this: Panic.
Everything here is from the references shown below, with a few comments in an alternate color.
Photo: Crash site of G-OBME, from Accident Report, figure 1.
[Accident Report, ¶1.1]
The commander was basing his idea that air conditioning smoke comes from the right engine from a previous aircraft he had flown. The correlation does not exist in this aircraft. The speed at which both pilots reacted was contrary to their training and robbed them of time they could have better spent studying the engine instruments.
Had the commander kept the aircraft in coordinated flight prior to throttling back the right engine, he would have another clue that the left engine was producing less thrust than the right, because he would have needed right aileron to level the wings followed by right rudder to eliminate the yaw and return the ailerons to neutral.
Here again was another clue. If the No 2 engine was at idle and there was no adverse yaw, the No 1 engine could not have been producing much thrust.
Even had their diagnosis of which engine was causing the vibration and smoke in the cabin been correct, there was no need to shut the engine down and the smoke could have been addressed by closing bleed switches or even shutting down the air conditioning system completely once they had descended to a lower altitude.
The commander may have preferred to fly the airplane manually because it was a familiar activity and provided a comfort. Using the autopilot, however, would have freed his attention span to take over some of the first officer's duties.
They could have done this a few minutes earlier, but at this point they were outside the engine's relight envelope.
[Accident Report, ¶2.1] After an uneventful takeoff and climb the crew suddenly heard an unusual noise, accompanied by vibration, as the aircraft passed through FL283. The noise was heard in the cabin as a series of thuds and the FDR indicated that it was directly associated with the stalling of the fan and/or LP compressor with attendant surging of the No 1 engine. In addition to the noise and vibration, the lateral and longitudinal accelerations recorded on the FDR were consistent with the reported lower frequency shuddering that was sufficiently marked to shake the walls of the forward galley. Very soon after the onset of these symptoms there was a smell of fire and possibly some visible smoke in the cockpit. The combination was interpreted by the pilots as evidence of a serious engine malfunction, with an associated fire, and appears to have driven them to act very quickly to contain this perceived condition.
[Accident Report, ¶3.(a) 19] The No 1 engine suffered fatigue of one of its fan blades which caused detachment of the blade outer panel. This led to a series of compressor stalls, over a period of 22 seconds until the engine autothrottle was disengaged.
[Accident Report, ¶3.(a) 3] The flight deck crew experienced moderate to severe engine induced vibration and shuddering, accompanied by smoke and/or smell of fire, as the aircraft climbed through FL283. This combination of symptoms was outside their training or experience and they responded urgently by disengaging the autothrottles and throttling-back the No 2 engine, which was running satisfactorily.
[Accident Report, ¶2.1] Neither pilot appears to have assimilated from the engine instruments any positive indication of malfunction, but subsequent tests show the engine instrument system to have been serviceable and there was no evidence to indicate that it did not display the large engine parameter variations that occurred when the compressor surged. The FDR showed four distinct excursions in N1 on the No 1 engine, with a 6 second period of relative stability between the second and third.
[Accident Report, ¶3.(a) 4] After the autothrottle was disengaged, and whilst the No 2 engine was running down, the No 1 engine recovered from the compressor stalls and began to settle at a slightly lower fan speed. This reduced fan speed after the autothrottle was disengaged, and whilst the No 2 engine was running down, the No 1 engine recovered from the compressor stalls and began to settle at a slightly lower fan speed. This reduced the shuddering apparent on the flight deck, convincing the commander they had correctly identified the No 2 engine as the source of the problem.
[Accident Report, ¶2.1]
[Accident Report, ¶3.(a) 24] Fifty three seconds before ground impact, the No 1 engine abruptly lost thrust as a result of extensive secondary fan damage.
[Accident Report, ¶3 (b)] The cause of the accident was that the operating crew shut down the No 2 engine after a fan blade had fractured in the No 1 engine. this engine subsequently suffered a major thrust loss due to secondary fan damage after power had been increase during final approach to land. The following factors contributed to the incorrect response of the flight crew:
Aircraft Accident Report 4/90, Department of Transport, Air Accidents Investigation Branch, Royal Aerospace Establishment, Report on the accident to Boeing 737-400 G-OBME near Kegworth, Leicestershire on 8 January 1989
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