SHUTTING DOWN THE ‘GOOD’ (WRONG) ENGINE

BRITISH MIDLANDS FLIGHT 092: 08 JAN 1989: BOEING 737 – 400

SYNOPSIS

Flight 092 left London for Belfast at 19:52h with a crew of 8, and 118 passengers on board. While climbing through FL283 moderate to severe vibration that was accompanied by ingress of smoke and fumes in to the flight deck were felt, as also fluctuations in the engine parameters of the No. 1 engine. Investigations revealed that these were the result of one of the outer panel of one of the no. 1 engine fan blades getting detached in flight, causing a series of compressor stalls that lead to airframe shuddering.

Believing the No. 2 engine had suffered damage, the crew throttled it back. The shuddering stopped, leading the flight crew to believe that their actions were correct, and they thus shut down the No 2 engine. The No. 1 engine operated normally after the initial severe vibrations, and during the descent in to East Midlands, the diversionary airfield.

The flight was cleared for an approach on to runway 27. The instrument approach on No. 1 engine continued normally, although with a high level of vibrations from the live engine. At 900 feet, 2.4nm from the runway, no. 1 engine suddenly suffered a reduction in power followed by a fire warning on this engine. Attempts to restart No. 2 engine were not successful. As the speed fell below 125 knots, the stick shaker activated and the aircraft struck trees at a speed of 115 knots. The aircraft continued and impacted the western carriageway of the M1 motorway 10 m lower and came to rest against the wooded embankment, 900 m short of the runway.

39 passengers died in the accident, and 8 more died later due to the injuries sustained. Of the remaining 79 occupants, 74 suffered serious injuries.

(Image Courtesy: Google Images: Aerial view of Crash site)

PROBABLE CAUSE

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 increased during the final approach to land.

The following factors contributed to the incorrect response of the flight crew

1. The combination of heavy engine vibration, noise, shuddering and an associated smell of fire were outside their training and experience.

2. They reacted to the initial engine problem prematurely and in a way that was contrary to their training. (Either pilot does not remember having noticed the engine parameters like N1, EGT, N2 or Oil Pressures of the engines before throttling back No. 2 engine).

3. They did not assimilate the indications on the engine instrument display before they throttled back the No. 2 engine. (The crew’s familiarity of the newly introduced EIS on the B 737-400 variant could have been a factor. The Captain had 23 hours and the first officer had 53 hours on the B 737-400. Both were given a 1day training session on the EIS, as there was no flight simulator available with the EIS. The variants before the B737-400 had the normal electro-mechanical engine instruments).

4. As the No 2 engine was throttled back, the noise and shuddering associated with the surging of the No 1 engine ceased, persuading them that they had correctly identified the defective engine. (The Auto Throttle system was disengaged while bringing No. 2 engine throttle back to idling. This led to manual control of the engines, and No. 1 engine fuel flow settled as per the prevailing engine conditions, rather than as demanded by the auto throttle to maintain flight parameters).

5. They were not informed of the flames which had emanated from the No.1 engine and which had been observed by many on board, including 3 cabin attendants in the aft cabin. (Inadequate communications between flight and cabin crew – a CRM issue that is greatly emphasised now).