What happened
On 12 March 1998, a Boeing 777-20 and registration G-VIIH was prepared for a scheduled passenger flight from London Heathrow to Boston. During the takeoff roll, after the crew had set takeoff power, a loud bang occurred, causing the aircraft to veer to the left. The crew immediately initiated an emergency stop, with the commander closing the thrust levers and the first officer selecting reverse idle.
Following the deceleration, an engine failure warning was triggered for the left-hand engine. The crew followed established emergency procedures, including notifying the fire service and assigning cabin crew to monitor the engine for fire. After consulting with airport fire services and air traffic control, the crew decided to start the APU and taxi the aircraft away from the runway using the remaining engine. The aircraft was eventually moved to a stand, where the 230 passengers and 15 crew members were safely disembarked without any injuries or fatalities.
The investigation
Investigators examined the left-hand GE90-85B engine and found that turbine debris had been ejected through the tailpipe onto the runway, though the engine containment remained intact. Flight data recorder analysis showed that at an airspeed of 71 kt, there was a sudden drop in N1 on the number 1 engine.
Technical inspections via borescope revealed that while the high-pressure turbine was undamaged, the low-pressure turbine (LPT) was seized and had sustained extensive damage. Specifically, investigators found that at least one segment of the nozzle guide vanes had migrated aft into the plane of the LPT stage 1 blades. This displacement caused a cascade of damage through the subsequent LPT stages.
Findings
- The engine failure was caused by the misassembly of the nozzle guide vane segments, which allowed them to move aft and interfere with the LPT stage 1 blades.
- The investigation confirmed that the geometry of the mating flanges meant the segments could only have become displaced through improper installation during assembly.
- This specific engine was exempt from a previously recommended borescope inspection because it had been manufactured at a facility using a different assembly technique than those covered by the initial recommendation.