History of Flight
The aircraft, a Boeing 777-200 registered G-VIIH, was scheduled for a passenger flight from London Heathrow to Boston, USA. The engines were started at 1854 UTC with no reported defects. Light rain was falling, and the crew selected engine anti-ice to 'On'. After taxiing to the holding point for Runway 27L, the aircraft was cleared to line up at 1900 UTC. The rain had stopped, but the commander decided to keep the anti-ice system active due to possible cloud after takeoff. During the takeoff roll, with engines set to the assumed temperature of +44°C (derated power), a loud bang occurred shortly after the first officer called "Power Set." The aircraft veered left. Both pilots called "Stop," and the commander closed the thrust levers while the first officer selected reverse idle. The "Engine Fail" aural warning sounded, and the master caution light illuminated. After stopping on the runway, the commander performed the engine fail drill for the left engine and requested fire services. Following discussions, the APU was started, and the aircraft taxied to the stand using only the right engine. Passengers disembarked normally. Initial examination revealed turbine debris in the tailpipe and on the runway, but no containment failure or secondary damage.
Flight Recorder Data
The aircraft was equipped with a solid-state cockpit voice recorder and a Sundstrand solid-state flight data recorder, along with an optical quick access recorder. Data analysis showed normal acceleration until 71 knots indicated airspeed, at which point there was a sudden decrease in N1 on the left engine from 93% to lower values, while N2 remained at 106.5%. The throttles were retarded one second later, and the maximum exhaust gas temperature on the left engine reached 965.5°C. The maximum recorded airspeed was 75 knots.
Technical Examination
The left engine was a General Electric GE90-85BG04, serial number 900158, which had been installed since aircraft delivery. It had accumulated 3,166 hours and 511 cycles with no significant defects noted in maintenance records. Borescope inspection revealed that the high-pressure turbine rotated freely and appeared undamaged, while the low-pressure turbine (LPT) was seized with extensive damage from stage 1 aft. At least one segment of nozzle guide vanes had migrated aft into the plane of the LPT stage 1 blades, causing damage that cascaded rearward through subsequent stages. The damage pattern was similar to a 1997 incident involving another GE90-85B engine (serial number 900114) that failed on a testbed due to misassembly. In that earlier case, a vane segment had not been properly engaged during LPT module fitting. As a result, a borescope inspection had been recommended for new, rebuilt, and low-time engines, but engines built at the manufacturer's Durham, NC facility were exempted because of differences in assembly techniques. Engine 900158 was from the Durham facility and therefore not inspected. Disassembly at the manufacturer's facility confirmed that two vane segments around the 12 o'clock position had been displaced aft due to misassembly, supported by lack of witness marks at the flanges. The segments interfered with stage 1 LPT blades, causing the failure. Unlike the earlier incident, which occurred after only four hours, this engine operated for 3,166 hours before failure, possibly because the two segments locked together temporarily.
Subsequent Actions
Following the G-VIIH incident, the engine manufacturer issued Alert Service Bulletin ASB 72-A405 on 28 March 1998, requiring borescope inspection of all in-service engines. The fleet inspection was completed by the end of March with no further instances of displaced vane segments. The manufacturer also incorporated the inspection into production and overhaul procedures and began evaluating design and tooling changes to reduce the likelihood of such misassembly.