What happened
On January 4, 2009, at 18:01 UTC, an Air France Boeing 777-300ER, registration F-GSQN, was operating a passenger flight from Paris Orly to Fort de France. While flying over the Atlantic Ocean, the aircraft experienced an uncommanded spool down of the fan and core rotors on the number one engine, triggering a "caution ENG FAIL L" message. The flight crew subsequently performed an in-flight shutdown of the engine. The aircraft, carrying 475 passengers and 15 crew members, diverted from its original route and landed safely at Lajes Air Base (LPLA) in the Azores at 20:00 UTC.
The investigation
The GPIAAF investigation established that the failure occurred while the aircraft was approximately 600 nautical miles from Lajes Air Base. A maintenance team from Air France traveled to Lajes Air Base to inspect the affected GE90-115B engine. Their inspection identified a failure within the transfer gearbox (TGB) as the cause of the shutdown. Additionally, the flight data recorder was removed and sent to France for data extraction.
Findings
Ground inspections revealed that the cause of the in-flight engine shutdown was the failure of the transfer gearbox (TGB) horizontal bevel gearshaft. The engine had accumulated 8,105 flight hours and 1,064 cycles since new. The investigation noted that the TGB involved in the event featured the original configuration gear, which lacked several recent improvements, including a shot-peened damper ring groove, a silver-plated damper ring, and the removal of fretted ring groove surface material via rework. This specific type of gear separation had been observed in previous incidents.
Safety action
Following the event, the engine manufacturer, GE, issued a notice to all operators of the GE90-115B engine. GE recommended that operators continue performing the on-wing ultrasonic inspection program in accordance with SB 72-0263 and proceed with the retrofit program for increased web thickness gear shafts as per SB 72-0272.