What happened
On December 6, 2010, at approximately 11:15 UTC, a TAAG - Linhas Aéreas de Angola flight, operating a Boeing 777-200 with registration D2-TEF, experienced an engine malfunction shortly after departing Lisbon Airport. After taking off from runway 21 and climbing through 5,000 feet, the number 2 (right-hand) engine experienced a loss of N1 rotation, accompanied by an increase in Exhaust Gas Temperature (EGT) and significant engine vibration. The crew responded by reducing the power lever, which mitigated the vibration, and stabilized the aircraft at 5,000 feet to perform necessary checklists. The flight was subsequently diverted back to Lisbon, and the crew performed a single-engine landing at approximately 11:32 UTC.
The investigation
The GPIAAF investigation focused on several key areas, including flight operations, crew performance, and engine condition monitoring. Investigators examined the aircraft's flight data recorder (SSFDR) and cockpit voice recorder (CVR), both of which were found to be in good working order. A physical inspection of the GE 90 engine revealed substantial damage to the low-pressure turbine (LPT) stages. Specifically, investigators found that the LPT stage 1 nozzle was missing parts and the inlet guide vanes were severed near the root. Borescopic inspections indicated that while the high-pressure turbine (HPT) and compressor appeared to be in good condition, the LPT showed evidence of material failure likely caused by excessive temperatures. Additionally, the investigation noted that the crew of the preceding flight had reported unusual EGT values, and GE was monitoring similar incidents in other fleets involving potential fuel injector malfunctions.
Findings
- The primary cause of the engine damage is suspected to be malfunctioning fuel injectors, which likely caused localized overheating in the turbine section.
- The excessive temperatures led to the failure and separation of the LPT stage 1 nozzle and vanes, which subsequently caused progressive damage to the downstream LPT components.
- There was no evidence of foreign object ingestion (FOD) at the engine intake or bypass ducts.
- Meteorological conditions were not a contributing factor to the engine failure.
- The crew was fully qualified, and all required licenses and medical certificates were valid.
- The aircraft was maintained in accordance with its approved maintenance program.