What happened
During the initial climb-out from Runway 23 at Toronto-Lester B. Pearson International Airport, an Air Canada Boeing 777-333ER (registration C-FITW) experienced a failure of its number 2 engine. The aircraft, carrying 309 passengers and 16 crew members, was departing for Tokyo, Japan, when the engine lost power at approximately 1,590 feet above ground level.
Following the failure, the flight crew observed rapid decreases in fan speed, compressor speed, and oil pressure, alongside a significant spike in exhaust gas temperature. The crew executed the engine severe damage checklist, secured the engine, and declared an emergency. To reach a safe landing weight, the crew jettisoned 86,600 kg of fuel. The aircraft returned to Toronto for an uneventful landing. While there were no injuries to anyone on board, debris ejected from the engine exhaust caused minor damage to the underside of the aircraft's right wing and struck several vehicles on the ground.
The investigation
The investigation focused on the mechanical cause of the engine failure. Preliminary examinations of the engine revealed that the propulsor core had seized due to fragments from the high-pressure turbine (HPT) stage 2 nozzle being jammed in the machinery. Investigators found pooled oil and hardware fragments in the engine exhaust cone, with damage consistent with extreme heat and debris impact.
Technical analysis of the engine's maintenance history showed that the engine was subject to a specific GE service bulletin regarding high-pressure turbine stage 1 shroud control. The investigation examined the manufacturing process of the shrouds, specifically noting that a high-intensity laser used during production had altered the shape of the cooling holes.
Findings
- A change in the laser intensity used during the production of the shrouds created variations in the size and shape of the cooling holes.
- Over time, these irregular holes eroded, leading to degraded cooling and the creation of a super-heated zone within the engine.
- The failure of the high-pressure turbine stage 1 shroud caused the number 2 engine to shut down during takeoff.
- Damage to the shrouds and hangers was likely present during the previous borescope inspection but went undetected, allowing the engine to remain in service.