What happened
On September 5, 2017, a Japan Airlines Boeing 777-300ER, registered JA7SB, was performing a scheduled takeoff from runway 34R at Tokyo International Airport, bound for New York. Seconds after lift-off, the aircraft's No. 1 (left) engine experienced a sudden drop in RPM and an engine failure indication. The flight crew observed a flame trailing from the engine, and air traffic controllers witnessed a visible flame behind the engine nacelle.
Following the engine failure, the crew initiated an emergency return to the airport. To manage the aircraft's weight for landing, the crew performed a fuel dump over the coast of Tateyama City. The aircraft landed safely on runway 34L with no injuries to the 251 people on board. However, the incident left debris scattered across the runway and caused a small fire in the grass area adjacent to the takeoff site due to high-temperature fragments exiting the engine.
The investigation
The JTSB investigation focused on the structural integrity of the GE90-115B engine. Investigators examined the low pressure turbine (LPT) and discovered that multiple stages of stator vanes and turbine blades had sustained significant damage. Notably, a hole measuring approximately 6 cm by 1 cm had been punched through the turbine rear frame (TRF).
Technical analysis by the National Institute for Materials Science (NIMS) and the engine manufacturer examined the fractured components. Using scanning electron microscopy, investigators identified fatigue striations on a fractured fifth-stage stator vane. The investigation also looked into the phenomenon of "arch-binding," where adjacent engine segments become stuck together, increasing mechanical stress.
Findings
The investigation established that the primary cause of the incident was the collision of engine fragments with the turbine rear frame, which created a hole in the structural component. This sequence was triggered by the initial fracture of a single fifth-stage LPT stator vane.
Contributing factors included:
- The fracture of the fifth-stage stator vane was driven by a crack that originated at the trailing edge and progressed toward the leading edge.
- This cracking process was caused by stress concentration resulting from arch-binding, where the inner platforms of adjacent stator vane segments rubbed together, creating wear and impeding free movement.
- The repetitive stress of normal engine operations allowed the fatigue crack to eventually lead to the complete fracture of the vane, subsequently causing the downstream destruction of multiple turbine blades and vanes.