What happened
On December 13, 2013, an All Nippon Airways Boeing 777-200, registration JA701A, was climbing through approximately 32,600 feet toward Fukuoka when the crew detected a malfunction in the No. 2 engine. Flight instruments indicated a drop in thrust accompanied by a rise in exhaust gas temperature (EGT).
In response to the engine instability, the crew shut down the right engine. The aircraft subsequently performed an emergency descent and returned to Tokyo International Airport, landing safely at 09:15 JST. There were no injuries during the incident.
The investigation
The Japan Transport Safety Board (JTSB) conducted an investigation into the internal damage sustained by the Pratt & Whitney PW4074 engine. Investigators examined the compressor components, specifically focusing on the Low Pressure Compressor (LPC) and High Pressure Compressor (HPC).
Findings revealed extensive destruction within the engine's core. While the fan and the initial stages of the LPC remained intact, the sixth stage of the LPC showed trailing edge damage, including nicks and tears. The most significant destruction was located in the HPC. The first-stage blades of the HPC were found to be either fractured at the airfoil roots or entirely missing from their slots. Additionally, the second-stage blades of the HPC had also fractured at their roots, causing secondary damage to the downstream engine structure.
Upon inspecting the first-stage disk, investigators noted that 16 blades had completely detached from their slots. In several instances, the blade lock fittings were missing. One specific slot exhibited abnormal damage on the reverse flank, which differed from the scratch marks found in the other slots.
Findings
Analysis of the engine components suggests that the internal damage was triggered by a failure in the first-stage HPC blades. The investigation concluded that it is highly probable that one blade sustained damage at its dovetail part and detached from its slot, initiating a chain reaction. This initial failure caused the blades around the entire periphery of the first-stage disk to fail, leading to the widespread internal destruction observed.