What happened
On May 24, 2018, a Japan Airlines Boeing 767-300, registered JA8980, was climbing through approximately 7,500 feet near Kumamoto Airport when the crew experienced intense vibrations and abnormal noise from the No. 1 engine. Flight data indicated a drop in engine RPM alongside a sharp increase in exhaust gas temperature and vibration levels. The crew responded by reducing engine thrust to idle and, after attempting to follow non-normal checklists, decided to return to the airport. The aircraft landed safely, but a post-flight inspection revealed severe internal damage to the engine.
During the event, fragments from the engine were ejected through the exhaust nozzle. These pieces struck the ground near the flight path, causing damage to the roofs and windows of buildings as well as the windshield of a vehicle on the ground. No injuries were reported among the 217 people on board.
The investigation
Investigators from the JTSB examined the engine's high-pressure and low-pressure turbine components. The inspection found that the second stage of the high-pressure turbine (HPT) had suffered multiple blade fractures. Specifically, one blade (number 13) had broken at the shank, while others were fractured at the airfoil or tips. This damage triggered a chain reaction, causing subsequent damage to the low-pressure turbine (LPT) and creating a 9 cm long hole in the LPT casing.
Metallurgical analysis of the fractured HPT blade revealed that the failure originated from the cooling air passage area. The investigation identified evidence of low-cycle fatigue and hot corrosion (blistering) on the blade surface. Furthermore, the aluminide coating on certain blades was found to be thicker than others, which may have increased the risk of cracks forming in the coating and progressing into the base metal.
Findings
- The primary cause of the incident was the fracture of HPT stage 2 blade #13, which initiated a sequence of damage through the turbine stages.
- This fracture led to the destruction of subsequent blades and stator vanes, eventually causing fragments to strike the LPT casing and create a breach.
- The failure was driven by cracks originating in the cooling air passage area, likely exacerbated by low-cycle fatigue and hot corrosion.
- A thicker aluminide coating on certain blades may have reduced ductility, making the material more susceptible to cracking at lower temperatures.
Safety action
Following the incident, the Japan Civil Aviation Bureau instructed domestic operators of similar engines to perform immediate borescope inspections of the HPT stages. Japan Airlines proactively replaced 258 blades of the problematic type across its fleet with newer, more resistant versions. The engine manufacturer was also tasked with monitoring component service cycles and providing updated maintenance information to prevent similar occurrences.