Summary of Aircraft Accidents and Serious Incidents, and Measures
A summary of past safety troubles and measures
FY2017
Aircraft Accident
Fatal or serious injury of an person as a result of the operation of an aircraft, or an aircraft crash, collision or fire, as classified by the Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT).
There was no aircraft accident in FY2017
Serious Incident
An incident involving circumstances indicating that there was a high probability of an accident, such as overrunning, emergency evacuation, fire or smoke inside the cabin and abnormal depressurization, encountering abnormal weather conditions, etc, as classified by the Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT).
Return to origin after take-off of JAL flight 006 case.
Outline
On September 5, JAL Flight 006 (Tokyo, Haneda - New York.JFK) experienced left engine trouble during take-off from runway 34R. Flight crew shut down the engine and declared emergency situation to Air Traffic Controller then turned back to Haneda airport.
After an engine inspection revealed that several parts of the rear body of the engine including low pressure turbines were damaged. Consequently, the case was classified today as a Serious Incident by Japan Civil Aviation Bureau, Ministry of Land, Infrastructure, Transport and Tourism (MLIT).
Investigation into the cause
Investigations were conducted by the Japan Transport Safety Board, and the Serious incident investigation report was disclosed on October 31, 2019. It suggests that, several stages of vane and rotor in the low pressure turbine (LPT) of No.1(left) engine were damaged soon after taking off, and some of those fragments hit the turbine rear frame (TRF) and made a hole.
As for several stages of vane and rotor in the LPT were damaged, it is presumed that the damage was caused by a fracture of one vane in the 5th stage of LPT.
As for fracture of one vane in the 5th stage of LPT, it is presumed that the vane was fractured because a crack caused by stress concentration with arch-binding* proceeded by repetitive stress accompanied by engine operation.
(*) Condition that each adjacent vane segments contact tightly and are restrained.
Each engine structure grows according to the thermal effect during operation. When vane segment grows faster than surrounding structures, gaps which absorb the segment grow will go away and each adjacent vane segments contact tightly. As a result, stress concentration will occur on the vane.
Countermeasures
JAL implemented the following measures after this incident.
- Emergency inspections for all 777-300ER engines were performed in order to confirm if vanes in the 5th stage of LPT would be healthy, and found no damage. Further, JAL is doing repetitive inspection every 250 flight cycles after that.
- Maker has published the service bulletin instructing to make more gaps between vane segments in order to prevent contact which causes fracture of vane in the 5th stage of LPT. (August, 2019) JAL will apply the modification for 777-300ER engines according to the service bulletin and will begin on the engine removed this November.
