MIAMI – This morning, the BEA released the final report into the uncontained failure of Engine four of Air France (AF) flight AF066. The engine failure had occurred over Greenland; however, the Accident Investigation Board Denmark delegated the investigation to the BEA.
This article is based on the English version of the final report from the BEA, the French Land Transport Accident Investigation Bureau. Flight 066 was scheduled on September 30, 2017, from Paris to Los Angeles. The aircraft, F-HPJE, was equipped with Engine Alliance GP7270 engines.
The flight was normal until the aircraft was over Greenland. After the engine failure, the aircraft declared an emergency and diverted to Goose Bay Airport (YYR) in Canada.
The engine failure caused most of the fan, the engine cowlings and most structure on the front of the engine to separate. The debris did impact the wing with no major damage, and none entered the cabin.
Engine four had the highest total operating times and cycles of all four engines. It also had the highest operating time since the last inspection.
As the failure occurred over Greenland, high priority was placed on recovering the fan hub. Using ballistic calculations, the investigation team was able to narrow down the search area. In the summer of 2019, the BEA was able to recover the fan hub for analysis.
The fan hub failed due to cold dwell fatigue, starting in a macro-zone area. A macro-zone is an area in the titanium alloy where all the grains are the same, and they occur when the metal is cooled. Unfortunately, there is currently no non-destructive method of measuring these zones, and it so happens that the one in this fan hub was considerably larger than those in the test piece.
At the time of certification, cold dwell fatigue was not known to affect this specific alloy, therefore it was not considered to be a hazard. As this is no longer the case, there is research occurring to determine the exact effects of this type of fatigue and to see how engineers can design against it.
Featured image: Air France Airbus A380. Photo: Airbus