Air France’s Airbus A380 uncontained engine failure during the flight AF066 in September 2017 resulted from the lack of scientific understanding about the alloy used for the engine parts, the Bureau of Enquiry and Analysis for Civil Aviation Safety (BEA) said in a full report on September 25, 2020.
Air France Airbus A380 engine explosion
On September 30, 2017, the Airbus A380 (registered F-HPJE) flight AF066 was en route from Paris Charles de Gaulle Airport (CDG) to Los Angeles International Airport (LAX). The aircraft was carrying 497 passengers and 24 crew members when its engine No. 4 failed with an explosion five hours into the flight over southern Greenland.
A visual examination found that the first rotating fan assembly at the front of an engine and the air inlet and fan case had separated mid-flight and caused minor structural damage to the aircraft. The A380 landed two hours later at the Canadian Forces Base Goose Bay (YYR) without any injuries or further events.
The wasteland search for the Airbus A380 engine parts
After the incident, the BEA conducted a three-phase search operation to gather the scattered engine parts. It took several visual scanning and aerial radar campaigns to detect the parts using synthetic aperture radars (SAR) and ground-penetrating radars (GPR) before finally retrieving the pieces.
Overall, it took the researchers 21 months to collect the missing parts before conducting the final analysis.
The A380 engine flaw science was not aware of
The GP7200 engine was built by Engine Alliance, a consortium of General Electric and Pratt & Whitney, using titanium alloy Ti-6-4.
The analysis released by the French authority on September 25, 2020, clearly emphasized that the incident was no fault of the engine manufacturer or Airbus. At the time, the scientific community was not aware of Ti-6-4 titanium alloy’s susceptibility to cold dwell fatigue.
Metal alloys that are used for aircraft engines are often expected to operate at over 300˚C (572˚F), according to the Federal Aviation Administration (FAA). However, if the motor performs at a lower temperature than that, it becomes susceptible to ‘cold’ dwell fatigue, significantly reducing the expected engine cycles to failure. In the case of Air France A380, the engine failed after 3,544 flight cycles when the estimated minimum life of the titanium part was 15,000 cycles.
Scientists have known about the cold dwell fatigue phenomenon in other titanium alloys like IMI 685 or Ti-6242 for about 40 years. Nevertheless, the “Ti-6-4 was not considered sensitive to cold dwell fatigue (…) up until the failure of the (GP7270) engine No 4 fan hub,” the BEA report said.
The analysis concluded that both the European Union Aviation Safety Authority (EASA) and the Federal Aviation Administration (FAA) should ensure that the design, sizing, and manufacturing criteria for Ti-6-4 alloy engine parts are revised. BEA also recommended both authorities to adopt a new in-service inspection program to detect possible indications of cold dwell fatigue in the same alloy engines.