AF66 / 30-sep-2017

A three-year French investigation into a near-catastrophic Airbus SE A380 engine blowout over Greenland found hidden weaknesses in the structure of a widely used metal alloy, with safety implications for plane equipment worldwide.

Microscopic cracks beneath the surface of a titanium alloy caused one engine on an Air France superjumbo to break apart during a flight between Paris and Los Angeles on Sept. 30, 2017, France’s air-crash authority, Bureau d’Enquetes et d’Analyses, said in a presentation of the accident report on Tuesday.

While the pilots were able to safely land the plane with 521 aboard in Goose Bay, Canada, the subsequent investigation was unprecedented in its scope for an incident that didn’t involve loss of life or a crash, according to the BEA. It cost about 5 million euros ($5.9 million), they said.

The investigators spent nearly two years working with Danish authorities to painsakingly hunt for debris, and finally unearthed a key missing piece of the engine fan hub under 10 feet of snow and ice. The aim was to figure out whether the failure was due to a manufacturing fault or damage incurred during engine maintenance.

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The BEA report concluded that a crack developed underneath the surface due to so-called “cold dwell” fatigue in the metal. The titanium alloy, called Ti-6-4, has been widely used to make aircraft equipment since the 1970s because of its strength and relative light weight.

Unlike other blends, it “had accumulated significant in-service experience without the occurrence of any incident identified as being linked to this phenomenon,” according to the BEA report. The new findings suggest it can occur.

The GP7270 engine was made by Engine Alliance, a joint venture between General Electric Co. and Raytheon Technologies Corp.’s Pratt & Whitney unit. In a statement, the engine maker said it has taken steps to address the BEA’s findings, including updating its systems to account for the cold dwell fatigue issue identified by the investigation.

Airbus and the Engine Alliance both said they supported the inquiry. “Of course there is always a learning in a crisis for all parties,” Airbus said.

Following the accident, regular inspections of the A380 fleet found no cracks in the area of the fan hub considered at risk, and engine manufacturers are considering how to better understand cold dwell fatigue and account for it in future engine designs, according to the BEA.

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“There is a part of bad luck in this, but it can’t be ignored,” BEA director Remi Jouty said. “Every manufacturer should take this into account.”

What spooked investigators is just how close the plane was to disaster, he said. During the split second after the quarter-ton front half of engine No. 4 broke apart, debris flew up and down instead of to the right and left, a direction that would most likely have inflicted ruinous damage to the other engine under the same wing, he said.

“If that had happened, the plane would have gone down,” Jouty said. “It would have been catastrophic.”

The investigation was nearly brought to a halt because of an inability to locate the missing part that finally unlocked the mystery of what caused the engine failure, which occurred at a time when Airbus was still producing the now-halted A380 model. The BEA also had to go back the the manufacturers for funding to continue the search.

French and Danish authorities used satellite imagery, a magnetic sensor that was dragged across the ice sheet, and a type of radar to hunt for the debris in a remote part of Greenland.