Metal Fatigue Cited in AirAsia Engine Failure

“Examination of the retained fan blade section identified that the separation was likely due to metal fatigue that originated within the blade’s internal structure.”

Posted: August 28, 2017
By: ehoffman

Aircraft engine with single fractured metal turbine blade
Images of the fractured blade. Credit: avherald.com

The Australian Transport and Safety Bureau (ATSB) has issued its interim report on a scary engine failure that rocked an Airbus A330 in June. AirAsia flight D7-237 was bound for Kuala Lumpur, Malaysia when a fan blade in the plane’s left engine suddenly fractured. Passengers were startled by the loud explosion at 38,000 feet, and pilots shut down the engine prompting a diversion to Perth Airport for an emergency landing.
The plane shook violently during the two-hour return to Australia, and the captain urged passengers to watch the engine and pray for safety. The incident went viral on social media, with videos of the plane “shaking like a washing machine”, and controversy over the pilot’s comments.
We wrote about the incident last month, outlining the dangers of fatigue cracking and the power of laser peening to prevent these critical failures. Now the ATSB has stated publicly for the first time that metal fatigue was the likely culprit.
From the report:
“Examination of the retained fan blade section identified that the separation was likely due to metal fatigue that originated within the blade’s internal structure.”
The engine, a Rolls Royce Trent 772, contains 26 hollow titanium wide-chord fan blades that produce 70,000 pounds of thrust. The blades are designed to be lightweight and powerful, but the extreme tensile stresses of operation can lead to microcracks developing in the metal. If these cracks go undetected, the blade can fail during flight creating a dangerous situation like the one experienced in June by over 350 AirAsia passengers.
Laser peening is applied to fan, turbine, and compressor blades in aircraft engines to prevent this exact scenario. Laser peening imparts deep compressive residual stresses several millimeters beneath the metal surface. Compressive residual stresses offset much of the tensile strain in the component, and a compressive environment impedes the growth of fatigue cracks.
Here’s a video demonstrating how laser peening reduces the tensile stress load on a component, extending the service life 15 times longer than an untreated part.

A full report on the incident is expected to be released next year.
Contact LSPT to learn more about laser peening to prevent costly metal failures.
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