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Metallurgy Makes Headlines in Southwest Airlines Incident

April 20, 2018
Source: ASM International

Metal fatigue, metallurgy, ultrasonic inspection, and titanium alloys are in the news the past few days due to a catastrophic engine failure aboard a Southwest Airlines jet. Because ASM International is at the heart of the materials community, many of our members are employees of the organizations involved in investigating this incident and maximizing the safety of air travel and engine designs. We will continue to monitor this story and report on results once the investigation is complete. Included here is a short summary of events as well as links to other news stories and company statements.

On April 17, a crack on a fan blade led to the Southwest Airlines (SWA) disaster that killed one passenger and injured seven others. Because the crack was on an internal surface, it was not detectable by visual inspection, according to National Transportation Safety Board (NTSB) Chairman Robert Sumwalt. NTSB is now investigating why the fan blade came off the widely specified CFM56-7B engine, breaking the engine into pieces and sending metal parts into the 737 jet. The engine is manufactured by CFM International Inc., a joint venture between General Electric Co. and Safran SA.

NTSB investigators will also try to determine if the April 17 incident has any similarities to a 2016 engine failure that occurred on another SWA 737. The 2016 investigation is ongoing, but according to a statement on the NTSB website after the incident, evidence of a crack consistent with metal fatigue in that titanium alloy blade was discovered. In both incidents, the engines were CFM56-7Bs.

On April 17, Southwest announced it was conducting ultrasonic tests of all engines of the same vintage—tests that use ultrasonic sensors to detect cracks beneath the fan blade surface. Testing methods like this are able to detect most flaws before they lead to an explosive failure. However, they are not foolproof according to MIT metallurgy professor Cem Tasan, as quoted in a recent Bloomberg article. “The main problem is none of these techniques will give you a full picture of what is going on in the material,” says Tasan.

Also on April 17, the Federal Aviation Administration (FAA) ruled that Boeing 787 Dreamliners with Rolls-Royce engines could no longer be flown on lengthy over-water flights. This is due to the fact that cracks have developed on some engines used on the Boeing 787 and Boeing 767. An April 19 New York Times article states that the worry is that the flaws are part of a trend as manufacturers push to develop ever more powerful and complex machines. “We’ve gotten smarter,” said Richard Giannotti, an aerospace engineer. “We can design things to a very low margin with a lot of reliability data to back it up. But when we get to the ragged edge, it doesn’t take much for things to go wrong.” He said that in the past, engines were designed with an abundance of precaution. “They don’t do that anymore. They’re trying to whittle down every last bit of material, every bit of weight. Thrust is king.”

With regard to the investigation, a statement on the GE Aviation website reports that GE and Safran Aircraft Engines technicians (about 40 in total) are being deployed to support SWA’s accelerated inspection program related to the CFM56-7B engine, which powers the airline’s Next-Generation 737 fleet. Out of an abundance of caution, the ultrasonic inspections are being conducted on a population of fan blades. Working with Boeing, GE, and Safran Aircraft Engines, SWA expects the accelerated inspections to be completed over the next 30 days. Further, CFM has sent a team of technical representatives to the site to assist the NTSB in its investigation. CFM will support the NTSB and SWA in determining the cause of the accident. CFM and GE will make every resource necessary available to ensure support.

See below for the resources cited in this story. ASM will continue to monitor this story and report on developments.

 

Reference Articles and Links

Metal Weakness in Southwest Jet Tests Limits of Safety Inspections (Bloomberg)

https://www.bloomberg.com/news/articles/2018-04-19/metal-weakness-in-southwest-jet-tests-engineers-skills-to-spot

Engine on Southwest Jet Not the Only One to Develop Cracks (New York Times)

https://www.nytimes.com/2018/04/19/business/engine-on-southwest-jet-not-the-only-one-to-develop-cracks.html

CFM Statement on Southwest Airlines Flight 1380 (CFM website)

https://www.cfmaeroengines.com/press-articles/cfm-statement-incident-wn1380/

Subject Classifications

Industries and Applications | Aerospace and Defense

Materials Properties and Performance | Fatigue

Materials Properties and Performance | Fracture

Materials Testing and Evaluation | Failure Analysis

Materials Testing and Evaluation | Metallography and Microstructures

Materials Testing and Evaluation | Nondestructive Testing

Metals and Alloys | Titanium


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