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NTSB- SWA CFM56 engine NTSB
A view of the damaged left fan cowl of a Southwest Airlines 737 NG, as seen from the inboard side of the CFM56-7B engine, following the April 2018 in-flight engine failure.

NTSB Orders Corrections for Boeing Jet Engines

Jet builder will address details related to cracked turbine blades, cited as the cause of a April 2018 failure, death of one passenger

The Boeing Co. agreed to correct a design detail on an undetermined number of CFM International CFM-56 engines installed on 737 Next-Generation aircraft, at the direction of the National Transportation Safety Board. Among the actions the OEM described: supporting the engine manufacturers’ recommendations for fan blade inspections; and introducing inlet and fan cowl design changes “to enhance their ability to withstand an engine fan blade out event, as well as to increase the overall capability of these structures.”

The NTSB recommendations result from an investigation into the April 2018 incident aboard a Southwest Airlines flight, in which a part of a fan blade broke loose and broke a passenger window. The incident caused damage to the aircraft, forced an emergency landing, and led to the death of one passenger and minor injuries to seven others.

Last year, following the incident, NTSB ordered inspections of all 737 NG aircraft in service and initiated its evaluation.

The safety board directed a total of seven actions to be taken, including five issued to the Federal Aviation Administration, one to the European Aviation Safety Agency, and one to Southwest Airlines.

Southwest’s entire fleet consists of 737 NG and 737 MAX aircraft. In a statement on the NTSB directive the airline said that safety of its fleet, crews and customers “are of paramount importance.”

The CMF56 engine is a series of high-bypass turbofan engines supplied by CFM International and built by its two joint-venture partners, GE and Safran. It is a predecessor design to the current LEAP engine series. While production of new CFM56 engines ended this year as it is replace by the LEAP, it’s estimated that 7,000 of them have delivered for installation on aircraft around the world.

CFM Intl. issued a statement saying, “Our standard practice is to develop and certify engines in close collaboration with our airframe partners, working within the appropriate regulatory framework. We will continue to strictly comply with regulatory requirements, including any changes that might be adopted as a result of NTSB’s recommendations.”

For Boeing the CFM56 engine issue is distinct from another ongoing safety concern with the 737 NG, involving cracked "pickle fork" components attaching a jet’s fuselage to its wing structure.

And, while both issues concern the 737 NG series, they are separate from the ongoing problem with the 737 MAX series flight-control program.

“All 737 NGs are safe to continue operating normally as the issue is completely mitigated by the fan blade inspections,” Boeing emphasized in its statement. “In addition, Boeing is working on the design enhancements to fully address the safety recommendation from the NTSB. Once approved by the FAA, that design change will be implemented in the existing NG fleet over the longer term. This issue is limited to the 737 NG and does not affect the 737 MAX."

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