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Investigation Points to Metal Fatigue in 737 Engine Failure

Aircraft made an emergency landing at Philadelphia International Airport on April 17.

Bill Carey | Apr 18, 2018

NTSB investigators found evidence of metal fatigue in the left engine of the Southwest Airlines Boeing 737-700 that made an emergency landing at Philadelphia International Airport on April 17 after the pilots initially reported an engine fire, then clarified that there was no fire but that engine parts were missing.

A woman died after an apparent engine explosion blew out a window and caused the cabin to depressurize, nearly pulling her from the aircraft, according to media reports. The passenger fatality was the first on a U.S. airline since 2009.

There were 144 passengers and five crew aboard for Southwest flight 1380, which had departed New York La Guardia Airport for Dallas Love Field. Southwest initially said the flight carried 143 passengers.

At a 9 p.m. briefing at the airport the day of the incident, NTSB Chairman Robert Sumwalt said investigators immediately focused on a missing fan blade in the damaged CFM56-7B turbofan engine. The number 13 fan blade, one of 24 fan blades that draw air into the engine, was broken at the point where it attached to the hub. “Our preliminary examination of this was that there is evidence of metal fatigue where the blade separated,” he told reporters.

The engine cowling was found in Bernville, Pennsylvania, about 70 miles northwest of the airport.

Sumwalt said the NTSB wants to determine if the affected engine part is subject to a pending FAA airworthiness directive (AD) for certain CFM56-7B engines that would require ultrasonic inspections of certain fan blades. The agency proposed the AD after a Southwest 737 experienced a fan blade failure while flying from New Orleans to Orlando in August 2016. The flight crew landed the aircraft safely at Pensacola International Airport.

In June 2017, engine manufacturer CFM International issued a revised service bulletin that recommended one-time ultrasonic inspection of high-time fan blades “as soon as possible” on CFM56-78 engines.

Southwest CEO Gary Kelly informed Sumwalt that the airline will immediately begin enhanced inspection procedures involving ultrasonic inspection on its entire fleet. In a statement posted on its website, Southwest said it will accelerate its existing engine inspection program relating to CFM56 engines “out of an abundance of caution,” a process it expects to complete in 30 days.

CFM, the joint venture of GE Aviation and France’s Safran Aircraft Engines, said the CFM56 engine type entered service in 1997. The FAA issued a certificate of registration to the incident aircraft in 2000. 

During the briefing, Sumwalt provided a timeline of the emergency landing. The flight departed La Guardia Airport at 10:43 a.m. About 20 minutes after takeoff, as the aircraft was passing through 32,500 feet, multiple aural alerts and warnings sounded on the flight deck. The two pilots donned oxygen masks and reported to air traffic control that they had a Number 1 engine fire, were operating on a single engine and were initiating an emergency descent.

“Because they were concerned with potential aircraft controllability issues, they elected to land the airplane with flaps 5 instead of the normal flap setting for a Boeing 737, which would be either flaps 30 or flaps 40,” Sumwalt said. “Once they were on final approach, they clarified to the tower that there was no engine fire, but they were operating single engine and they reported parts of the engine were missing.”

Asked about the significance of the lower flap setting, Sumwalt said: “That would mean that they were going to have a faster approach speed by a good bit, and they did that because of concerns about controllability.”

Sumwalt said the flight crew consisted of a female captain and a male first officer. Media reports identified the captain as Tammie Jo Shults, who was described by friends as one of the first women to fly the U.S. Navy’s F/A-18 Hornet fighter.