Southwest Airlines has promised to accelerate inspections of the CFM56-7B turbofans in its fleet of Boeing 737s following early indications of metal fatigue in the engine that blew apart during an April 17 flight from New York La Guardia Airport to Dallas Love Field. The Boeing 737-700 diverted to Philadelphia International Airport, where U.S. National Transportation Safety Board investigators found evidence that one of the fan blades in the left engine separated at its hub attachment point. During the flight, pieces of the engine penetrated a cabin window above the left wing, killing one of the passengers.

The incident appears reminiscent of a 2016 case of uncontained engine failure in another Southwest Airlines 737-700, one of whose CFM56s exploded during a flight from New Orleans to Orlando, Florida. In that case, the NTSB determined that a fan blade separated from the fan disk during the flight due to metal fatigue. Although engine debris created a 5-inch by 16-inch hole in the fuselage just above the left wing, none of the debris penetrated the passenger compartment.

Although, in response, the U.S. Federal Aviation Administration proposed a still pending airworthiness directive requiring ultrasonic inspection procedures for certain CFM56 engines, NTSB chairman Robert Sumwalt told reporters at a press conference in Philadelphia he did not know whether or not the order applied to the engine at the center of the most recent case.