Another Southwest Airlines plane's engine shredded due to metal fatigue about two years before Tuesday's mishap aboard a New York-to-Dallas flight left one woman dead and seven others injured.
In 2016, a Southwest Airlines Boeing 737-700 blew an engine as it flew from New Orleans to Orlando, Florida, and shrapnel tore a 5-by-16-inch hole just above the wing. The plane landed safely. The National Transportation Safety Board said a fan blade had broken off, apparently because of metal fatigue.
That case bears some resemblance to Tuesday's accident, which nearly sucked out of depressurized cabin and forced the pilot to make a rapid descent in order to make an emergency landing in Philadelphia.
Based on a preliminary examination, the NTSB said there was evidence of "metal fatigue" in the engine. NTSB chairman Robert Sumwalt said one of the jet's fan blades was separated at the point where it would come into the hub.
Sumwalt says part of the engine covering was found in Bernville, Pennsylvania, about 70 miles west of Philadelphia. One of the fan blades was missing, however.
In both cases, the planes had the same engine model manufactured by CFM International. NBC 4 New York has reached out to CFM about the incidents, but in a statement relating to Tuesday's mishap the company said the model has "an outstanding safety and record since entering revenues service in 1997 while powering more than 6,700 aircraft worldwide."
Southwest said Tuesday it expects to finish inspections of the engines over the next 30 days. It says it's making the move out of caution, and it's not clear how many planes in the airline's fleet of 737s use those engines.
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Images from both incidents also bear similarities, with the front housing on both engines apparently blown off.
Last year, the engine maker and the Federal Aviation Administration instructed airlines to make ultrasonic inspections of the fan blades of engines like those on the Southwest jet. The FAA said the move was prompted by a report of a fan blade failing and hurling debris. But it was unclear whether the particular engine that failed on Tuesday was covered by the directives.
