A fan blade separated from part of the engine on a Southwest Airlines flight last month, slicing a hole in the left fuselage just above the left wing, federal safety investigators said Monday.
The incident happened Aug. 27 on a flight from New Orleans to Orlando.
The plane, a Boeing 737-700, experienced depressurization and made an emergency landing in Pensacola. Nobody was hurt.
Investigators with the National Transportation Safety Board said they found a hole five inches by 16 inches in the left fuselage.
No material from the fan blade was found in the hole and the cabin was not penetrated, the NTSB said.
The root of the separated fan blade remained in the engine, the report said, but the rest of the blade was not found.
Laboratory tests showed the fracture surface of the missing blade showed small cracks consistent that appeared to come from fatigue.
The blade is made of titanium alloy.
Investigators said they identified an area of fatigue more than an inch long and nearly a quarter-inch deep.
In a short statement, Southwest said the plane had been returned to the airline and repairs were underway.
The statement called the incident "unique and extremely rare."
The NTSB said its investigation was continuing and included reviewing maintenance records.