US aviation authorities are to order inspections of jet engines after a mid-air explosion that punctured an airliner's window, killing a passenger.
The Federal Aviation Administration on Wednesday said the "airworthiness directive" will require inspections of a large number of CFM56-7B engines.
Fan blades that have undergone a certain number of flights will be given ultrasonic tests, it said.
A female passenger died after being nearly sucked out of the cabin.
Southwest Airlines Flight 1380, en route from New York to Dallas with 149 people on board, was forced to make an emergency landing at Philadelphia airport on Tuesday.
The CFM56-7B engine is in use on more than 8,000 Boeing 737 planes worldwide, the manufacturer says.
The Federal Aviation Administration (FAA) said its order for engine inspections would be issued within the next two weeks.
Last year, the FAA estimated that some 220 of these engines would require testing, having carried out a certain number of flights.
On Wednesday, other airlines that use planes fitted with the CFM56-7B engine, including United Airlines, American Airlines and Delta Air Lines, said they had begun inspecting some of their aircraft.
An initial investigation found evidence of metal fatigue where a fan blade had broken off, according to the US National Transportation Safety Board (NTSB).
Chairman Robert Sumwalt told reporters that the fan blade had a second fracture about halfway along its length.
He could not say if the incident indicated a fleet-wide issue with the Boeing 737-700.
Mr Sumwalt also said a casing on the engine is meant to contain any parts that come loose but, due to the speed, the metal was able to penetrate the shell.
The Federal Aviation Administration did not say how many engines would be inspected. It said that any fan blades that failed the inspection would have to be replaced.
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