US aviation authorities have ordered inspections of jet engines after a mid-air explosion that punctured an airliner's window, killing a passenger.
The Federal Aviation Administration said the "airworthiness directive" required inspections of certain CFM56-7B engines within two weeks.
Fan blades that have undergone a certain number of flights will be given ultrasonic tests, it said.
A female passenger died after being nearly blown 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, the manufacturer says.
What have investigators said?
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..