US airline regulators say they will order inspections on engine fan blades like the one that snapped off and triggered a fatal accident on a Southwest Airlines jet.
The move by the Federal Aviation Administration comes nearly a year after the engine manufacturer recommended the additional inspections, and a month after European regulators ordered their airlines to do the work.
Pressure for the FAA to act grew after an engine on a Southwest jet blew apart on Tuesday, showering the plane with debris and shattering a window. A woman sitting next to the window died of her injuries. The plane made an emergency landing in Philadelphia.
Federal investigators said a blade that broke off in mid-flight was showing signs of metal fatigue - microscopic cracks that can splinter open under the kind of stress placed on jetliners and their engines.
The National Transportation Safety Board also blamed metal fatigue in preliminary findings after an engine broke apart on another Southwest Boeing 737 over Florida in 2016.
That led engine manufacturer CFM International, a joint venture of General Electric and France's Safran, to recommend last June that airlines conduct the inspections of fan blades on many Boeing 737s.
The FAA proposed making the recommendation mandatory in August but never issued a final decision.
In a brief statement late on Wednesday, an FAA official said the agency will issue an order in the next two weeks to require ultrasonic inspection of fan blades on some CFM56-7B engines after they reach a certain number of takeoffs and landings. Blades that fail will have to be replaced, the agency said.
It is not clear how many planes will be affected. Last year, the FAA estimated that an order would cover 220 engines on US airlines. That number could be higher now because more engines have hit the number of flights triggering an inspection.
Southwest announced its own program for similar inspections of its 700-plane fleet over the next month. United Airlines executives said Wednesday that they had begun to inspect some of their planes.
American Airlines has about 300 planes with that type of engine, and Delta Air Lines has about 185. It won't be clear until the FAA issues its rule how many will need inspections.
Tuesday's accident broke a string of eight straight years without a fatal accident involving a US passenger airliner.
"Engine failures like this should not occur," said NTSB Chairman Robert Sumwalt.
Sumwalt expressed concern about such a destructive engine failure but said he would not yet draw broad conclusions about the safety of CFM56 engines or the entire fleet of Boeing 737s, the most popular airliner ever built.
Federal investigators were still trying to determine how a window came out of the plane. The woman sitting next to the window was wearing a seat belt, but passengers said she was partially blown out of the plane. Philadelphia's medical examiner said she died from blunt impact to her head, neck and torso.
Family members identified her as 43-year-old Jennifer Riordan, a banking executive and mother of two from Albuquerque, New Mexico.