Airlines are inspecting Boeing 737 planes after an engine on a passenger flight ripped apart mid-air and killed a woman who came close to being sucked through a broken window.
Jennifer Riordan, 43, was on a Southwest Airline flight from New York to Dallas when a part of the engine shattered into the window and nearly pulled her out.
Mrs Riordan, a banking executive, was hauled back into the aircraft by other passengers who attempted to resuscitate her but she later died of her injuries.
Robert Sumwalt, the chairman of the National Transportation Safety Board (NTSB) said an initial inspection of the failed engine found evidence of metal fatigue where a fan blade had broken off, the Telegraph reported.
Mr Sumwalt said investigators were "very concerned" about the issue of detecting slow-developing metal fatigue. "There needs to be proper inspection mechanisms in place to check for this before there's a catastrophic event."
Jet engine scrutinised
All recent Boeing 737s are powered by engines from CFM, one of the world's largest engine suppliers for commercial planes.
In 2016, another Southwest flight was forced to make an emergency landing after a fan blade separated from the same type of engine, and debris ripped a foot-long hole above the left wing. Metal fatigue was cited in that incident too.
CFM said on Wednesday that there are more than 8,000 of its CFM56-7B engine - the model involved in Tuesday's incident - in operation on Boeing 737 passenger jets.
Southwest, which operates one of the world's largest 737 fleets and has a strong safety record, said it was speeding up inspections of all related engines, which it expected to complete within 30 days.
This month European regulators ordered engine checks following a lengthy analysis of the 2016 Southwest incident but investigators said it is too early to say whether the two problems are linked.
The incident on Tuesday, the first fatal US airline accident in almost a decade, left seven others injured on the 144-passenger plane.
James Healy-Pratt, a pilot and aviation lawyer, said: "Uncontained engine failures are rare but can be devastating. It is where a turbine blade breaks off at high speed within the engine and projects shrapnel through the protective Kevlar engine cowling, designed to stop that.
"The crew did well to get the aircraft down. The question remains how and why the protective Kevlar cowling did not do its job."
Bob Mann, an aviation consultant, said the question was whether current inspection requirements had been met.
"If it is determined to be CFM56-7B fan blade root fatigue failure, as was the earlier 2016 SWA incident...an Airworthiness Directive could be expected from aviation oversight agencies," he said.
He added: "As to the window puncture, despite all simulations, we don't really have a very good idea of where high energy rotating turbine parts will go if they do depart the containment rings and casings, so more attention may be paid to how engine containment is tested and certified as flight-worthy."
Southwest is not inspecting all of its CFM56 engines, instead focusing on older models, according to a source. It is likely its inspections "are in the 400 to 600 engine range in order to wrap this up in 30 days," the source said.