(Reuters) - The U.S. Federal Aviation Administration said on Wednesday it would order inspection of some 220 jet engines after investigators said a broken fan blade touched off an engine explosion on a Southwest Airlines flight, shattering a window and killing a passenger.

The order, called an air-worthiness directive, would require an ultrasonic inspection within the next six months of the fan blades on all CFM56-7B engines that have accrued a certain number of takeoffs.

The CFM56 engine on Southwest LUV.N flight 1380 blew apart over Pennsylvania on Tuesday, about 20 minutes after the Dallas-bound flight left New York's LaGuardia Airport with 149 people on board.

The explosion sent shrapnel ripping into the fuselage of the Boeing 737-700 plane and shattered a window.

Bank executive Jennifer Riordan, 43, was killed when she was partially pulled through a gaping hole next to her seat in row 14 as the cabin suffered rapid decompression. Fellow passengers were able to pull her back inside but she died of her injuries later on Tuesday.

Philadelphia’s medical examiner ruled that the cause of death was blunt trauma to the head, neck and torso, and ruled the death an accident, spokesman Jim Garrow said.

“As captain and first officer of the crew of five who worked to serve our customers aboard Flight 1380 yesterday, we all feel we were simply doing our jobs. Our hearts are heavy,” Captain Tammie Jo Shults and First Officer Darren Ellisor said in a statement released by the airline.

Shults and Ellisor said they were focussed on working with investigators and would not be speaking to the media.

Earlier on Wednesday, National Transportation Safety Board Chairman Robert Sumwalt told a news conference that the incident began when one of the engine’s 24 fan blades snapped off from its hub. Sumwalt said investigators found that the blade had suffered metal fatigue at the point of the break.

Sumwalt said he could not yet say if the incident, the first deadly airline accident in the United States since 2009, pointed to a fleet-wide issue in the Boeing 737-700.

“We want to very carefully understand what was the result of this problem, and as I mentioned a few minutes ago, I’m very concerned about this particular event,” Sumwalt said at the news conference at the Philadelphia airport.

“To be able to extrapolate that to the entire fleet, I’m not willing to do that right now.”

Southwest crews were inspecting similar engines the airline had in service, focussing on the 400 to 600 oldest of the CFM56 engines, made by a partnership of France's Safran SAF.PA and General Electric GE.N, according to a person with knowledge of the situation. It was the second time that kind of engine had failed on a Southwest jet in the past two years, prompting airlines around the world to step up inspections.

A National Transportation Safety Board inspection crew was also combing over the Boeing BA.N 737-700 for signs of what caused the engine to explode.

Sumwalt said the fan blade, after suffering metal fatigue where it attached to the engine hub, suffered a second fracture about halfway along its length. Pieces of the plane were found in rural Pennsylvania by investigators who tracked them on radar. The metal fatigue would not have been observable by looking at the engine from the outside, Sumwalt said.

The FAA said late on Wednesday it would finalise the airworthiness directive it had proposed in August within the next two weeks.

Although the FAA said the directive would apply to about 220 engines, airlines said that because fan blades may have been repaired and relocated, it would affect a far greater number.

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The jet was travelling at 190 miles per hour (305 kph) when it made an emergency landing at Philadelphia International Airport, according to Sumwalt, much faster than the typical 155-mile-per-hour touchdown.

Passengers described scenes of panic as a piece of shrapnel from the engine shattered a plane window, almost sucking Riordan out.

“The window had broken and the negative pressure had pulled her outside the plane partially,” Peggy Phillips, a registered nurse who was on the plane, told WFAA-TV in Dallas. “Two wonderful men ... they managed to get her back inside the plane, and we laid her down and we started CPR.”

Riordan was a Wells Fargo WFC.N banking executive and well-known community volunteer from Albuquerque, New Mexico, the company said.

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“MY LAST FEW MOMENTS”

Videos posted on social media showed passengers grabbing for oxygen masks and screaming as the plane, piloted by Shults, a former U.S. Navy fighter pilot, prepared for the descent into Philadelphia.

“All I could think of in that moment was, I need to communicate with my loved ones,” passenger Marty Martinez told ABC’s “Good Morning America” on Wednesday. During the incident, he logged on to the in-flight Wi-Fi to send messages to his family.

“I thought, these are my last few moments on Earth and I want people to know what happened,” said Martinez, who live-streamed on Facebook images of passengers in oxygen masks as the plane made a bumpy descent into Philadelphia.

Southwest Airlines experienced an unrelated safety incident early on Wednesday when a Phoenix-bound flight was forced to land at the Nashville airport shortly after takeoff because of a bird strike.

The airline expected to wrap up its inspection of the engines it was targeting in about 30 days.

The GE-Safran partnership that built the engine said it was sending about 40 technicians to help with Southwest’s inspections.

Pieces of the engine including its cowling - the smooth metal exterior that covers its inner workings - were found about 60 miles (97 km) from Philadelphia airport, Sumwalt said. The investigation could take 12 to 15 months to complete.

In August 2016, a Southwest flight made a safe emergency landing in Pensacola, Florida, after a fan blade separated from the same type of engine and debris ripped a hole above the left wing. That incident prompted the U.S. Federal Aviation Administration to propose last year that similar fan blades undergo ultrasonic inspections and be replaced if they failed.