The U.S. Federal Aviation Administration said it will order inspections of about 220 aircraft engines after investigators found that a broken fan blade triggered an engine explosion this week on a Southwest flight, killing a passenger. The regulator said late on Wednesday that it plans to finalize the airworthiness directive within the next two weeks. The order, initially proposed in August following a 2016 incident, will require ultrasonic inspection within six months of the fan blades on all CFM56-7B engines that have exceeded a specified number of takeoffs. Airlines said that because fan blades may have been repaired and moved to other engines, the order would affect far more than 220 CFM56-7B engines, which are made by a partnership of France’s Safran and General Electric. The CFM56 engine on Southwest 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 into the fuselage of the Boeing 737-700 and shattered a window. Bank executive Jennifer Riordan, 43, was killed when she was partially pulled through a gaping hole next to her seat after the cabin suffered rapid decompression. Fellow passengers pulled her back inside, but she died of her injuries. National Transportation Safety Board Chairman Robert Sumwalt said the incident began when one of the engine's 24 fan blades snapped off its hub; investigators found the blade had suffered metal fatigue at the attachment point and a second fracture about halfway along its length. Sumwalt said the fatigue would not have been observable from the outside. He could not yet say whether the accident, the first deadly U.S. airline accident since 2009, indicates a fleet-wide problem with the Boeing 737-700. Southwest inspected similar CFM56 engines in service, focusing on the 400 to 600 oldest engines. The failure, the second such engine failure on a Southwest jet in two years, prompted airlines worldwide to step up inspections. An NTSB crew also combed the Boeing 737-700 for signs of what caused the engine to explode, and investigators tracked debris on radar to rural Pennsylvania. Passengers described scenes of panic after a piece of shrapnel from the engine shattered a plane window, almost pulling Riordan out. Riordan was a Wells Fargo (WFC.N) banking executive and well-known community volunteer from Albuquerque, New Mexico, the company said. Videos posted on social media showed passengers grabbing for oxygen masks and screaming as the plane, piloted by Tammie Jo Shults, a former U.S. Navy fighter pilot, prepared to descend into Philadelphia. Southwest expected to complete inspections of the targeted engines 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, which covers its inner workings, were found about 60 miles (100 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 FAA last year to propose ultrasonic inspections of similar fan blades and to replace any that failed.