The U.S. National Transportation Safety Board recommended Tuesday that the Boeing Co. 737 NG be redesigned to prevent a repeat of a fatal incident last year in which an engine part broke off in flight, something the planemaker says it is doing.
More than 7,000 so-called 737 Next Generation planes could be affected by the recommendation that the inlet to the engines be redesigned to contain parts that come loose in a failure.
The safety board issued the recommendation after a hearing Tuesday on the April 17, 2018, incident in which a woman on a Southwest Airlines flight was partially sucked out of the plane and died.
A fan blade on an engine made by CFM International Inc. broke off, triggering the damage, the NTSB concluded.
The NTSB called on the Federal Aviation Administration to require the repair be installed on new 737 NG aircraft and that it be retrofitted onto the thousands of planes in service.
“These recommendations show the way toward greater safety even when a fan-blade-out event occurs,” NTSB Chairman Robert Sumwalt said at the conclusion of the meeting.
Boeing said in an emailed statement that it is introducing enhancements to the part of the engine that failed, to improve its ability to withstand a broken fan blade.
“Boeing is committed to working closely with the FAA, engine manufacturers and industry stakeholders to implement enhancements that address the NTSB’s safety recommendations,” the company said in the statement.
Southwest said in a statement that it looks forward “to reviewing the recommendations of the NTSB and continuing our work with the manufacturers to prevent this type of event from ever happening again.”
The FAA said it will “carefully review and respond to the NTSB recommendations.” Safety is the agency’s first priority, it said in the emailed statement.
Boeing stock slid as much as 2.1% after the NTSB’s comments, but recovered most of that loss. It ended the day down 0.7%.
The NTSB did not ask for changes on other aircraft and engine combinations, but it asked for improvement on how the structure at the front of the engine — a curved surface that provides a smooth flow of air into the power plants — is designed in the future.
The NTSB also urged the European Aviation Safety Agency to adopt the suggested improvements. Although the FAA has no legal authority outside the United States, other nations typically follow its lead.
The NG model is a predecessor to Boeing’s 737 Max, which has been grounded since March after a pair of deadly crashes.
At least part of the reason the April 2018 engine failure caused so much damage is the unusual shape of the structure outside the 737 NG engine. Instead of being circular, as is the case on most models, the NG is flattened on the bottom so the engine can fit on its relatively low wings. It was on that flat section that a hunk of metal broke loose and was flung into the side of the plane, where it struck a window, the NTSB said.
CFM, a joint venture between General Electric Co. and France’s Safran, said it developed the engine’s design in close collaboration with Boeing. “We will continue to strictly comply with regulatory requirements, including any changes that might be adopted as a result of NTSB’s recommendations,” the company said in an emailed statement.
CFM simulated broken fan blades during testing for the engine and didn’t encounter the type of damage that occurred in the 2018 accident, the NTSB said.
Engines are required to be encased in an armored sleeve to prevent debris in a failure from striking the plane, but the structure that hit the window on the Southwest plane was designed by Boeing and was in front of the protected area. Such failures weren’t anticipated during certification and testing, the NTSB said.
The incident on the 737-700 occurred the morning of April 17, 2018, above Pennsylvania on a flight from New York to Dallas. The fractured fan blade started a chain reaction that led a hunk of metal to fly off the jet engine, shatter a window on the plane and trigger an explosive decompression.
The air rushing out of the 737-700 at about 32,500 feet partially sucked 43-year-old Jennifer Riordan through the window, killing her despite other passengers’ attempts to pull her back.
Riordan’s death was the first accident-related passenger fatality on a U.S. airline in more than nine years, and it has raised significant issues about the safety of engines.
Similar failures have occurred at least twice since 2016. A similar cracked blade caused a Southwest 737-700 to make an emergency landing Aug. 27, 2016, near Pensacola, Fla. That plane also lost pressure, but no one was hurt.
Debris also showered a United Continental Holdings Inc. flight from San Francisco to Honolulu on Feb. 13, 2018. The Boeing 777-200, equipped with engines made by United Technologies Corp.’s Pratt & Whitney division, made an emergency landing. There also were no injuries in that episode.
The chaotic emergency descent after the deadly accident also raised questions by the NTSB. Two of the flight attendants on the Southwest plane had to sit on the floor during the emergency landing, partly because they’d moved passengers on the full flight to their jump seats.
The flight attendants should have been in their own seats in case an emergency evacuation or fire occurred, the NTSB said. It also recommended that FAA and Southwest use lessons from the incident to improve the emergency response.