Boeing Jet’s Fiery Engine Blast Came Amid Long Effort for a Fix
Boeing Had Been Redesigning Engine Part Prior to Denver Failure
(Bloomberg) -- Boeing Co. has been working for several years with U.S. regulators on ways to fortify engine covers for at least two of its best-selling jetliners, a redesign that was still underway when one failed last month and rained shredded metal onto a Denver suburb.
The planemaker and the Federal Aviation Administration have been studying ways to reinforce the inlet and engine cowling mounted on the front of jet turbines on at least some 777s and an older 737 family, according to people familiar with the effort and public documents.
The safety review and redesign work were prompted by two 2018 incidents in which shattered fan blades destroyed the front covering of engines, said the people, who asked not to be identified while discussing the matter. That portion of an engine isn’t as heavily fortified to contain flying hunks of metal as the casing surrounding the turbine’s furnace-like core.
That could be changing. The fan blades, which can be more than four feet long, are exposed to enormous pressure during flight. They are essentially the propellers that pull the plane through the air, spinning at several thousand revolutions per minute. When one breaks off it travels with such force it can seriously damage the aircraft and even cause it to crash if it isn’t contained.
Creating a new cowling to contain a broken blade involves extensive design work, mathematical modeling and analysis to validate and eventually certify it. Because federal officials had ordered airlines to step up fan-blade inspections they didn’t consider the shielding design an immediate threat to flight safety.
That was before the dramatic failure on Feb. 20 of a PW4000 engine -- made by the Pratt & Whitney division of Raytheon Technologies Corp. -- on a United Airlines 777-200 that had just taken off from Denver International Airport. Videos of the engine on fire, its front section obliterated, spread rapidly on social media.
Regulators ordered immediate fan blade inspections that effectively grounded the 777s with those engines and said they are considering further steps.
Questions about the adequacy of the cowling could end up prompting costly redesigns or repairs. In addition to the 777, the planemaker is also planning to alter the 737 Next Generation family, the largest in Boeing’s portfolio, with more than 7,000 of the planes built since it was introduced in the late 1990s.
It’s not clear whether Boeing will have to address all of the more than 1,500 777s in service, or only the roughly 130 equipped with the PW4000 engines.
There have been no decisions on whether the existing structures can be fortified or will require a complete replacement, the people familiar with the work said.
While engine manufacturers design the turbine jets themselves, Chicago-based Boeing is responsible for the structures that encase and bind them to the wing.
Boeing declined to comment directly on the redesign work. “Boeing works to ensure that our airplanes are safe and meet all requirements,” the company said in an emailed statement. “We are in constant communication with our customers and the FAA, and engaged in ongoing efforts to introduce safety and performance improvements across the fleet.”
The FAA said it is constantly working with industry to enhance safety. “Any proposed design change to a critical piece of structure must be carefully evaluated and tested to ensure it provides an equivalent or improved level of safety and does not introduce unintended risks,” the agency said in an emailed statement.
In the recent incident above suburban Denver, flying debris caused minor damage to the plane and numerous pieces of metal fell onto neighborhoods. The plane landed safely and nobody was injured. A fracture in a titanium fan blade had grown over time until it broke, according to a preliminary review by the U.S. National Transportation Safety Board.
While concerns over the issue had been reported earlier, the people familiar with it provided new details about the status of the redesign.
Work on a possible redesign of both models began in 2018, according to the people and public records. Early that year there were similar failures: one on another United 777 near Hawaii on Feb. 13; and on a Southwest Airlines Co. 737-700 over Pennsylvania on April 17.
The United plane lumbered safely to Honolulu, but a woman died on the Southwest flight after debris struck the window where she was seated.
Federal law requires that engines are sheathed in an armored casing so that if a fan blade breaks, it and any other debris can’t escape laterally and damage wings, fuel tanks and other critical areas.
The Denver incident was the fifth case in the past five years in which broken fan debris bounced in front of the protective ring, damaging the relatively vulnerable cowling. It had been assumed for decades that any shrapnel would be blown into the engine and spit harmlessly out the rear.
The NTSB was so concerned about the issue that it issued several recommendations in 2019 to the FAA and the European Aviation Safety Agency in its investigation of the Southwest accident. The engine on that plane is made by CFM International Inc., a joint venture between General Electric Co. and France’s Safran SA.
The FAA conducted a risk assessment of the potential for such a failure to occur on the fleet and determined that additional action, such as a legal order by the agency, was needed, it said in a March 9, 2020, letter to the NTSB in response to its recommendations.
An unspecified change in the cowling section of the engine was needed for both the existing fleet and any future planes that are built, the agency said in the letter, which was signed by Administrator Steve Dickson.
“We are working with Boeing to ensure that the corrective action, in the form of a design change, will address the most critical fan blade impact locations,” Dickson wrote.
After the NTSB issued its findings in that case in November 2019, Boeing issued a statement saying it was working on unspecified “enhancements” to the 737 NG cowling.
Similar cowling failures also have occurred on another Southwest 737 in 2016 and on a Japan Airlines 777 last December. In all of the cases involving 777s, the planes have been equipped with PW4000 engines with 112-inch fan sections.
Debate on the need for such a redesign began shortly after the 2018 accidents, said a third person familiar with the work.
One area of focus has been the risks of such a failure on long-distance flights over oceans and other remote regions. The flight that left Denver was headed for Hawaii.
The FAA imposes additional safety measures on these flights to ensure that planes with an engine failure can reach an airport in an emergency. When the cowling comes off an engine, it leads to significantly more drag and officials were concerned such a failure could prompt a plane to run out of fuel before being able to land, the person said.
While enhanced inspections of fan blades are helpful in preventing future failures, they aren’t a perfect measure. Fan blades have failed as a result of striking birds, maintenance errors and other reasons.
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