Boeing has moved to replace the 777 engine housings before the recent failures

Because the potential modifications to the outer covers of the 777 engine, commonly known as hoods, presented various shortcomings, “Boeing decided to redesign the fan hood instead of trying to replace existing fan covers to address both structural strength issues.” and humidity issues, according to an internal FAA document reviewed by The Wall Street Journal.

“Boeing will produce new fan covers and provide service instructions for operators to remove and replace fan covers,” according to the document, part of a routine August 6, 2020 update on ongoing efforts at the agency’s Seattle offices. Boeing and the FAA declined to comment on the state of the engine’s coverage plan on Wednesday.

Such modifications to aircraft parts may require years of design, testing, and regulatory approvals. Some aviation safety experts and regulators have become increasingly concerned about whether the engine covers are sturdy enough to withstand the impact of breaking the fan blade and pulling it in flight.

Although rare, such engine cover damage has occurred in a handful of recent engine failures. Pilots train to land a single-engine aircraft that can be done safely, but large pieces of metal on the lids can endanger other parts of the aircraft – and passengers. The engine testing process has not been fully accounted for, according to safety experts and reports from the National Transportation Safety Committee.

Jim Hall, president of the NTSB from 1994 to 2001, said recent incidents should have caused regulators to look “very aggressively” at issues with engine covers.

“We have not yet seen any signs that this has been done,” he said.

Boeing said it would continue to follow the FAA’s guidance on 777 engine covers and was “engaged in ongoing efforts to introduce safety and performance improvements throughout the fleet.”

An FAA spokesman said reducing the risk of engine fan blade failure, which could damage the housing, was a priority – the focus of the agency’s directives following the 777 incidents in 2018 and last week. FAA officials said the agency is working with Boeing on a design change for another type of engine that failed in the 2018 Southwest Flight – killing a passenger – and reviewing the need for changes to other engines.

“Any proposed design change to a critical piece of structure must be carefully assessed and tested to ensure that it provides an equivalent or improved level of safety and does not introduce unintended risks,” the agency spokesman said.

The 777 engine error last weekend came shortly after the plane – as in one of the 2018 incidents operated by United – took off from Denver International Airport. A seemingly weakened fan blade broke and appears to have cut a second blade about in half, according to NTSB, which is conducting the investigation. The engine cover was ripped off, leaving a trail of debris in the city below.

It resembles two recent failures of certain engines manufactured by Pratt & Whitney on a subset of Boeing 777 aircraft – United flight 2018 and one in December 2020 operated by the authorities of Japan Airlines Co. from the US and Japan assigned to both blades that broke and covered the engine covers.

In all three cases, the planes landed safely, without injuries.

Following the 2018 failure of the United 777, the FAA mandated that fan blades on the type of engine involved be subjected to special “thermo-acoustic imaging” inspections –– using sound waves to detect signs of cracks –– every 6,500 flights. The engine that failed over the weekend has made about 3,000 flights since its last inspection, according to people familiar with the problem.

The FAA on Monday ordered immediate thermal-acoustic inspections of fan blade images on certain Pratt & Whitney engines on some Boeing 777 aircraft. Pratt & Whitney is a unit of Raytheon Technologies aerospace company. Body.

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But a design change to strengthen the engine covers is a longer and more involved process. The FAA’s internal document said that Chicago-based Boeing presented FAA specialists in the Seattle area in early August with the 777 engine cover discoveries.

Aircraft engines and their protective covers should contain broken fan blades and other metal parts, preventing them from damaging the structures needed to keep the aircraft up. Detached engine covers that do not fall to the ground could create aerodynamic drag, safety experts said. This could increase fuel consumption if the plane flies less efficiently, a concern for long flights over water with few options for emergency landings, said one of these experts. The FAA mentions “fuel depletion” as a potential safety hazard.

Engine certification tests focused on ensuring that broken fan blades do not pull on the engine side and do not pierce the aircraft’s fuselage. Less attention was paid to the possibility of a blade being able to pull forward and damage the front of the engine covers. Those covers must not be attached during tests on how the motors cope with the broken fan blades so that the blades remain visible.

“When you lose such large parts, it’s a danger,” said Jeffrey Guzzetti, former director of the FAA’s accident investigation division. “There has never been a requirement to consider this before – it has never happened so much.”

Write to Andrew Tangel at [email protected] and Alison Sider at [email protected]