Boeing has moved to replace 777 engine covers before recent breakdowns

Because potential modifications to the 777’s external engine covers, commonly known as hoods, had several shortcomings, “Boeing has decided to redesign the fan hood rather than attempting to modify the existing fan hoods to address both structural strength issues” as moisture problems. internal FAA document reviewed by The Wall Street Journal.

“Boeing will produce new fan hoods and provide service instructions to operators to remove and replace fan hoods,” the document said, which is part of a routine on August 6, 2020, an update on ongoing efforts at the agency’s offices in Seattle. . Boeing and the FAA declined to comment on the status of the bonnet plan on Wednesday.

Such changes to aircraft components can require years of design, testing, and regulatory approvals. Some aviation safety experts and regulators are increasingly concerned about whether engine covers are robust enough to withstand the impact of a fan blade breaking off and ejecting during flights.

While rare, such hood damage has resulted from a handful of recent engine failures. Training pilots to land a plane that runs on one engine, which can be done safely, but large pieces of metal covering can endanger other parts of the plane –– and passengers ––. The engine testing process has not fully anticipated that capability, according to some safety experts and National Transportation Safety Board reports.

Jim Hall, chairman of the NTSB from 1994 to 2001, said recent incidents should have prompted regulators to look “very aggressively” at engine cover issues.

“I have yet to see an indication that this has happened,” he said.

Boeing said it will continue to follow the FAA’s guidelines for 777 engine covers and is “in an ongoing effort to implement safety and performance improvements for its entire fleet.”

An FAA spokesperson said reducing the risk of engine fan blade failure, which could lead to hood damage, has been a priority – the focus of the agencies’ guidelines following the 777 incidents in 2018 and last week. FAA officials have said the agency was working with Boeing on a design change for a different type of engine that failed on the 2018 Southwest flight – which killed a passenger – and was scrutinizing the need for changes to other engines.

“Any proposed design change to a critical part of the structure must be carefully evaluated and tested to ensure that it provides an equivalent or enhanced level of safety and does not involve unintended risks,” said the agency’s spokesman.

The 777’s engine failure last weekend came shortly after the plane took off from Denver International Airport, as in one of the 2018 incidents conducted by United. According to the NTSB, which is leading the investigation, an apparently weakened fan blade has broken off and appears to have shaved a second blade roughly in half. The hood of the engine had ripped off, leaving a trail of debris in the town below.

It looked like two recent failures of certain Pratt & Whitney-made engines on a subset of Boeing 777 aircraft – the 2018 United flight and one conducted in December 2020 by Japan Airlines Co. authorities. in the US and Japan both attributed to fan blades that chipped and battered hoods.

In all three cases, the planes landed safely without any injury.

Following the 2018 outage of the United 777, the FAA mandated that fan blades of the type of engine in question undergo special ‘thermal-acoustic image’ inspections – using sound waves to detect signs of cracking – every 6,500 flights. The engine that went out this weekend had made about 3,000 flights since the last inspection, according to people familiar with the case.

On Monday, the FAA ordered immediate thermal-acoustic image inspections for fan blades on select Pratt & Whitney engines on some Boeing 777 jets. Pratt & Whitney is part of space company Raytheon Technologies Corp.

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But a design change to strengthen engine covers is a longer, more complicated process. According to the FAA internal document, Chicago-based Boeing had presented its findings on the 777 engine cover to FAA specialists in the Seattle area in early August.

Aircraft engines and their guards should contain broken fan blades and other metal parts so that they cannot damage the structures needed to keep the aircraft in the air. Loosened engine covers that don’t fall to the ground can create aerodynamic drag, safety experts say. That could increase fuel consumption if the plane is flying less efficiently, a concern for long flights over water with few emergency landing options, one of these experts said. The FAA document lists “fuel depletion” as a potential safety risk.

The engine certification tests aimed to ensure that broken fan blades do not shoot out of the side of an engine and pierce the fuselage of the aircraft. Less attention has been paid to the prospect that a blade could shoot forward and damage the front part of the hoods. Those covers don’t need to be attached during tests of how motors deal with broken fan blades so that the blades remain exposed.

“Losing such large pieces is a danger,” said Jeffrey Guzzetti, a former director of the FAA’s accident investigation division. “There was never a requirement to consider this before – it just never happened that often.”

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