Boeing 777 Engine Failures : What You Need to Know

By Kimberly Chin

Investigators continue to probe what caused an engine failure on a United Airlines Holdings Inc. flight headed toward Honolulu from Denver International Airport over the weekend.

Here's what you need to know.

What happened on the flight?

On Feb. 20, United Airlines Flight 328 took off from the Denver airport at 1:04 p.m. local time and climbed to an altitude of about 12,500 feet, according to the National Transportation Safety Board, which is probing the incident. It was then forced to return to the same airport because of engine failure, which left a trail of debris near Broomfield, Colo., a suburb of Denver.

The 26-year-old aircraft had two PW4000-series engines manufactured by Pratt & Whitney, a unit of Raytheon Technologies Corp. None of the 231 passengers and 10 crew members aboard was injured, United said.

What caused the engine failure?

U.S. safety investigators said they found evidence of " damage consistent with metal fatigue" on one of the engine's fan blades that had been largely ripped off. The NTSB, which is the lead agency in the probe, said the loose blade apparently then sheared off part of a second blade that was also fractured. The remaining 20 fan blades showed signs of damage, while the airplane also sustained minor dings and nicks, the safety board said.

Investigators are probing why an outer covering----known as a cowling----detached and why the damaged engine remained on fire even after fuel had been shut off by the flight crew, said Robert Sumwalt, chairman of the NTSB.

Such engine failures, in which internal parts break through the engine's protective casing, can badly damage planes because debris can hit wings, fuel tanks and fuselage. This case will spur more examination because extended flights over water face heightened requirements for maintenance and other safety measures, industry officials said.

Is this type of engine failure common?

In-flight engine failures that spew debris are rare, with three or four occurrences a year world-wide, according to safety agency records.

The recent United engine failure followed at least two similar incidents involving the same type of aircraft and family of engines in recent years.

As a result of the most recent incident in Japan late last year, U.S. air-safety regulators had been considering whether to mandate increased inspections of these engines before the latest failure in Colorado.

Meanwhile, Dutch air-safety investigators are probing the in-flight failure of another Pratt & Whitney engine on a Boeing 747 cargo jet that took off in the Netherlands on Feb. 19, the same day as the latest United incident. The Longtail Aviation jet had a different version of the PW4000 series engine than that used on the Boeing 777 jets.

The 747 landed safely in Liege, Belgium, after losing parts following takeoff that caused minor injuries to two people on the ground and damaged some cars, according to the Dutch Safety Agency.

The FAA said Feb. 21 that it would soon issue an emergency order requiring immediate and stepped-up inspections of certain Pratt & Whitney engines.

What has happened to the planes that use those engines since the latest incident?

The Pratt & Whitney 4000 engines can be found on 128 of Boeing's wide-body 777 aircraft. Boeing has urged airlines to ground those planes while regulators work on a new inspection plan.

Many of the jets Boeing recommended to be sidelined are already in storage. Airlines have mothballed some of the wide-body aircraft they use for long-haul flights because of the coronavirus pandemic, which has curtailed demand for travel.

Sixty-nine of the 777 aircraft with certain Pratt & Whitney 4000-series engines were in service, Boeing said. Most 777 jets have General Electric Co. engines.

Which airlines use these planes?

United is the only airline in the U.S. that uses that engine type, and it has taken two dozen planes out of service. The grounding of the Boeing 777 aircraft would affect a small number of customers, the airline said.

Before Boeing issued its guidance, Japanese regulators had ordered the grounding of 13 Boeing 777s flown by Japan Airlines Co. and 19 operated by All Nippon Airways Co.

Both Korean Air Lines Co. and Asiana Airlines Inc. have grounded all Boeing 777s powered by the Pratt & Whitney 4000 engines that have been in operation, the companies said. Those airlines as well as Jin Air Co. Ltd. have a total of 29 Boeing 777 jets with the P&W engines, according to South Korea's Ministry of Land, Infrastructure and Transport.

Boeing said it was working with U.S. and Japanese regulators, while the engine maker conducts more inspections. Pratt & Whitney said it was working with investigators and airlines on revised engine inspections.

What happened in the previous two incidents?

In February 2018, a United-operated Boeing 777 had an engine failure on its way to Hawaii, and the engine cover was ripped off. The NTSB said the incident was caused by a broken fan blade and that Pratt & Whitney inspectors hadn't correctly identified a sign of a crack in the blade in previous inspections. The NTSB said in a report last year that it found several issues with the training received by Pratt & Whitney inspectors.

The engine maker said it was working to correct those issues and had reviewed inspection records for other fan blades of the same model, the NTSB said in a report. Following that incident, the FAA issued a directive requiring more stepped-up inspections of fan blades on the PW4000 engine type.

In December, a Japan Airlines flight on a 777-200 had an engine failure on a flight bound for Tokyo. The engine was found to have missing and damaged fan blades. Japan Airlines moved on its own after the December engine failure, opting to replace and inspect fan blades on those engines at more frequent intervals than the inspection schedule laid out in the FAA's 2019 directive, a spokesman said.

Japanese authorities deemed the incident a serious one at the time and pressed Japan Airlines and All Nippon Airways to conduct more frequent inspections of aircraft with that engine type. Japan's Ministry of Land, Infrastructure, Transport and Tourism said it has asked U.S. aviation authorities to investigate Saturday's incident and prevent a recurrence.

Write to Kimberly Chin at [e-mail]

(END) Dow Jones Newswires

02-23-21 1546ET