/United’s Recent Engine Failure Spooked Denver. It’s Happened Before.

United’s Recent Engine Failure Spooked Denver. It’s Happened Before.

When a Boeing 777’s engine cover broke apart and rained parts on a Denver suburb on Feb. 20, the news rang familiar to Christopher Behnam. In February 2018, the 777 he was piloting as captain suffered a similar emergency with the same engine type.

His plane, United Airlines Flight 1175 to Honolulu, was over the ocean 120 miles from the runway carrying more than 370 passengers and crew when a violent blast rocked it.

The jet shook uncontrollably, rolled sharply, and the noise was deafening, said Capt. Behnam. An engine had suffered severe damage. Years of training kicked in, the pilots regained control and shut the engine down. Even so, the plane was hard to handle. A third pilot went into the cabin and looked out the window: The engine hadn’t just failed; its cover had ripped away.

“After the explosion, it felt like she was going to fall apart,” Capt. Behnam said. “I knew I could fly the airplane. The issue was, can I fly it long enough to land it?” The pilots brought the plane to a safe landing in Hawaii.

Capt. Christopher Behnam with failed engine after landing in Honolulu, February 2018.


Christopher Behnam

The National Transportation Safety Board, which investigates U.S. aviation failures, concluded that a roughly 35-pound fan blade broke in the plane’s Pratt & Whitney PW4000 engine due to fatigue, spiraling forward and causing parts of the engine cover to drop into the sea.

Until last month’s Colorado incident involving United Flight 328, the aviation industry and the Federal Aviation Administration had acted only haltingly to address such breakups. That’s despite a series of such failures starting at least five years ago.

Engine “fan blade-outs” are an old problem in aviation. But in recent cases involving Boeing airliners, fast-spinning blade fragments have shot forward into the engine’s inlet, rather than into a protective casing that acts like a bulletproof vest around the sides.

That has resulted in another problem. Engine covers sometimes aren’t surviving those blade fractures, creating bigger hazards for planes, passengers and people on the ground.

A similar engine-cover emergency had hit a Southwest Airlines Co. Boeing 737 flight in 2016. At least three more happened after Capt. Behnam’s flight. Two months after his scare, a Southwest engine cover broke and blasted out a window; a passenger was partially sucked out and died. On Dec. 4, 2020, an engine broke up on a 777 flight near Japan.

Regulators, engine makers and airlines have confronted the problem with a short-term remedy. With varying degrees of urgency in recent years, they have stepped up fan-blade inspections to find pre-fracture cracks that could lead to engine covers ripping off.

Emergency Aloft

In a string of incidents since 2016, engine fan blades have fractured and caused a problem: engine covers ripping off midair. Such a scenario played out on a Boeing 777 bound for Hawaii in 2018:

1. A roughly 35-pound fan blade broke loose due to metal fatigue.

2. Fan-blade fragments caused part of the engine cover to break loose.

2. Fan-blade fragments caused part of the engine cover to break loose.

1. A roughly 35-pound fan blade broke loose due to metal fatigue.

2. Fan-blade fragments caused part of the engine cover to break loose.

1. A roughly 35-pound fan blade broke loose due to metal fatigue.

1. A roughly 35-pound fan blade broke loose due to metal fatigue.

2. Fan-blade fragments caused part of the engine cover to break loose.

Despite working on modifications and replacements for more than two years, plane maker

Boeing Co.

BA 0.13%

, which is responsible for engine coverings on its aircraft, and the FAA have yet to finalize plans to redesign the types of engine covers that have ripped off. “We’ve already seen extreme cases,” said NTSB Chairman

Robert Sumwalt.

“It is something that the industry needs to get on top of and get corrected immediately.”

Complicating the industry’s response to the safety hazard is that it requires coordination among several segments—airplane manufacturers, engine makers, airlines—and among different engineers and regulators focused on avoiding fan-blade fractures and still others focused on preventing engine covers from detaching midair.

In the U.S., that puts the FAA in the best position to tackle the hazard. Its handling of the engine breakups is the regulator’s first big test since its fumbled responses to fatal Boeing 737 MAX crashes in 2018 and 2019.

The FAA declined to make senior agency officials available for interviews. A spokesman said a priority has been reducing the risk of fan-blade failures that can lead to engine covers detaching midair. The FAA spokesman said design changes to a “critical piece of structure must be carefully evaluated and tested” to ensure they provide the same level of safety or better without introducing unintended risks.

Boeing spokesman Bradley Akubuiro said the company “has taken steps to move forward” with the FAA to improve engine covers and is giving its technical teams time they need to ensure any of the manufacturer’s design changes provide their expected performance and maintain overall safety. While designing changes is “exacting and time-consuming,” he said, “this work has been, and remains, a high priority.”

Southwest spokeswoman Brandy King said the airline’s leaders, including Chief Executive

Gary Kelly,

were focused on understanding and learning from the carrier’s fatal accident while working with manufacturers to prevent similar tragedies in the future. Pratt & Whitney and

United Airlines Holdings Inc.

declined to comment.

Planes made by

Airbus SE

haven’t experienced any such engine-cover breakups due to fan-blade fractures in recent years, according to the European Union Aviation Safety Agency, the primary regulator for Boeing’s rival across the Atlantic.

Debris fallen from the United Airlines engine near Denver.


Broomfield Police Department/AFP/Getty Images

Over the past five years, the problem of engine covers detaching due to fan-blade failures that spew parts forward appears to have primarily surfaced on two Boeing aircraft types, the 777 and 737, which use engines made by different manufacturers, according to current and former FAA officials.

To keep fan blades from breaking in the first place, regulators have focused first on stepping up inspections. Within days of the Dec. 4 engine breakup near Japan, Tokyo’s air-safety regulators ordered new engine inspections—visual checks and ultraviolet-light tests, a Japanese aviation official said.

The FAA opted against immediate action and was still considering its next step when the United 777’s engine broke apart near Denver last month. Before that incident, Pratt & Whitney, a unit of

Raytheon Technologies Corp.

, was considering issuing a service bulletin telling airlines to conduct specialized inspections of certain 777 engines every 1,000 flights, said the NTSB’s Mr. Sumwalt. The FAA had required the deep inspections every 6,500 flights after the 2018 incident in Hawaii.

The FAA declined to comment about its response to the December breakup. The agency said it makes safety-oversight decisions in a rigorous, well-established analytical process aimed at quickly identifying and mitigating risk, adding: “To suggest that there is commonality among different events ignores the fact that data for different events is unique to each specific event.”

Early warning

An early warning about the risk that engine covers could crumble when broken blades fly far enough forward came in August 2016. A Southwest flight from New Orleans to Orlando made an emergency landing after an engine failed—a fan blade broke, causing significant damage and leading the cabin to depressurize. One of the engine’s 24 fan blades had broken due to fatigue, NTSB investigators found.

The spinning blade had careened into the front inlet where air flows into the engine. Most of the inlet broke off, spitting debris into the Boeing 737 jet’s fuselage, wing and horizontal stabilizer.

Regulators and industry experts, including at the NTSB, generally viewed that event as a one-off, the NTSB’s Mr. Sumwalt said.

An NTSB investigator examines the Southwest Airlines engine that broke up in 2018.


National Transportation Safety Board

The engine’s manufacturer, CFM International—a joint venture of

General Electric Co.

and France’s

Safran SA

—developed a new, more high-tech inspection protocol using ultrasound technology. A GE spokesman speaking on behalf of the joint venture said the engine maker worked with regulators and customers to enhance and implement inspection procedures and remained committed to working on changes stemming from the NTSB’s recommendations.

The FAA in 2017 considered mandating additional fan-blade testing, though it didn’t require additional checks until the following year when it ordered emergency inspections in the aftermath of the fatal engine-cover breakup on another Southwest flight.

“We determined early that we would require some corrective action and that it was an unsafe condition,”

Christopher Spinney,

an FAA engine specialist, said during an NTSB hearing in 2018. “But we also determined that we had some time.” Mr. Spinney, through an FAA spokesman, declined to comment.

On Capt. Behnam’s flight that year, after the fan blade scattered parts of the 777’s engine cover, the plane’s aerodynamics were out of whack. It felt, he said, like “having an open barn door” on the right side of the plane.

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Two months later on a Southwest 737, debris from an engine covering—again loosened by a broken fan blade—smashed into the plane’s body, blasting out the window through which the passenger was partially sucked.

She was the first U.S. airline-passenger fatality in nearly a decade and Southwest’s first passenger fatality. After the death, Mr. Kelly, Southwest’s CEO, pushed Boeing for an engine-cover fix to avoid a repeat of such a tragedy, according to a person familiar with the plane maker’s work on the 737 engine cover.

After those incidents, the industry began to grapple with vulnerable engine covers. Not only were fan blades failing, they were doing damage to engine coverings that had been expected to withstand such events.

Boeing engineers were particularly concerned about a potential loss of control should engine covers break off and damage a plane’s horizontal stabilizer, said the person familiar with the plane maker’s work.

The damaged engine of United Airlines flight 328.


National Transportation Safety Board/Reuters

Engine makers put their engines through a battery of tests to make sure they will hold together if a fan blade breaks. They are largely focused on making sure debris doesn’t go through the side of the engine casing, where it could penetrate the body of the plane. Broken fan blades can still cause damage by flying forward.

Coverings go through their own certification process on a separate track.

While engine coverings are expected to contain broken fan blades, they aren’t designed to shield more-serious failures of hubs the blades are attached to—as happened on an Airbus A380 jet over Greenland in 2017. Parts fell off at 37,000 feet, damaging buildings but causing no injuries.

Within about two weeks of that incident, the FAA issued an emergency order requiring inspections on roughly 120 of the jets equipped with certain engines produced by Engine Alliance, a joint venture between GE and Pratt & Whitney. GE referred inquiries to Pratt & Whitney, which declined to comment on Engine Alliance’s behalf. An Airbus spokesman said the plane maker takes into account past incidents and accidents, including those on other manufacturers’ aircraft, to enhance safety.

Boeing engineers have been working on a plan to strengthen 737 engine covers, essentially to soften the shock of a fan-blade failure and keep parts attached to the plane even when the blades fly forward, people familiar with the work said.

In March 2020, FAA Administrator

Steve Dickson

told the NTSB the agency was working with the plane maker to strengthen the 737 engine covers, according to written responses to the NTSB’s recommendations. He said the agency would eventually mandate a new design change. The FAA declined to make Mr. Dickson available for an interview.

FAA Administrator Stephen Dickson testifies during a Senate committee hearing last year.


Graeme Jennings/Press Poo

In August 2020, Boeing provided an update to the FAA on its work to also strengthen 777 engine covers. The manufacturer told regulators it had decided to redesign and make replacement covers with which airlines could retrofit their fleets, according to the FAA document.

Boeing’s 777 engine-cover fix didn’t come in time for the Dec. 4 incident near Japan, on a

Japan Airlines Co.

777 with Pratt & Whitney PW4000 engines. Two of an engine’s fan blades broke shortly after takeoff from Okinawa, according to a preliminary report by Japanese investigators. Part of the engine’s cover detached, and the jet’s body and horizontal stabilizer sustained damage, the report said. A JAL spokesman declined to comment on the cause of the incident.

The FAA held off ordering immediate action. After the December incident, the agency said it reviewed the JAL engine’s maintenance and inspection history, conducted a metallurgical exam and was evaluating whether to adjust blade inspections.

It wasn’t immediately clear to investigators and regulators whether the fan-blade cracks at the root of both 777 engine breakups roughly two years apart shared the same underlying cause, according to a person familiar with the FAA’s response. Age, manufacturing defects or maintenance slip-ups can cause metal to crack and eventually fracture. The FAA declined to comment about its work with Boeing on 777 engine covers.

Since the Colorado 777 incident, Boeing has shared some of the changes it is considering to shore up 737 engine covers with carriers including Southwest and

American Airlines Group Inc.,

said people briefed on the matter. It has also been in talks with United about potential changes to 777 engine covers, according to a person familiar with those discussions. Boeing and the FAA declined to comment on when 777 or 737 engine-cover fixes would be completed.

The FAA ordered inspections of some Boeing 777s and the plane maker recommended they be grounded, after an engine on a United jet broke apart in flight. WSJ’s Andrew Tangel reports on how Boeing’s quick response contrasts with its handling of past safety issues. Photo: Chad Schnell via Storyful

Japanese regulators grounded the aircraft the day after the Colorado incident. Soon thereafter, Mr. Dickson ordered immediate specialized inspections even while some FAA officials didn’t believe such drastic action was necessary, said people familiar with the agency’s response.

The move, which the FAA described as “decisive action,” effectively took more than 50 Boeing 777s with certain Pratt & Whitney engines—all operated by United—out of service for months, until inspections have been completed.

Tom Haueter,

a former NTSB director of aviation safety who now consults on safety and accident investigations, said: “They grounded the fleet—that’s about as aggressive as you can get.”

Write to Andrew Tangel at Andrew.Tangel@wsj.com and Alison Sider at alison.sider@wsj.com

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