Engine Maker Under Scrutiny After Series of Aircraft Mishaps

A recent series of startling airplane engine failures has cast a harsh light on Pratt & Whitney, the storied Connecticut aerospace manufacturer.

The company’s products were involved in two episodes over the weekend in which engines failed in flight, shedding debris over populated areas in Colorado and the Netherlands. In December, the failure of a Pratt & Whitney engine forced a Japan Airlines jetliner to turn around shortly after taking off from Okinawa.

The episodes, which involved Boeing aircraft, all ended in safe landings, and it is too soon to say whether they were connected. But they prompted action by aviation authorities and airlines around the world, raising questions about what went wrong.

“What’s being missed? Is it an inspection cycle? Are they doing proper types of inspections? Are there commonalities between the three failures? Those are the kinds of things that the investigators are going to be looking at now,” said John Cox, an accident investigator and the head of Safety Operating Systems, an aviation consulting firm.

For nearly a century, Pratt & Whitney has occupied an important spot at the center of the U.S. aircraft industry. As well as having huge contracts with civilian airlines, it has for decades supplied engines to the military, including those used in World War II.

Last year, United Technologies, of which Pratt & Whitney was a part, merged with Raytheon, to form Raytheon Technologies. By revenue, Pratt & Whitney is the second largest division at the new Raytheon, bringing in $16.8 billion of sales, accounting for nearly 30 percent of the total.

Pratt & Whitney, which is based in East Hartford, Conn., issued a statement Monday saying it was working with regulators to step up inspections of the engines used to power Boeing 777 jets. It declined to elaborate in response to queries.

The National Transportation Safety Board is leading the investigation into the episode over Colorado on Saturday, in which the right engine on a United Airlines jet bound for Hawaii burst into flames before landing safely in Denver. Like the December flight in Japan, the United episode involved a 777 equipped with a Pratt & Whitney PW4000 series engine.

The incident over the Netherlands, also on Saturday, involved a 747-400 freighter with an engine from the same Pratt & Whitney series, but the aviation authority in Europe said Monday that the specific model was different from those in the Colorado and Japan incidents.

“Nothing in the failure and root analysis show any similarity at this stage,” the aviation authority, the European Union Aviation Safety Agency, said in a statement.

After the United flight’s engine failure, the aviation authority in Japan ordered airlines there to stop flying all 777s similarly equipped. In the United States, the Federal Aviation Administration said it would require increased inspection of planes with those engines. And Boeing called for the 69 planes with that engine model currently in service around the world to be grounded.

Last month, the Japanese Ministry of Land, Infrastructure, Transport and Tourism concluded that the December engine failure was caused by metal fatigue in the fan blades. An initial examination of the United flight found that two parts had separated from the engine and that two fan blades had also fractured, according to the N.T.S.B.

“I was sad to hear that one of the fan blades failed, but really impressed with how everything worked after that,” said Robert Kielb, a professor at Duke University’s school of engineering. “If a blade does fail, the planes are designed to fly on one engine.”

With the 777s flying those engines now grounded, Mr. Kielb said Pratt would need to take a closer look. “They probably need to inspect the fan blades better,” he said. Also of concern was the fact that the cowling — the circular piece on the front of the engine — fell from the sky.

Broken fan blades have led to fatal accidents in the past. In 1989, a Boeing 737 crashed near Kegworth, England, killing 47 people, after a fan blade broke in one engine made by CFM International, and the pilots accidentally cut off fuel to the other engine.

In February 2018, an engine fan blade fractured during a United flight over the Pacific, resulting in an engine failure and loss of the cowling. Like the flight this past weekend, that plane was a Boeing 777 equipped with a PW4077 engine. The pilots were able to land the plane safely, in Hawaii, with no injuries to the 374 passengers and crew on board.

After investigating that episode, the N.T.S.B. placed blame on Pratt & Whitney, saying that one of its inspectors lacked the training needed to catch signs of a faulty blade, resulting “in a blade with a crack being returned to service where it eventually fractured.” In 2019, the F.A.A. ordered further inspections of the fan blades in those engines. More recently, the agency had inspected the fan blade fragment from the Japanese flight and had been considering whether to adjust inspections of the component, it said on Monday.

When airlines buy new planes, they can typically choose which engine to use. In some cases, they may even lease engines from a bank, according to Eric Jones, the chairman of the aviation maintenance science department at Embry-Riddle Aeronautical University.

“They’re very interchangeable,” Mr. Jones said.

United became the first customer of the Boeing 777 in the 1990s and chose to equip the jet with Pratt & Whitney’s new PW4000 engine. All Nippon Airways, another early customer, also chose that engine.

Once a major airline takes possession of a plane, it typically takes over responsibility for routine maintenance and inspections of all parts of the aircraft. Pilots circle planes before each flight, conducting visual inspections, including of the fan blades. Technicians run checks of various systems. When a part like an engine is need of deeper repair or inspection, it is often sent to a third party or the manufacturer itself for a look.

“Boeing does not routinely undertake engine maintenance,” the company said in a statement on Monday. “All decisions beyond published approved manuals are the responsibility of the operator and engine manufacturer.”

It isn’t yet clear what caused the engine fire over the Netherlands, but the Dutch authorities have begun an investigation into the episode there on Saturday.

The plane, a Boeing 747-400 freighter loaded with pharmaceuticals and general cargo and operated by Longtail Aviation, was bound for New York from Maastricht Aachen Airport when air traffic control detected an engine fire and alerted the pilots, the airport said in a statement.

The pilots landed at Liege Airport in Belgium instead of returning to Maastricht Aachen Airport because the runway offered more space to land safely.

During the journey, debris fell over a residential area in the municipality of Meerssen, causing minor injuries to a woman and a child, and leaving “considerable damage to roofs, windows and cars,” said Leon Eummelen, a spokesman for the region’s safety board.

Manufacturers like Pratt & Whitney do not make a lot of money when selling their engines, but the multiyear servicing contracts with airlines have fat profit margins, stock analysts said.

“It’s the classic razor-and-razor-blade business,” said Burkett Huey, an analyst who covers Raytheon Technologies.

The servicing business can be lucrative, and the income from servicing can increase toward the end of an engine’s life as more maintenance is needed. Mr. Huey said Pratt & Whitney and others typically did not reveal exactly how much of their overall profit comes from maintenance.

Isabella Kwai and Claire Moses contributed reporting.

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