The Federal Aviation Administration is investigating claims by a Boeing whistleblower about defects in the 787 Dreamliner

The Federal Aviation Administration is investigating claims made by a Boeing engineer who says parts of the 787 Dreamliner fuselage were improperly fastened together and could break mid-flight after thousands of flights.

Engineer Sam Salehpour, who worked on the plane, detailed his claims in interviews with The New York Times and in documents sent to the Federal Aviation Administration. A spokesman for the agency confirmed that it was investigating these allegations but declined to comment on them.

Salehpour, whose biography says he worked at Boeing for more than a decade, said the problems stem from changes in how large parts are assembled and fastened together on the assembly line. He added that the fuselage comes in several pieces, all from different manufacturers, and they are not the same way they fit together.

Boeing acknowledged making those manufacturing changes, but company spokesman Paul Lewis said there was “no impact on the durability or safe longevity of the airframe.”

Mr. Lewis said Boeing had conducted extensive testing on the Dreamliner and “determined that this was not an immediate flight safety issue.”

“Our engineers are completing complex analysis to determine if there is a concern for long-term fleet fatigue in any area of ​​the aircraft,” Mr Lewis said. “This will not become an issue for the in-service fleet for many years to come, if ever, and we are not rushing the team so we can ensure the analysis is comprehensive.”

In a later statement, Boeing said it was “very confident in the 787 Dreamliner,” adding that “these claims about the structural integrity of the 787 are inaccurate and do not represent the comprehensive work Boeing has done to ensure long-term quality.” “Aircraft safety.”

Mr. Salehpour's allegations add another element to the intense scrutiny Boeing has faced since a door panel on a 737 MAX exploded during an Alaska Airlines flight in early January, raising questions about the company's manufacturing practices. Since then, the plane's manufacturer has announced a major overhaul of its leadership, and the Justice Department has launched a criminal investigation.

Mr. Salehpour's concerns are scheduled to be aired on Capitol Hill. Senator Richard Blumenthal, Democrat of Connecticut and chairman of the Investigations Subcommittee of the Senate Homeland Security and Governmental Affairs Committee, plans to hold a hearing with Mr. Salehpour on April 17. Mr. Blumenthal said he wanted the public to hear directly from the engineer.

“The repeated and shocking allegations about Boeing’s manufacturing failures point to an appalling absence of safety culture and practices — where profit is prioritized over all else,” Blumenthal said in a statement.

The Dreamliner is a wide-body aircraft that is more fuel efficient than many other aircraft used on long-haul flights, partly due to its lightweight composite construction. First delivered in 2011, the twin-aisle plane has fueled a surge in Boeing orders and caused headaches for the company.

For years, the plane manufacturer has dealt with a series of issues with the plane, including battery problems that temporarily grounded 787 planes around the world and quality concerns that recently caused a long pause in deliveries.

Boeing also faced a large number of problems at its plant in South Carolina, where the Dreamliner is manufactured. John Barnett, a prominent Boeing whistleblower who raised concerns about manufacturing practices at the plant, was found dead last month with what appeared to be a gunshot wound.

The Dreamliner pioneered the use of large amounts of so-called composite materials rather than traditional metal to build the aircraft, including major parts such as the fuselage, as the fuselage is known. Composite materials are often made by combining materials such as carbon and fiberglass, which are lighter than metals, but as relatively newer materials, little is known about how they will withstand the stresses of long-term flight. These stresses create what engineers call fatigue, which can compromise safety if it causes the material to fail.

Mr Salehpour said he had been repeatedly retaliated against for raising concerns about shortcuts he believed Boeing was using to assemble the Dreamliner fuselage.

Debra S. Katz, Mr. Salehpour's lawyer, said her client raised his concerns with supervisors and tried to discuss them at safety meetings, but company officials would not listen to him. Instead, it said, Mr. Salehpour was silenced and transferred to work on another wide-body aircraft, the 777. Mr. Salehpour said that after his transfer, he found additional problems with how Boeing assembled the 777 fuselage.

“This is the culture that Boeing has allowed to exist,” Ms. Katz said. “This is a culture that prioritizes aircraft production and pushes them off the line even when there are serious concerns about the structural integrity of those aircraft and their production process.”

Boeing said in its statement that it encouraged its employees to “speak up when problems arise” and that retaliation is “strictly prohibited.”

Ms. Katz said the FAA interviewed Mr. Salehpour on Friday. In response to questions about the Dreamliner, Mike Whitaker, the agency's director, confirmed that the regulator is taking a tough stance against Boeing after the Alaska Airlines incident.

“This will not return to business as usual for Boeing,” Mr. Whitaker said in a statement. “They must commit to making real, profound improvements. Creating fundamental change will require sustained effort from Boeing leadership, and we will hold them accountable every step of the way.

Mr. Salehpour said the shortcuts he believed Boeing was taking resulted in excessive force being used to tighten unwanted gaps in the assembly of parts connecting the Dreamliner fuselage parts. He said the force led to deformation in the composite material, which he said could increase the effects of fatigue and lead to premature failure of the composite.

John Cox, a former airline pilot who runs a safety consulting firm, said that although composites were more tolerant of excess force than metals, it was difficult to see that composites had been stressed to the point that they might fail. “They just explode,” he said.

“Yes, catastrophic disintegration during flight is a theoretical possibility,” Cox said. “That's why you might want to get tested to prevent this.”

Boeing's tests are an appropriate step, Cox said, because “if the degradation becomes severe enough, it could potentially lead to a catastrophic failure.”

Kitty Bennett Contributed to research.