“There are mounting serious allegations that Boeing has a broken safety culture and a set of practices that are unacceptable. These whistleblowers have come forward at great personal risk.”

After its own six-week audit that found numerous issues with Boeing’s quality oversight, the FAA gave the company until late May to deliver a plan for addressing the shortcomings.

The company has pushed back against Salehpour’s allegations, noting that it stopped delivery of the jets for nearly two years after employees raised concerns about small gaps roughly the size of a human hair that existed between the structures in late 2020. On Monday, Fahl and Steven A Chisholm, vice-president for mechanical and structural engineering, briefed reporters on the steps that the company has taken to ensure that the fuselage sections are properly joined and the extensive testing the structures have undergone to make sure they would not fail prematurely. They noted that the FAA signed off on Boeing’s proposed fixes in August 2022, allowing the company to resume delivery of the planes.

While Fahl and Chisholm declined to address specific concerns raised by Salehpour, they expressed confidence in Boeing’s manufacturing, testing and safety oversight process.

Salehpour, however, alleges that after he voiced concerns about 787 jets, he was retaliated against and transferred to work on the 777 programme. He also found problems in that programme, including instances where he said employees forced parts together by using excessive force or, in some cases, jumping on top of components. Chisholm denied workers engaged in such behaviour.

Blumenthal read excerpts from letters sent to his committee by two other Boeing employees, including a former manager at the company’s South Carolina plant, who described a “culture of pressure, shortcuts and hostility”.

Wisconsin Senator Ron Johnson, the committee’s Republican leader, urged more people to come forward as the panel continues to investigate.

“We have to be concerned about what’s happening and we’ve got to get to the bottom of this,” Johnson said.