Crisis-hit Boeing has rushed to defend itself from fresh whistleblower allegations of poor practice, as the airline continues to grapple its latest safety crisis.

A Congressional investigation heard evidence on Wednesday on the safety culture and manufacturing standards at the company – rocked in January by a mid-air scare that saw an Alaska Airlines 737 MAX 9 flight suffer a panel blowout.

One Boeing quality engineer, Sam Salehpour, told members of a Senate subcommittee that Boeing was taking shortcuts to bolster production levels that could lead to jetliners breaking apart.

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He said of Boeing’s 787 Dreamliner, that has more than 1,000 in use across airlines globally including at British Airways, that excessive force was used to jam together sections of fuselage.

He claimed the extra force could compromise the carbon-composite material used for the plane’s frame.

“They are putting out defective airplanes,” he concluded, while adding that he was threatened when he raised concerns about the issue.

The engineer said he studied Boeing’s own data and concluded “that the company is taking manufacturing shortcuts on the 787 programme that could significantly reduce the airplane’s safety and the life cycle”.

Boeing denied his claims surrounding both the Dreamliner’s structural integrity and that factory workers jumped on sections of fuselage to force them to align.

Two Boeing engineering executives said this week that its testing and inspections regimes have found no signs of fatigue or cracking in the composite panels, saying they were almost impervious to fatigue.

The company’s track record is facing fresh scrutiny amid criticism from regulators and safety officials alike in the wake of the incident aboard the Alaska Airlines plane.

It has become a trust issue again after the worst period in Boeing’s history when two fatal crashes, both involving MAX 8 aircraft, left 346 people dead in 2018 and 2019.

All 737 MAX 8 planes were grounded for almost two years while a fix to flawed flight control software was implemented.

A separate Senate commerce committee heard on Wednesday from members of an expert panel that found serious flaws in Boeing’s safety culture.

One of the panel members, MIT aeronautics lecturer Javier de Luis, said employees hear Boeing leadership talk about safety, but workers feel pressure to push planes through the factory as fast as they can.

In talking to Boeing workers, he said he heard “there was a very real fear of payback and retribution if you held your ground”.

Pressure on Boeing to focus on safety has included restrictions placed on production, limiting its manufacturing output.

At the same time, it is still facing three separate investigations by the Federal Aviation Administration, the Justice Department and the National Transportation Safety Board relating to the panel blowout.

A management shake-up announced amid the inquiries will see the chief executive depart the company by the year’s end.

Sky News has approached British Airways for comment.