Attorneys representing the Boeing employee-turned-whistleblower, who was discovered deceased in what appears to be a suicide, have praised him as "a courageous and principled individual of the utmost integrity".

Authorities are presently investigating the passing of John Barnett, which seemed to result from a self-inflicted injury.

Having retired from Boeing in 2017 after over three decades of service, Mr. Barnett was providing testimony in a lawsuit against the company before his demise.

In a statement to the BBC, two of his legal representatives urged law enforcement to thoroughly scrutinize the circumstances surrounding his death.

"John was actively engaged in giving his testimony in the whistleblower retaliation case, which was nearing its conclusion," remarked Robert Turkewitz and Brian Knowles. "He was in high spirits and eager to move past this chapter of his life. There were no signs indicating he would take such drastic action. It's unimaginable."

Calling for transparency from officials in Charleston, South Carolina, they emphasized, "Every aspect of this situation must be thoroughly examined."

Turkewitz and Knowles emphasized that Mr. Barnett held a deep affection for his family, friends, and Boeing, demonstrating a commitment to everyone associated with the company, from its pilots to its clientele.

Between 2010 and his retirement due to health reasons, Mr. Barnett served as a quality manager at the North Charleston plant involved in the production of the 787 Dreamliner, an advanced aircraft predominantly utilized for long-distance flights.

In that job, he "learned of and exposed very serious safety problems with the Boeing 787 Dreamliner and was retaliated against and subjected to a hostile work environment", his lawyers said.

After retiring, he embarked on a long-running legal action against the company.

He accused it of denigrating his character and hampering his career because of the issues he pointed out - charges rejected by Boeing.

At the time of his death, Mr Barnett had been in Charleston for legal interviews linked to that case and he gave a formal deposition last week in which he was questioned by Boeing's lawyers, before being cross-examined by his counsel.

He had been due to undergo further questioning on Saturday. When he did not appear, inquiries were made at his hotel.

He was subsequently found dead in his truck in the hotel car park.

Taking on his long-time employer had caused Mr Barnett to develop post-traumatic stress disorder (PTSD) and his health had been in decline, his brother told US media.

"He was suffering from PTSD and anxiety attacks as a result of being subjected to the hostile work environment at Boeing, which we believe led to his death," Rodney Barnett said.

Mr Barnett added that his brother "was looking forward to having his day in court and hoped that it would force Boeing to change its culture".

The quality manager was known for raising concerns about the US plane giant's production standards, telling the BBC in 2019 that under-pressure workers had been deliberately fitting sub-standard parts to aircraft on the production line. He later told the BBC that workers had failed to follow procedures intended to track components through the factory, allowing defective components to go missing.

He also said he had uncovered serious problems with oxygen systems, which could mean one in four breathing masks would not work in an emergency.

He said soon after starting work in South Carolina he had become concerned that the push to get new aircraft built meant the assembly process was rushed and safety was compromised, something the company denied.

Mr Barnett said he had alerted managers to his concerns, but no action had been taken.

Boeing denied his assertions. However, a 2017 review by the US regulator, the Federal Aviation Administration (FAA), did uphold some of Mr Barnett's concerns.

It established that the location of at least 53 "non-conforming" parts in the factory was unknown and that they were considered lost.

On the oxygen cylinders issue, the company said that in 2017 it had "identified some oxygen bottles received from the supplier that was not deploying properly". But it denied that any of them were fitted on aircraft.

Mr Barnett's death comes at a time when production standards at both Boeing and its key supplier Spirit AeroSystems are under intense scrutiny.

Last week, the FAA said a six-week audit of the company had found "multiple instances where the company allegedly failed to comply with manufacturing quality control requirements".