Chuck DarwinBoeing whistleblower found dead in US
John Barnett had worked for Boeing for 32 years, until his retirement in 2017.
In the days before his death, he had been giving evidence in a whistleblower lawsuit against the company.
The Charleston County coroner said the 62-year-old had died from a "self-inflicted" wound on 9 March and police were investigating.
From 2010, he worked as a quality manager at the North Charleston plant making the 787 Dreamliner, a state-of-the-art airliner used mainly on long-haul routes.
In 2019, Mr Barnett told the BBC that under-pressure workers had been deliberately fitting sub-standard parts to aircraft on the production line.
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.
Pat Madigan