Bwana Barnett alifanya kazi kwa kampuni kubwa ya ndege ya Marekani kwa miaka 32, hadi alipojiuzulu mwaka wa 2017 kwa sababu za afya.
Tangu mwaka wa 2010, alifanya kazi kama meneja wa ubora katika kiwanda cha North Charleston kinachotengeneza Dreamliner ya 787, ndege ya kisasa sana inayotumiwa hasa kwenye njia za masafa marefu.
Mwaka wa 2019, Bwana Barnett aliiambia BBC kwamba wafanyakazi walio chini ya shinikizo walikuwa wakijaribu kwa makusudi kufunga sehemu duni kwenye ndege kwenye mstari wa uzalishaji.
Alisema pia aligundua matatizo makubwa na mifumo ya oksijeni, ambayo inaweza kumaanisha kwamba moja kati ya maski nne za kupumulia hazitafanya kazi katika hali ya dharura.
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Mr Barnett had worked for the US plane giant for 32 years, until his retirement in 2017 on health grounds.
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.
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 said in some cases, sub-standard parts had even been removed from scrap bins and fitted to planes that were being built to prevent delays on the production line.
He also claimed that tests on emergency oxygen systems due to be fitted to the 787 showed a failure rate of 25%, meaning that one in four could fail to deploy in a real-life emergency.
At the time of his death, Mr Barnett had been in Charleston for legal interviews linked to that case.
Last week, he gave a formal deposition in which he was questioned by Boeing's lawyers, before being cross-examined by his own counsel.
He had been due to undergo further questioning on Saturday. When he did not appear, enquiries were made at his hotel.
He was subsequently found dead in his truck in the hotel car park.
Speaking to the BBC, his lawyer described his death as "tragic".
BBC