A Boeing whistleblower has claimed that passengers on its 787 Dreamliner could be left without oxygen if the cabin were to suffer a sudden decompression.
John Barnett says tests suggest up to a quarter of the oxygen systems could be faulty and might not work when needed.
He also claimed faulty parts were deliberately fitted to planes on the production line at one Boeing factory.
Boeing denies his accusations and says all its aircraft are built to the highest levels of safety and quality.
The firm has come under intense scrutiny in the wake of two catastrophic accidents involving another one of its planes, the 737 Max – the Ethiopian Airlines crash in March and Lion Air disaster in Indonesia last year.
Mr Barnett, a former quality control engineer, worked for Boeing for 32 years, until his retirement on health grounds in March 2017.
In 2016, he tells the BBC, he uncovered problems with emergency oxygen systems. These are supposed to keep passengers and crew alive if the cabin pressurisation fails for any reason at altitude. Breathing masks are meant to drop down from the ceiling, which then supply oxygen from a gas cylinder.
Without such systems, the occupants of a plane would rapidly be incapacitated. At 35,000ft, (10,600m) they would be unconscious in less than a minute. At 40,000ft, it could happen within 20 seconds. Brain damage and even death could follow.
Although sudden decompression events are rare, they do happen. In April 2018, for example, a window blew out of a Southwest Airlines aircraft, after being hit by debris from a damaged engine. One passenger sitting beside the window suffered serious injuries and later died as a result – but others were able to draw on the emergency oxygen supplies and survived unharmed.
Mr Barnett says that when he was decommissioning systems which had suffered minor cosmetic damage, he found that some of the oxygen bottles were not discharging when they were meant to. He subsequently arranged for a controlled test to be carried out by Boeing’s own research and development unit.
This test, which used oxygen systems that were “straight out of stock” and undamaged, was designed to mimic the way in which they would be deployed aboard an aircraft, using exactly the same electric current as a trigger. He says 300 systems were tested – and 75 of them did not deploy properly, a failure rate of 25%
Mr Barnett says his attempts to have the matter looked at further were stonewalled by Boeing managers. In 2017, he complained to the US regulator, the FAA, that no action had been taken to address the problem. The FAA, however, said it could not substantiate that claim, because Boeing had indicated it was working on the issue at the time.