Boeing whistleblower John Barnett is seen in final video before his 'suicide' warning that aviation giant fired quality control inspectors and mechanics 'approved their own work'

A Boeing whistleblower claimed the aviation giant had fired its quality control inspectors and was relying on mechanics shortly before he was found dead in South Carolina on Saturday.

John Barnett, 62, was found with a 'self-inflicted' gunshot wound in Charleston, where he had been in the middle of depositions in a retaliation suit related to production of the 787 Dreamliner plane.

The Charleston Police Department said left a suicide note in his vehicle, as revealed by DailyMail.com. The contents of the note have not yet been revealed.

Just months earlier, in a January appearance on TMZ, he warned that Boeing's 737 planes were being put in the air too soon after the Alaska Airlines midair fuselage blowout on January 5.

Barnett claimed that the incident involving the loose panel was indicative of something greater - and alleged in his lawsuit against the company: Boeing turning a blind eye to safety concerns in order to raise their bottom line. 

'Back in 2012, Boeing started removing inspection operations off their jobs... So, it left the mechanics to buy off their own work.'' he told TMZ, recalling his time as a quality overseer at Boeing's SC plant, which manufactured 787s.

Boeing whistleblower John Barnett claimed the aviation giant had fired its quality control inspectors and was relying on mechanics shortly before he was found dead on Saturday

Barnett said he had problems with  how Boeing was handling its production of its 737s and 787s in particular, days after a door plug blew out on a 737 blew out at 16,000ft

In January, Barnett explained why he believed both models were ticking time bombs, as both incidents remain under investigation

Barnett was found dead inside his truck on Saturday in the parking lot of a Holiday Inn in Charleston, pictured above

Barnett added: 'What we're seeing with the door plug blowout is what I've seen with the rest of the airplane, as far as jobs not being completed properly, inspection steps being removed, issues being ignored.

'My concerns are with the 737 and 787, because those programs have really embraced the theory that quality is overhead and non value added.

'I know the FAA is going in and done due diligence and inspections to ensure the door close on the 737 is installed properly and the fasteners are stored properly,' he said, citing the parts that likely played a part in the incident.

'But, my concern is, "What's the rest of the airplane? What's the condition of the rest of the airplane?"'

Barnett's suit against Boeing alleged under-pressure workers were deliberately fitting 'sub-standard' parts to Boeing 787s, and that brass were sweeping defects under the rug to save money.

It also emerged Monday that an FAA review found that Boeing had failed 33 of 89 product audits conducted. 

Boeing shed $4billion in value overnight after news of Barnett's death and the FAA audits.

Shares dropped by more than 4 percent Tuesday morning, as the airline maker's stock slumped to a five-month low.

It follows weeks of scandals since a door plug blew out on an Alaska Airlines flight on January 5. Since then, Boeing's value has nosedived from $150billion to $112billion. 

Barnett had spoken to media outlets following the January 5 incident on a Boeing 737 MAX 9 plane, when a panel blew out while the flight was in mid-air, exposing passengers to the outside air that required an emergency landing.

Boeing has since had to reckon with a full-blown crisis around its safety and quality standards.

Its production has been curbed by U.S. regulators, leading to delivery delays across the aerospace industry.

Shares for Southwest Airlines also dipped, by 13 percent, after the company said it would limit its capacity plans and reevaluate financial forecasts for this year.

Southwest said on Tuesday that Boeing informed them they would deliver 46 Boeing 737 Max 8 planes this year, down from the original planned 58.

The first months of the year have been full of scandals involving Boeing, including several terrifying near-tragedies on air, beginning with the Alaska Air January incident.

On Thursday, a wheel fell off a Boeing 777-200 shortly after takeoff in San Francisco.

Shares dropped by more than 4 percent Tuesday morning as the aviation giant's stock slumped to a five-month low on the news late Monday that John Barnett was found dead in a hotel parking lot in Charleston, SC, on Sunday 

Since a door plug blew out on an Alaska Airlines flight on January 5, Boeing's value has nosedived from $150billion to $112billion

The 256lb wheel fell from a United Airlines plane shortly after take-off and crushed cars parked below after it plummeted to the ground.

On Monday, just days before the wheel incident, a 737 engine caught fire mid-flight.

The terrifying incident took place just minutes into a United Airlines flight bound for Fort Myers, Florida.

Video taken from a passenger window shows white-hot flashes streaming out of the 737's jet engine.

Earlier this week, the head of the National Transportation Safety Board accused Boeing of failing to provide some key records sought in its ongoing investigation into the Alaska Air mid-air cabin door emergency.

NTSB Chair Jennifer Homendy said investigators have sought the names of the 25 people who work on door plugs at a Boeing facility in Renton, Washington, but have not received them from Boeing.

'It is absurd that two months later we don't have it,' Homendy said at a Senate Commerce Committee hearing on Wednesday.

Boeing insisted that it had initially provided the NTSB with some of the names of Boeing employees, including door specialists it believed would have relevant information.

Senator Ted Cruz, the top Republican on the Commerce Committee, called it 'utterly unacceptable' that the NTSB was not receiving full cooperation from Boeing.

Homendy also confirmed that the MAX 9 door plug had moved during prior flights, citing markings on the door.