The FAA grounded all MAX 9s earlier this month following an incident that saw a door blow off an Alaska Airlines 737 MAX 9 in mid-air. Subsequent inspections by operators Alaska and United then discovered loose bolts on a number of other aircraft, which is thought to be the root cause of the problem.

In a new development, the FAA green-lit fresh inspection and maintenance procedures on Wednesday that will allow the trouble aircraft type to return to service.

The process requires an inspection of “specific bolts, guide tracks and fittings” and “detailed visual inspections of left and right mid-cabin exit door plugs”.

Alaska said it planned to put a “few planes” back into service as soon as Friday, while United revealed it was hoping to restart services on Sunday.

The FAA’s decision, though, came alongside it also not granting any production expansion of the entire MAX family of aircraft, including the 9.

“We grounded the Boeing 737-9 MAX within hours of the incident over Portland and made clear this aircraft would not go back into service until it was safe,” FAA administrator Mike Whitaker said.

“The exhaustive, enhanced review our team completed after several weeks of information gathering gives me and the FAA confidence to proceed to the inspection and maintenance phase.

“However, let me be clear: this won’t be back to business as usual for Boeing.

“We will not agree to any request from Boeing for an expansion in production or approve additional production lines for the 737 MAX until we are satisfied that the quality control issues uncovered during this process are resolved.”

Boeing CEO Dave Calhoun told journalists this week the business understood the “gravity of the situation” and insisted it doesn’t put planes in the air that “we don’t have 100 per cent confidence in”.

No Australian carriers currently operate the MAX 9. Virgin Australia and Bonza, though, both operate the shorter MAX 8 variant, with several MAX 10s on order for Virgin.

None of the MAX 8s are affected by the incident, as the model lacks the emergency exit that is sealed by the door plug.

It’s the latest issue to damage Boeing’s reputation over the MAX-branded aircraft after two fatal crashes in Ethiopia and Indonesia killed 346 people.

It resulted in the US Department of Justice fining Boeing US$2.5 billion and accusing the planemaker of “fraudulent and deceptive conduct”, “concealing material information” and “engaging in an effort to cover up their deception”.

“The tragic crashes of Lion Air Flight 610 and Ethiopian Airlines Flight 302 exposed fraudulent and deceptive conduct by employees of one of the world’s leading commercial airplane manufacturers,” said then-acting assistant attorney David P. Burns in 2021.