The warning follows the grounding of Boeing 737-9 Max aircraft after a door plug blew out mid-flight on 5 January. Investigators found missing bolts on the two-month-old Alaska Airlines jet.

After the near-disaster, the US Federal Aviation Administration launched an investigation into the aircraft manufacturer. Following this, FAA administrator Mike Whitaker told Boeing boss Dave Calhoun it needed to make “a systemic shift”.

“Boeing must commit to real and profound improvements,” Whitaker said.

“Making foundational change will require a sustained effort from Boeing’s leadership and we are going to hold them accountable every step of the way, with mutually understood milestones and expectations.”   

The part which failed on the Alaska Airlines flight was assembled by a supplier. The plan means Boeing must ensure the same level of rigour and oversight with its suppliers as it operates itself “and create a measurable, systemic shift in manufacturing quality control”. 

“Boeing must take a fresh look at every aspect of their quality-control process and ensure that safety is the company’s guiding principle,” Whitaker said. 

Production of the Boeing 737 Max is currently halted, which Ryanair, one of its biggest customers, has said will cause issues this year due to the lack of new deliveries.  

Ryanair and Tui operate the Max 8, which is not affected by the door plug issue. The Max 8 was grounded in 2019 following two fatal crashes blamed on faulty software.