On Tuesday, Boeing’s president and chief executive Dave Calhoun said the firm was “acknowledging our mistake”.

The door “plug” which fell away from the aircraft weighed 27kg (60lb) and was used to fill an emergency exit that was built into the plane, but not required by Alaska Airlines.

The missing section of the plane was retrieved from the back garden of a Portland teacher, according to the US National Transportation Safety Board (NTSB).

Speaking to Boeing staff, Mr Calhoun said: “We’re going to approach this number one acknowledging our mistake. We’re going to approach it with 100% and complete transparency every step of the way.”

Mr Calhoun reassured staff that Boeing would work with the NTSB to investigate the cause of the accident.