The boss of Boeing has admitted the planemaker was at fault after one of its aircraft suffered a door blow-out shortly after take-off in the US.

No-one was injured when the unused cabin door broke away from the Alaska Airlines flight from Portland, Oregon on Friday.

The US has grounded 171 of the Boeing 737 Max 9 planes since the incident.

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).

It has also been revealed that the airline placed restrictions on the aircraft following pressurisation warnings in the days before the incident, investigators have said.

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.

“They will get to a conclusion… the FAA [Federal Aviation Authority] who has to now deal with airline customers who want airplanes back in service safely and to ensure all the procedures are put into place, inspections, all the readiness actions that are required to ensure every next airplane that moves into the sky is in fact safe and that this event can never happen again,” he said.

The Boeing boss also empathised with those who watched with horror at the footage of the incident: “When I got that picture, all I could think about – I didn’t know what happened so whoever was supposed to be in the seat next to that hole in the airplane. I’ve got kids, I’ve got grandkids and so do you. This stuff matters. Every detail matters.”

Inspections of Boeing 737 Max 9’s are continuing after the FAA said its first priority was “keeping the flying public safe”.