The additional inspections come after the US Federal Aviation Administration said the 737 MAX should remain grounded.

In a letter to the global planemaker’s employees on Monday, Stan Deal, president of Boeing Commercial Airplanes, said the company will also deploy a team to supplier Spirit AeroSystems – which makes and installs the plug door involved in the incident – to check and approve Spirit’s work on the plugs before fuselages are sent to Boeing’s production facilities in Washington state in the US.

Boeing’s quality inspections announcement comes after the US Federal Aviation Administration (FAA) said on Friday that all 737 MAX 9 planes should remain grounded until Boeing provides further data following the near-catastrophic Alaska Airlines incident.

“For the safety of American travellers the FAA will keep the Boeing 737-9 MAX grounded until extensive inspection and maintenance is conducted and data from inspections is reviewed,” the FAA said in a statement.

Only after 40 planes are inspected will the agency review the results and determine whether safety is adequate to allow the MAX 9s to resume flying, the FAA said.

Alaska Airlines also said it was grounding its fleet of 737-9 aircraft for the same reasons.

Deal highlighted that the actions laid out in his letter are separate from the FAA’s ongoing investigation, but said that he planned to increase oversight of MAX production.

He said that in addition to the door plug inspections, Boeing teams will also conduct checks at 50 other points in Spirit AeroSystems’ production process.

Both Boeing and Spirit AeroSystems will also open their 737 production facilities to airline customers for carriers to provide their own inspections.

Boeing will hold sessions for employees on quality management, and bring in an outside party to conduct an independent assessment of its production process, Deal said.

“Everything we do must conform to the requirements in our QMS (quality management system),” Deal said.

“Anything less is unacceptable. It is through this standard that we must operate to provide our customers and their passengers complete confidence in Boeing airplanes.”

Boeing 737 MAX jets have been grounded worldwide in the past. In October 2018 they were grounded for almost two years after a crash in Indonesia killed 189 people, and another in Ethiopia five months later, which killed 157 people.

The aircraft was cleared to fly again after Boeing revamped its automated flight-control system that had activated erroneously in both crashes.