Boeing removed executive Ed Clark, the head of its 737 Max passenger jet program, in the wake of several safety and quality-related incidents.

The 737 Max is Boeing’s best selling plane, but has been a source of repeated problems over the last five years, starting with a 20-month grounding in 2019 and 2020 following two crashes that killed a total of 346 people. More recently, a door plug on a Boeing 737 Max flown by Alaska Airlines blew out soon after taking off, leaving a gaping hole in the side of the plane.

A preliminary report by the National Transportation Safety Board found that the four bolts that should have held the door plug in place were missing when the plane left Boeing’s factory.