So much for Boeing’s comeback year. Five days into the new year Dave Calhoun, head of the US aerospace group, finds himself returning to crisis management.

On Friday, an unused emergency exit door — known as a door plug — flew off a Boeing 737 Max 9 plane operated by Alaska Airlines in mid-flight. US regulators immediately ordered 171 of the 217 Max 9 fleet grounded. Boeing shares dropped 7 per cent on Monday.

Under Calhoun, Boeing has tried to return a stalled 737 Max programme following a pair of fatal crashes five years ago. The Max resumed flight in late 2020 but the crisis blackened the company’s reputation and cost it tens of billions of dollars in damages, government fines and lost orders. Rival Airbus has since extended its lead in the lucrative market for single-aisle aircraft.