At the 2015 Paris air show, Dennis Muilenburg seemed to have it all. With his military crew cut, startlingly blue eyes and athlete’s tan, the man about to take over Boeing was bursting with energy about the aerospace and defence company’s future.

Fast forward four years and the crew cut is a little greyer, the complexion paler and the future less certain. Mr Muilenburg is a man under siege. This week the 55-year-old Boeing chief executive was grilled by the US Congress about two fatal crashes of the company’s best-selling 737 Max jet that killed 346 people.

Over two gruelling days, lawmakers interrogated the Boeing chief on evidence that called into question the company’s focus on safety in the drive to get the Max certified for flight, and suggested that staff had been aware for some time of problems with the MCAS anti-stall system cited by investigators as a factor in the incidents.