In February last year, a new Southwest Airlines Boeing 737 Max plane was on one of its first flights when an automated stabilising system appeared to malfunction, forcing the pilots to make an emergency landing soon after they took off. Less than two months later, an Alaska Airlines 737 Max plane with eight hours of total flight time was briefly grounded until mechanics resolved a problem with a fire detection system. And in November, an engine on a just-delivered United Airlines 737 Max failed at 37,000 feet.