The Federal Aviation Administration (FAA) said it was investigating whether Boeing had failed to make sure that its plane was safe and matched the design approved by the agency.

The FAA said the probe was sparked by the terrifying incident last week, when a Boeing 737 Max 9 operated by Alaska Airlines took off from Portland and lost a fuselage panel. The plane had to make an emergency landing back in Portland. "This incident should have never happened and it cannot happen again," the agency said.

In a letter to Boeing dated 10 January, the FAA said it had learned of other problems with other Boeing 737 Max 9 planes. The letter did not say what the problems were. Alaska and United Airlines, which fly most of the Max 9s in the US, said that they found loose hardware on the panel when they checked their planes.

The new probe is the latest blow for Boeing, which is one of only two makers of big planes for most airlines. The company has been trying to win back the public's trust after two crashes, in Indonesia in 2018 and Ethiopia in 2019, involving the 737 Max 8 killed a total of 346 people.