A major US airline has said it will lose money in the three months between January and March due to grounding of Boeing 737 Max 9 jets.

The US Federal Aviation Administration (FAA) grounded 171 of them after an unused door broke mid-flight.

United Airlines has 79 aircraft on its fleet, more than any other carrier, followed by Alaska Airlines.

Both airlines have been forced to cancel hundreds of flights this month as the investigations take place.

United has told It expects flights to be grounded until January 26 and its forecast assumes no flights for the rest of the month.

An Alaska Airlines flight from Portland, California to Ontario, reached an altitude of 16,000 feet (4,876 m) when it began an emergency descent after an unused emergency exit door exploded, according to flight tracking data.

In a statement on Sunday, the company said: “The safety of the flying public, not speed, will determine the timeline for returning these aircraft to service.”

The 737-900ER models have logged 11 million hours of operation without incident, like the new 737 Max 9s.

The FAA does not mandate that older models be grounded while visual inspections are performed by operators.

In the wake of the incident, Boeing said it was stepping up inspections of its manufacturing processes.

On Tuesday, United reported a pre-tax profit of $3.4bn (£2.67bn) for the full year 2023.

United will discuss the results of a call with analysts and investors on Tuesday morning, when the company is expected to provide an update on safety inspections of the grounded planes.

Both Alaska and Boeing are scheduled to report their results in the next two weeks.