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

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

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

Both airlines have been forced to cancel hundreds of flights this month as inspections are carried out.

United has said it expects the planes to remain grounded until 26 January and its forecast assumes it won’t be able to fly them at all this month.

The Alaska Airlines flight from Portland, Oregon to Ontario, California, had reached 16,000ft (4,876m) when it began its emergency descent, according to flight tracking data, after the unused emergency exit door blew out.

On Sunday, the FAA said another, older 737-900ER model should also be inspected as they use the same door design. United has 136 of these jets in its fleet.

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

The 737-900ER models have carried out 11 million hours of operations without similar incident to the newer 737 Max 9s.

The FAA did not order the older model to be grounded while the visual inspections are carried out by operators.

Boeing has said it will increase the quality of inspections in its manufacturing processes in wake of the incident.

On Tuesday, United reported flat pre-tax profits of $3.4bn (£2.67bn) for the whole of 2023.

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

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