The two largest operators of the Boeing 737 Max are extending flight cancellations until at least June.

US carriers Southwest Airlines and American Airlines confirmed that the aircraft had been removed from schedules for a further five months.

The measures came after Boeing admitted on Tuesday that it did not expect the aircraft to be cleared by regulators to return to service until the middle of the year.

The 737 Max has been grouded since March last year after two crashes in Indonesia and Ethiopia killed a total of 346 people.

American revealed that around 10,000 flights had been cancelled inits fourth quarter as a result. The airline has 24 Max aircraft and a further 76 on order. It has removed Max flights from its schedule until June 3.

Southwest has 34 of the aircraft type and had expected to have 75 by the end of 2019 and another 38 deliveries in 2020.

The low cost carrier reached a confidential compensation deal with Boeing covering estimated financial damage due to the grounding.

The loss of the aircraft cut $828 million from the airline’s operating income last year and forced the closure of its base at Newark Liberty international airport as New York services were consolidated at LaGuardia airport.

Chairman and chief exective Gary Kelly warned that Max-related flight adjustments were likely to be extended past a recently announced date of June 6.

“Our priority will be to return our 34 grounded 727 Max 8 aircraft in a safe and controlled manner, and we will be prepared to resume deliveries from Boeing on delayed aircraft orders,” he said.

The return of the Max to service is conditional on approval by the US Federal Aviaition Administration.

Kelly said that the airline could “offer no assurances that current estimations and timelines are correct”.

He added: “We remain confident that the Max will return, and once it is cleared to fly, we will add aircraft back into ther schedule at a measured pace that we are comfortable with – operationally, commercially and financially, and with safety top of mind.”