Tui could face a total bill of €500 million if the aircraft’s return to service is further delayed.

Tui said at the start of December that the grounding of the aircraft in March, following crashes involving Indonesia’s Lion Air and Ethiopian Airlines, killing 346 people, had already cost it €293 million.

The operator warned any delay to the return of the aircraft to service would hit it heavily again. It said if the ban was not lifted by end of April 2020, four weeks after summer season flights begin, “the group assumes a further cost of between approximately €220 million to €270 million”.

US officials have now said approval is unlikely before February and could be delayed until March.

Following this, Boeing said it will cut or even halt production of the aircraft after the latest talks with the US Federal Aviation Administration. Boeing added the company “will continue to assess production decisions based on the timing and conditions of return to service”.

American Airlines has, meanwhile, cancelled all Max flights until 6 April. Other carriers also face big disruption and financial costs, which Boeing will eventually have to cover. Ryanair, which operates more than 420 737-800s, which are a different design to the Max, has 135 Max aircraft on order and has had to put next year’s expansion plans on hold.

Ryanair was due to have 58 Maxs by summer 2020 but has now cut planned expansion from 7% to 3%.

Norwegian has 15 grounded Maxs and 88 on order, while Turkish Airlines has 12 grounded and 63 on order. In addition to the disruption, airlines’ fuel costs will also be higher as the Max is 10-15% more fuel-efficient than other 737 types.