The Max was grounded worldwide in March following two fatal crashes. A probe has centred around one of the aircraft’s deep-seated control systems. Boeing is working on a software update.

Last month, Tui Group chief executive Fritz Joussen said Tui would need to know by the end of May when the Max would be airworthy again if it was to reintroduce its 15 Maxs this summer.

He added there were two scenarios for its Max operations: “July, or not at all for the summer season.”

Iata has since confirmed it does not expect the Max to re-enter service until at least August.

A Tui spokesperson told TTG: “We are ensuring the summer vacations of our guests will take place and we will adjust our fleet planning accordingly, either via wet-lease partners or [changes] in our own fleet. We are prepared for all scenarios.”

Tui estimates costs arising from leasing and other factors would cut annual earnings by 26% (€300 million) if the Max was not to return until the winter season starts in November.

Tui has leased aircraft from at least four airlines to replace its Max flights, while another Max operator, Norwegian, has also had to replace aircraft, although none of these operate to the UK.

Both Norwegian and Tui have previously said they will seek compensation from Boeing for disruption arising from the grounding.