The grounded Boeing 737 Max is unlikely to return to airline schedules this summer.

US carriers American Airlines and Southwest Airlines removed the Max from schedules until June this week after Boeing confirmed it does not expect regulatory approval for the aircraft until the middle of the year.

However, reports the Max could be flying again by mid-year appear overly optimistic after Boeing announced on Tuesday only that the ‘ungrounding’ “will begin during mid-2020”.

Comment: No take-off in sight for Boeing 737 Max

US airlines, which are likely to be the first to put the Max back in the air, estimate it will take one to two months from the date of Federal Aviation Administration (FAA) approval to prepare aircraft for service and to train pilots.

That would delay the aircraft’s return until late August or September even if the aircraft is certified by the end of June.

But while the FAA is expected to lead the way, other regulators – including European aviation safety body EASA – are expected to undertake certification processes of their own, delaying the Max’s return.

Delays beyond mid-summer will further compromise the flying schedule and expansion plans of Ryanair, which was due to take delivery of the first of a substantial 737 Max fleet last year.

It will also increase the costs of flying at Norwegian Air and at Tui, which has 15 of the aircraft and expected to relaunch these from June.

Tui has 60 of the aircraft on order, Norwegian 92 and Ryanair 135.

In a statement, Boeing said: “The FAA and other global regulators will determine when the 737 Max returns to service.

“We are currently estimating the ungrounding of the 737 Max will begin during mid-2020.

“This updated estimate . . . is subject to our ongoing attempts to address known schedule risks and further developments that may arise in connection with the certification process.

“It also accounts for the rigorous scrutiny that regulatory authorities are rightly applying at every step of their review of the 737 Max’s flight control system and the process which determines pilot training requirements.”

Boeing said the announcement aimed “to help customers and suppliers plan their operations” and offered “our best estimate of when regulators will begin to authorise the ungrounding of the 737 Max”.

The company insisted it remains “confident” about “returning the Max safely to service” and said: “We regret the continued difficulties the grounding has presented to customers, regulators, suppliers and the flying public.”

Until late last year Boeing was insisting the Max would be approved by the end of 2019.

The aircraft has been grounded since last March following the crashes of an Ethiopian Airlines Max the same month and a Lion Air 737 in October 2018. The disasters killed 346 passengers and crew.

Boeing halted production of the 737 Max this month, leading suppliers to lay off workers.

New Boeing chief executive David Calhoun, former chairman of the company, took over in January after predecessor Dennis Muilenburg was forced out in December. Calhoun has been on the board of Boeing since 2009.

In a statement the FAA said: “We continue to work with other safety regulators to review Boeing’s work. We have set no time frame for when the work will be completed.”

The FAA has yet to agree to a certification flight for the aircraft. Boeing is due to provide a further update next week.