Some airlines are reportedly booking passengers on Boeing 737 Max aircraft that remain grounded after two crashes killed 346 people.

Tui Airways, United Airlines and other carriers have scheduled more than 32,600 flights on 737 Max 8 and Max 9 aircraft for later this year despite regulators not yet approving their return to service.

Flight schedules data compiled by flight intelligence specialist OAG show that airlines have started to re-introduce the 737 Max 8s into future schedules, The Sunday Times reported.

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Around 17,512 flights have been set for November and 15,114 for December. Southwest Airlines, American Airlines, Norwegian, United Airlines and Icelandair account for most of these services.

Tui Airways, which has operated the 737 Max from the UK, also has hundreds of flights scheduled on the aircraft in the final two months of the year. Six of Tui’s aircraft remain grounded at Manchester airport.

John Grant, executive vice-president of OAG Aviation, told the newspaper: “Our data shows that airlines are planning to re-introduce the 737 Max from the end of October for their winter schedules.

“This suggests airlines will have taken reassurances from Boeing that the plane is likely to be certified as safe by the US authorities in September or soon after.”

MoreTui suffers deeper winter half-year losses

Boeing grounds 737 Max fleet

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

Boeing chief executive Dennis Muilenburg recently said he expected the Max would be flying again as early as October after a test flight with the US Federal Aviation Administration in September.

The new generation Boeing 737 Max was grounded in March after two crashes. All 189 passengers and crew on a 737 Max 8 operated by Lion Air died shortly after take-off from Jakarta last October. Another 157 people were killed when an Ethiopian Airlines 737 Max crashed just over four months later.

Politicians in the US Senate clashed with FAA officials last month, accusing the regulator of having been too deferential to Boeing in approving the Max and not grounding the aircraft after the first crash last October.

If regulators fail to give the go-ahead for the 737 Max to return to service, airlines will be obliged to lease alternative aircraft or cancel flights – as Norwegian has done with its transatlantic flights from Ireland.

Jim Liu, a flight data analyst for the British publication Airlineroute, said: “Everyone except the passengers are hoping the Max 8 aircraft will take off as soon as possible as they are losing money finding substitute aircraft at the last minute.”

Labour’s transport secretary Andy McDonald reportedly said: “Safety is the number one priority for the aviation industry in the UK and worldwide.

“It’s therefore surprising that a major global airline should seek to pre-empt the findings of international regulators in relation to the safety of the Boeing 737 Max. I know the Civil Aviation Authority will continue to be robust and rigorous in its approach to the safety of these aircraft and their future use in UK airspace.”

British tourist Chuni Kahan said he felt like a “guinea pig” when he discovered last week that his American Airlines flight to the Caribbean would be on a 737 Max 8.

Kahan had booked American Airlines flights between Miami and Puerto Rico ahead of a Caribbean cruise he was planning to take with his wife in December. The airline said at the time that he would be on an earlier model of the 737.

However, American Airlines contacted Kahan last Monday to say that the aircraft scheduled would be a Boeing 737 Max 8.

“The thought of the holiday now sends a shiver down my spine,” Kahan told the newspaper. “I don’t want to be a guinea pig”.

He and his wife have been denied a refund and are planning to buy a new pair of return flights with a different airline.

American Airlines said it had cancelled its 24 Max 8 aircraft until November 2. It also said it would assist customers concerned about flying on the Max once it comes back into service.

MoreTui suffers deeper winter half-year losses

Boeing grounds 737 Max fleet

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