Fuel to the engines of the Air India plane that crashed and killed 260 people last month appears to have cut off seconds after the flight took off, a preliminary report has found.

Air India flight AI171 crashed into a densely populated residential area in Ahmedabad on 12 June, killing 241 passengers and 19 others on the ground. It was the deadliest air crash in a decade.

The Boeing 787-8 Dreamliner had been bound for London.

Under international aviation rules, the investigating state must file an initial report with any findings within 30 days of an air crash.

This report found that switches in the cockpit that controlled fuel moved to a “cutoff” position.

It said: “The aircraft achieved the maximum recorded airspeed of 180 knots IAS [indicated airspeed] at about 08:08:42 UTC and immediately thereafter, the engine 1 and engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 1 second.

“The engine N1 and N2 began to decrease from their takeoff values as the fuel supply to the engines was cut off.”

The aircraft started to lose altitude before crossing the airport perimeter wall, it added.

One pilot can be heard on the cockpit voice recorder asking the other why he cut off the fuel. “The other pilot responded that he did not do so,” the report said.

It did not identify which remarks were made by the flight’s captain and which by the first officer, nor which pilot transmitted “mayday, mayday, mayday” just before the crash on 12 June.

The preliminary findings do not say how the switch could have flipped to the cutoff position.

A US aviation safety expert, John Cox, said a pilot would not be able to accidentally move the fuel switches that feed the engines. “You can’t bump them and they move,” he said.

Flipping to cutoff almost immediately cuts the engines. It is most often used to turn engines off once a plane has arrived at its airport gate and in certain emergency situations, such as an engine fire. The report does not indicate there was any emergency requiring an engine cutoff.

“At this stage of investigation, there are no recommended actions to Boeing 787-8 and/or GE GEnx-1B engine operators and manufacturers,” India’s Aircraft Accident Investigation Bureau said.

The report also found that at least five buildings were destroyed when the plane crashed into a densely populated residential area in Ahmedabad.

Nineteen people died on the ground after the plane crashed into a hostel for medical students, the Byramjee Jeejeebhoy medical college and civil hospital, outside the airport.

One section of the report explained how one of the engines was able to restart after transitioning to cutoff, but could not reverse the plane’s deceleration.

Engine 1’s core deceleration stopped, reversed and started to progress to recovery, the report says, while engine 2 was able to relight but “could not arrest core speed deceleration”.

Both of the plane’s black box recorders were located in the days after the crash, one found on 13 June on the rooftop of the building of the crash site, the other on 16 June in the crash debris.

The report appeared to discount the possibility that a bird strike brought the plane down, saying no significant bird activity was observed in the vicinity of the plane’s flight path.

There were 169 Indian nationals, 53 British citizens, seven Portuguese nationals, one Canadian and 12 crew on board the flight.

The sole survivor, Vishwash Kumar Ramesh, a British national, escaped the wreckage through an opening in the fuselage.

Ramesh’s brother Ajay was also on the ill-fated flight but did not survive the tragedy.

Speaking from his hospital bed last month, the 40-year-old said the plane felt like it was “stuck in the air” shortly after takeoff before lights began flickering, adding: “It suddenly slammed into a building and exploded.

“I can’t believe how I came out of it alive. For a moment, I felt like I was going to die too but when I opened my eyes and looked around, I realised I was alive. I still can’t believe how I survived.

“I managed to unbuckle myself, used my leg to push through that opening, and crawled out. I don’t know how I survived,” he said. “I saw people dying in front of my eyes – the air hostesses, and two people I saw near me … I walked out of the rubble.”

Ramesh was one of the pall bearers who carried his brother’s coffin to the crematorium in the town of Diu last month.

An Air India spokesperson said: “Air India stands in solidarity with the families and those affected by the AI171 accident. We continue to mourn the loss and are fully committed to providing support during this difficult time.

“Air India is working closely with stakeholders, including regulators. We continue to fully cooperate with the AAIB and other authorities as their investigation progresses. Given the active nature of the investigation, we are unable to comment on specific details and refer all such enquiries to the AAIB.”

Reuters contributed to this report