An official report on the world’s deadliest aviation accident in a decade has answered one key question – but raised others.

Air India flight AI171 had barely left the runway last month when it lost momentum and crashed in a densely populated area of India’s western city of Ahmedabad, killing all but one of the 242 people on board and 19 others on the ground.

Now, a preliminary report by India’s Aircraft Accident Investigation Bureau (AAIB) has revealed that fuel supply to both engines was cut in the crucial minutes as the aircraft was ascending.

The plane’s “black box,” its flight data recorder, showed that the aircraft had reached an airspeed of 180 knots when both engines’ fuel switches were “transitioned from RUN to CUTOFF position one,” the report says. The switches were flipped within a second of each other, halting the flow of fuel.

On an audio recording from the black box, mentioned in the report, one of the pilots is heard asking the other why he flipped the switches. The other pilot responds that he did not do so. The report does not specify who was the pilot and who was the co-pilot in the dialogue.

Seconds later, the switches on the Boeing 787 Dreamliner were flipped the other way to turn the fuel supply back on. Both engines were able to relight, and one began to “progress to recovery,” the report said, but it was too late to stop the plane’s gut-wrenching descent.

The report reveals the fundamental reason why the jet crashed, but much remains unexplained.

Kalpeshbhqi Patni cries out as he waits outside a hospital in Ahmedabad, India, on Friday, June 13. His brother Akash died in the plane that crashed there the previous day. Adnan Abidi/Reuters Security personnel walk near damaged buildings at the crash site on Friday. Adnan Abidi/Reuters Indian Prime Minister Narendra Modi visits the crash site on Friday. Press Information Bureau/Anadolu/Getty Images Hospital staff load the body of a plane crash victim into a vehicle at the Civil Hospital in Ahmedabad on Friday. Amit Dave/Reuters People gather near the site of the crash on Thursday, June 12. Amit Dave/Reuters Search-and-recovery teams work through the rubble on Thursday evening. Ajit Solanki/AP Security guards stand at the crash site. Elke Scholiers/Getty Images The interior of the building where the plane crash-landed. Ajit Solanki/AP Health officials wait to take DNA samples from the family members of plane crash victims on Thursday. Adnan Abidi/Reuters Dabu Patni cries upon learning that her brother Akash was aboard the plane that crashed. Amit Dave/Reuters Rescue officials work at the site of the crash. Sam Panthaky/AFP/Getty Images A firefighter works at the crash site. Sam Panthaky/AFP/Getty Images Thursday’s crash marks the first involving a Boeing 787 Dreamliner since the aircraft first entered into service in 2011, according to Boeing’s Statistical Summary of Commercial Jet Airplane Accidents. Amit Dave/Reuters Rescue team members work at the site of the plane crash. Amit Dave/Reuters Officials work at the crash site. Sam Panthaky/AFP/Getty Images The tail of the airplane is stuck in a building. Ajit Solanki/AP A police officer stands in front of the wreckage. Adnan Abidi/Reuters People work at the crash site. Ajit Solanki/AP Rescuers carry a victim’s body. Ajit Solanki/AP People stand around the debris of the airplane. Ajit Solanki/AP In pictures: Passenger plane crashes in India Prev Next

From RUN to CUTOFF – but how?

The findings do not make clear how the fuel switches were flipped to the cutoff position during the flight, whether it was deliberate, accidental or if a technical fault was responsible.

On Boeing’s 787 Dreamliners, the fuel switches are between the two pilots’ seats, immediately behind the plane’s throttle levers. They are protected on the sides by a metal bar.

The switches require an operator to physically lift the switch handle up and over a detent – a catch – as they are deliberately designed so they can’t be knocked accidentally.

Geoffrey Dell, an air safety specialist who has conducted numerous aircraft accident investigations, finds it hard to see how both switches could have been flipped in error.

“It’s at least a two-action process for each one,” he told CNN. “You’ve got to pull the switch out towards you and then push it down. It’s not the sort of thing you can do inadvertently.”

According to Dell, it would be “bizarre” for a pilot to deliberately cut fuel to both engines immediately after take-off.

There is “no scenario on the planet where you’d do that immediately after lift-off,” he said.

Pointing to the fact that both engine switches were flipped within a second of each other, Dell noted: “That’s the sort of thing you do when you park the airplane at the end of the flight… You plug into the terminal and shut the engines down.”

One possibility the report raises relates to an information bulletin issued by the US Federal Aviation Administration in 2018 about “the potential disengagement of the fuel control switch locking feature.” But, given that this was not considered an unsafe condition, Air India did not carry out inspections.

Dell said an aircraft’s flight data recorder should help explain how the fuel switches were flipped in each case. However, India’s AAIB has not released a full transcript of the conversation between the two pilots. Without it, Dell says it’s difficult to understand what happened.

Rescue workers at the site where the Air India plane crashed. Amit Dave/Reuters

Former pilot Ehsan Khalid also believes that the report’s findings raised questions over the position of the vital engine fuel switches, which, he said, should be clarified by the investigators.

Speaking to Reuters, Khalid warned against pinning the blame on the pilots. “The AAIB report to me is only conclusive to say that the accident happened because both engines lost power.”

He added: “The pilots were aware that the aircraft engine power has been lost, and pilots also were aware that they did not do any action to cause this.”

A full report is not due for months and India’s Civil Aviation Minister, Ram Mohan Naidu, said: “Let’s not jump to any conclusions at this stage.”

The Air India jet took off from Ahmedabad’s Sardar Vallabhbhai Patel International Airport in India’s western state of Gujarat on June 12, bound for London Gatwick.

Air India had said 242 passengers and crew members were on board. That included 169 Indian nationals, 53 Britons, seven Portuguese and one Canadian. Everyone on board was killed, except for one passenger.

The 19 people on the ground were killed when the plane crashed into the BJ Medical College and Hospital hostel.

Air India has acknowledged that it has received the report and said it will continue cooperating with authorities in the investigation.