Fuel to the engines of the Air India plane that crashed last month appears to have cut off shortly after take-off, a preliminary report has found.

According to the report by India's Aircraft Accident Investigation Bureau (AAIB), switches in the Boeing 787 Dreamliner's cockpit that controlled fuel moved to a "CUTOFF" position.

It said: "Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of one second.

"The Engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off."

There was then confusion in the cockpit. In the voice recording, one of the pilots is heard asking the other why he "cut off". The other pilot responds that he did not do so.

The 15-page report did not identify which comments were made by the flight's captain and which were made by the first officer. One of the pilots made a "mayday, mayday, mayday" call just before the crash.

Both pilots were experienced, with around 19,000 flying hours between them, including more than 9,000 on the 787.

Flipping to cutoff almost immediately cuts the engines, and is most often used to turn the engines off once a plane has arrived at its airport gate and in certain emergency situations, such as an engine fire - though both switches together are rarely used simultaneously.

The report does not indicate there was any emergency requiring an engine cutoff. It also does not give a conclusion as to how the switches moved.

Tim Atkinson, a pilot and aviation consultant, told Sky News' "there are very few situations or circumstances which would explain this".

He explained: "One would be an utterly extraordinary human error, an unintentional act, and the other - I'm very sorry to say - would be an intentional act. And that's not a suggestion or allegation, it's simply an analysis of the small amount of information that we have at hand at this moment."

One of the engines was able to be restarted, but could not reverse the plane's deceleration, the report found.

India's AAIB said in its report: "At this stage of investigation, there are no recommended actions to Boeing 787-8 and/or GE GEnx-1B engine operators and manufacturers."

No significant bird activity was observed in the vicinity of the plane's flight path, the report said. The aircraft started to lose altitude before crossing the airport perimeter wall, it added.

The plane plummeted into a busy area, and 19 others on the ground while incinerating everything around it.

The plane's two black boxes, which combined cockpit voice recorders and flight data recorders, were recovered in the days after the crash.

They provide vital data such as altitude, airspeed and final pilot conversations, which can help narrow down the possible causes behind a crash.

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The AAIB's report is based on the initial findings of the probe, marking 30 days since the crash. It said the investigation is continuing. A final report is expected within a year.