Fuel control switches to the engines of an Air India flight that crashed shortly after takeoff, killing 260 people, were moved from the "run" to the "cutoff" position moments before impact, a preliminary investigation report said.
The report, issued by India's Aircraft Accident Investigation Bureau, did not offer any conclusions or apportion blame for the 12 June, but indicated that one pilot asked the other why he cut off fuel, and the second pilot responded that he had not.
The Boeing 787-8 Dreamliner was headed from Ahmedabad in western India to London when it crashed, killing all but one of the 242 people on board as well as 19 people on the ground.
In its 15-page report, the investigation bureau said that once the aircraft achieved its top recorded speed, "the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 1 sec".
"In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff. The other pilot responded that he did not do so," it said.
The aircraft quickly began to lose altitude.
The switches then returned to the RUN position and the engines appeared to be gathering power, but "one of the pilots transmitted 'MAYDAY MAYDAY MAYDAY'", the report said.
Air traffic controllers asked the pilots what was wrong, but then saw the plane crashing and called emergency personnel to the scene.
The report did not identify which remarks were made by the flight's captain and which by the first officer, nor which pilot transmitted the Mayday signal.
At the crash site, both fuel switches were found in the run position and the report said there had been indications of both engines relighting before the low-altitude crash.
Both pilots were experienced jet pilots with about 19,000 total flying hours between them, including more than 9,000 on the 787.
The preliminary report also does not say how the switch could have flipped to the cutoff position on flight.
US aviation safety expert Anthony Brickhouse said a key question is why were the switches moved in a way that is inconsistent with normal operations.
"Did they move on their own or did they move because of the pilots?" he asked. "And if they were moved because of a pilot, why?"
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.
The bureau said there were "no recommended actions to B787-8 and/or GE GEnx-1B engine operators and manufacturers", suggesting no technical issues with the engines (GE) or the aircraft (Boeing).
The bureau said the investigation was ongoing, and that additional evidence and information has been "sought from the stakeholders".
The plane was carrying 230 passengers — 169 Indians, 53 British, seven Portuguese and a Canadian — along with 12 crew members.
Dozens of people on the ground were injured.
One passenger miraculously survived, a British citizen who was seen walking out of the wreckage of the crash, and who has since been discharged from hospital.
