A preliminary report into last month's Air India plane crash in Ahmedabad found the aircraft engines' fuel control switches shifted from "run" to "cutoff" within a second of each other, causing a loss of thrust.
Only one person out of the 242 people on board the airplane survived, and at least 19 people died on the ground where the plane crashed moments after takeoff.
According to a preliminary report by the Aircraft Accident Investigation Bureau (AAIB) released on Friday, the plane reached 180 knots indicated airspeed (IAS), 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 Boeing 787 Dreamliner immediately began to lose thrust.
Questions about the pilots' actions
The report did not provide a reason for why the switch could have flipped to the cutoff position.
"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., suggesting no technical issues with the engines or the aircraft.
The bureau also explained that the Engine and Flight Data Recorder (EAFR) — more commonly known as the aircraft's "black box" — was "substantially damaged," to the extent that its data "could not be downloaded through conventional means."
In the cockpit voice recording retrieved from the black box, the report said "one of the pilots is heard asking the other why did he cutoff," and the other pilot "responded that he did not do so."
The Boeing 787 Dreamliner aircraft crashed into a medical college hostel shortly after takeoff from Ahmedabad en route to London's Gatwick Airport on June 12.
The plane burst into flames, with the report confirming that it "was destroyed due to impact with the buildings on the ground and subsequent fire." Five buildings on the ground were impacted, suffering major structural and fire damage.
How did the fuel switch get flipped?
US aviation safety expert John Cox told Reuters news agency that it would not be possible for a pilot to accidentally move the fuel switches. "You can't bump them and they move," he said.
Flipping the fuel switch from "run" to "cutoff" almost immediately cuts the engine.
It is mostly used to turn engines off after an aircraft has reached its gate and in certain emergency situations like an engine fire.
The report did not provide any information that an engine cutoff was required because of any emergency.
