Someone switched off the fuel to Air India's engines

“In the cockpit voice recording, one of the pilots is heard asking the other why did he cut off” the fuel. “The other pilot responded that he did not do so.” 

Each switch is equipped with a locking mechanism that is supposed to prevent accidental movement, experts said. 

The fuel control switches were turned off “one after another” about a second apart unlikely without human involvement, whether intentional or accidental. 

"Starting about 10 seconds after the fuel was cut off on Flight 171, the data recorder shows, the switches were moved to turn the fuel back on. But the plane could not gain power quickly enough to stop its descent."

GRTWT.