As investigators scramble to understand what brought down Air India Flight 171, experts believe testimony from the sole survivor of the crash offers a vital clue.

Vishwash Kumar Ramesh, 40, who miraculously walked away from the Ahmedabad disaster, in which more than 240 people were killed, described flickering green and white cabin lights before the jet plunged to the ground.

Experts told The Telegraph that could indicate a loss of power, suggesting a problem with the plane’s engines, which ultimately generate the electricity it uses.

Speaking to reporters from his hospital bed, Mr Ramesh, 40, said: “When the flight took off, within five to 10 seconds it felt like it was stuck in the air.

“Suddenly, the lights started flickering green and white. The aircraft wasn’t gaining altitude and was just gliding before it suddenly slammed into a building and exploded.”

David Learmount, the consulting editor on safety at FlightGlobal and a former RAF pilot, said the flickering lights indicated that the generators that make electricity from the engines were not working properly.

Dr Guy Gratton, an associate professor of aviation and the environment at Cranfield University, also said they “might indicate that the power systems were switching from primary to backups”.

A loss of electrical power would probably have been caused by engine failure rather than the other way around, Mr Learmount said, because “once the engines are burning they don’t need electricity”.