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?.

In his final message to air traffic controllers, the plane?s pilot said the Boeing 787-8 Dreamliner had ?no thrust?, was ?losing power? and was ?unable to lift?. The Dreamliner is designed to be able to climb and fly safely in the event of having only one engine operational.

Speculation has been rife over what may have caused the crash, including the possibility of pilot error, faulty flaps, electrical problems or engine failure.

A bird strike is a prominent hypothesis, and could have caused a catastrophic engine failure leading to such a situation, but there has been no evidence of flocks in the area at the time of the crash.

?More than one thing went wrong here. The thing that might have started it, and I think probably did, was a loss of power,? said Mr Learmount.

?Whether it was loss of power on one engine or both engines is not clear. But the failure of a single engine should not cause a crew to lose control of a modern airliner, even in the critical early climb phase.

?At the same time, simultaneous engine failures for unconnected reasons simply do not happen, based on the entire history of aviation. So if there was a failure of both, the question is what could have caused it.?

The two engines on the plane are made by General Electric aviation and have a good safety history. On Friday, the Indian aviation regulator, the Directorate General of Civil Aviation issued a notice to Air India to conduct more inspections of all of its 787-8 and 787-9 fleet with GE engines.

This includes an inspection of the fuel monitoring systems, a test of the electronic engine control, a check of the hydraulics and a review of take-off parameters. ?Power assurance checks? are also to be done on each plane within two weeks

Dr Akhil Bhardwaj, a senior lecturer in aviation safety at the University of Bath, told The Telegraph he believed the DGCA was acting with an ?understandable abundance of caution?

Last year, a United Airlines 787 jet, which has the same GEnx-1B engines as the doomed AI 171 flight, suffered an ?uncontained left engine failure shortly after take-off? while flying from Singapore to San Francisco last year, according to a National Transportation Safety Board report.

The engine ceased working at cruise altitude and set alight, according to the report, with the pilots managing to circle back and land the plane back in Singapore using just one engine.

A GE Aerospace spokesman said: ?Safety is our top priority, and we support the action being taken by the Indian Directorate General of Civil Aviation for enhanced safety inspections of the Air India 787-8/9 fleet.

?We continue to work closely with the appropriate regulatory and investigative agencies, and we are committed to providing all technical support necessary to understand the cause of this accident.?

Experts have suggested that the Dreamliner, which until Thursday had an unblemished safety record, also deployed its Ram Air Turbine (RAT) during the ill-fated 60 seconds between take-off and the crash.

The RAT is a propeller-like device that sits in the fuselage between the wings and is only deployed in the most dangerous situations, to provide emergency power to vital electrical systems.

Sambulo Matema, a lecturer in aviation management at University College Birmingham, told The Telegraph: ?There is credence to this theory.

?In a complete power?loss scenario, the aircraft transitions from engine?supplied power to RAT power, and lighting anomalies can occur.

?This behaviour aligns with established emergency procedures and the expected performance of aircraft electrical systems under severe duress.

?After total power loss, the RAT deploys as a fallback power source. During this transition, green emergency lighting activates, and white lights may flash while onboard systems reboot and stabilise.?

Mr Learmount, who flew Hercules military transport planes around the Middle East during his RAF career, said the RAT would have sent power to the cockpit. The plane?s batteries would also have supported vital systems.

However, neither could have done anything to keep the plane aloft in the event of its turbines spooling down.

All this suggests the fault lay in the engines. However, what could have caused them to shut down remains unclear.

One theory is contaminated fuel. In 2010, a Cathay Pacific flight to Hong Kong almost ended in disaster when the pilot was unable to control engine thrust, leading it to land at twice the usual speed.

It later emerged that fuel pumped into the plane had been contaminated with saltwater, damaging its engines over time. However, such problems are rare.

Mr Learmount said: ?If you go looking for a potential cause of multiple engine failure, fuel contamination could do it. But again, history is against that potential cause in observed reality. The same engineering or maintenance error could also have been made with both engines.?

He cited the example of engineers failing to replace vital seals after topping up the engines of a Lockheed Tristar with oil in the 1980s, leading to a near tragedy.

He said: ?I think that at the basis of all this they lost power, all of it, part of it, one engine, both engines. If they had been charging along the runway and they felt there was something wrong with the engines, they?d have stopped. So they did not have any doubts about their ability to get airborne and stay there. Everything started going pear-shaped very soon after take-off.

?When you look at that aeroplane going in, it went in serenely to its death. It was essentially under control, but the pilots could not get enough power to climb.?

Mr Learmount said it was also possible that the crew experienced some form of technical limitation on their ability to lift the nose of the plane, which they could have described as a loss of thrust in the heat of the moment.

While that was what happened in the case of the two fatal 737 Max crashes in 2019 and 2020, when new software overrode pilot inputs, that system was entirely unique to the narrow body model.

?There is virtually no commonality in the way the 737-series controls work and the manner in which the 787 operates,? he added. (THE TELEGRAPH)

Update news