AIR India crash investigators believe an emergency power system kicked in – raising questions about whether the engines were working properly.

A raft of analysts now agree that a small turbine generator deployed as the Boeing 787 went down, after a “game-changer” video emerged.

Days after the catastrophe which killed more than 270 people, a HD video surfaced showing a “protrusion on the belly of the aircraft” with a “little grey dot” beneath it.

Commentators say this was a system called Ram Air Turbine (RAT) poking out from the fuselage of the plane, which failed to climb more than 450ft.

Commercial airline pilot Steve Schreiber, known as Captain Steve, explained: “Many aeroplanes have it. It is just behind the wing on the right side of the aeroplane, there is a little door that holds it in.

“It looks like a little Evinrude motor, it’s a little two bladed prop.

“The purpose is to provide electrical and hydraulic pressure for the aircraft on an extreme emergency.”

Steve explained there are three things which could cause the RAT to deploy on a 787: “A massive electrical failure, a massive hydraulic failure, or a dual engine failure.

“But I think the fact the aeroplane is mushing out the sky gives the idea it was a dual engine failure,” he said.

Other analysts agree that the RAT system deployed, and that the most likely cause was duel-engine failure.

Anthony Brickhouse, a US-based aerospace safety consultant, told the Wall Street Journal that the most common reason the propeller comes out is because the pilot thinks both engines have failed.

However, he reiterated this is highly unusual, telling the paper: “In commercial aviation, a dual engine failure is extremely rare.

“Our engines today are more efficient and reliable than ever.”

While there is growing consensus over the RAT deployment, investigators haven’t confirmed whether engine, hydraulic or other problems triggered the emergency system.

And it may be some time before we get an official diagnosis.

India’s Ministry of Civil Aviation said the accident remains under investigation and that more information would be provided in due course.

Air-accident investigations can take more than a year – and even then will often point to a number of contributing factors.

Meanwhile, both of the black boxes have now been recovered.

One records flight data, such as altitude and speed, whilst the other monitors the cockpit sound.

The first was recovered from a rooftop near where the plane came down just 28 hours after the crash.

And the second is expected to reveal the pilots’ panic as the plane went down.

We already know that the pilot, Captain Sumeet Sabharwal, made a desperate mayday call to air traffic control in the moments before the disaster.

He cried out: “‘Thrust not achieved […] falling […] Mayday! Mayday! Mayday!”

The two pilots then wrestled for 17 seconds with the controls as the jet sank through the air before careening into the buildings below.

Sabharwal had 22 years of experience and had racked up 8,200 in the air.

The plane gained just a few hundred feet of altitude when the power apparently cut out, killing more Brits than any air disaster since 9/11.

Despite more than 270 people dying in the catastrophe, the pilot has been credited with saving “dozens of lives”.

Sabharwal diverted the jet at the last second to avoid slamming into a three-storey apartment building, according to locals on the ground.

All 18 families in the three-storey building under the flight path are convinced they owe their lives to Captain Sumeet Sabharwal.

He managed to divert the plane towards a patch of grassland.

The locals raced from their homes in Ahmedabad when a fireball from 90 tons of aviation fuel ignited as the plane slammed into the ground.

The aircraft obliterated the top two floors of a disused four-storey military building.

But the fire tore through the college’s hostel, killing dozens of students and staff who were having lunch in the canteen.