PILOTS manually cutting the engines were to blame for the two most deadly air crashes of this decade, investigations suggest.

With a total of 420 lives lost in the flick of three buttons, urgent questions are swirling about what can be done to reduce the risk of pilot error or sabotage.

The Jeju Air emergency-landing crash killed 179 people in December, and 241 people died when the Air India plane came down shortly after takeoff in June.

Investigators have sensationally revealed there is “clear evidence” that the Jeju Air pilots mistakenly shut down the wrong engine after a bird strike.

The plane was then forced to make an emergency landing at Muan International Airport on December 29, where it slammed into a concrete wall and burst into a fireball.

Meanwhile, the leading theory in the Air India crash is that the pilot manually flipped both guarded fuel switches to the “cut-off” position — a move aviation experts say could only have been deliberate.

A report from the Aircraft Accident Investigation Bureau of India (AAIB) revealed a recording of the panicked co-pilot asking which the main pilot shut off the engines.

Terry Tozer, former airline pilot and author of “Confessions of an Airline Pilot – Why Planes Crash”, told The Sun that it would have been be possible for the Air India pilot to shut off the engines without the other noticing.

In the cockpit were Captain Sumeet Sabharwal and First Officer Clive Kunder.

Terry said: “The handling pilot, which we know was the First Officer, would have had his hands full.

“He would have had his hands on the controls, but the monitoring pilot [Sumeet] would have his hands free.”

“There is absolutely no procedure or logical reason why you would shut the engines off just after takeoff. That’s so blindingly obvious that it doesn’t need to be stated.

“So either it happened by accident, which I think a lot of people find extremely hard to believe or it was done deliberately.”

Terry said that the switches are “latched”, meaning you have to lift them up before you can move them.

Despite the safety mechanism, Terry said it would “probably” have been possible for one pilot to shut down the engines without the monitoring pilot noticing, because the switches “would be kind of behind his natural line of sight”.

The experience pilot also called on investigators to release a key piece of evidence that could clear up what happened in India.

He explained the area microphone on the cockpit voice recorder would have picked up the sound of the switches being flicked.

Terry said: “So it would have been helpful if the investigators had said whether or not they were able to tell whether a switch type sound was detectable around about the time that they think the switches might have been switched off.”

Speaking about the Jeju crash, Terry said the pilots “obviously” shut down the wrong engine by “mistake” – but revealed they would have been contending with a chaos in the cockpit.

He said: “They probably would have had all kinds of bells and whistles going off and lots of indications that both engines were in trouble.”

The former pilot said “takes time to analyze whether or not you should shut down one or neither or both” – but this was time the Jeju pilots did not have.

He also said the new revelations about those crucial moments had been revealed in a “very odd manner”.

Terry said: “I understand that it was released to the relatives of the victims and in private, prior to release to the general public.

“And then that causes riots and chaos.”

However, Terry said that whatever happened in the two cockpits, there is one factor that determines passengers’ fate above all else.

He said the “single most important thing” in passenger safety is the “airline culture”.

Terry explained: “If it is a disciplined professional safety culture with a good training regime, then that makes a huge difference.”

Terry recalled a similar occasion when the wrong engine was shut down – the Kegworth air disaster of 1989 – and said that was “definitely a cultural problem in the training department”.

“That may have been a factor with Jeju Air,” he said.

In the wake of the two tragedies, many aviation figures have called for he introduction of cockpit CCTV.

That would clear up immediately how the two engines came to be shut off on the Air India flight – but Terry said pilots would push back.

He said: “I can see why the investigators might welcome cockpit CCTV.

“We should be doing everything we can to minimize crashes.

“And in any responsible environment, with a good airline and a regulatory environment that is already happening.

“And obviously, if there was a video evidence of what went on on the cockpit. They would know the answers pretty clearly by now.

“But it’s something that I think pilots would resist, for the simple reason that they’re already scrutinized, trained, checked, examined, monitored, regulated so much.”