Speculation is growing about the cause of the Air India plane crash last month after a report suggested the pilot deliberately cut off the fuel.

A cockpit voice recording suggests that the captain, Sumeet Sabharwal, shut off the fuel supply to the aircraft’s engines, The Wall Street Journal reported on Wednesday.

The first officer questioned the captain about switching the fuel controls to the “cut-off” position moments after take-off, according to the report. The captain denied he had turned the switches.

The newspaper cited sources familiar with the preliminary assessment by US officials investigating the crash on 12 June in Ahmedabad, western India, which killed 260 people, including 53 British nationals.

The London Gatwick-bound Boeing 787 Dreamliner crashed into a medical college moments after take-off. One person on board survived.

The back of Air India flight 171 after it crashed into a medical college moments after take-off (Photo: Sam Panthaky/AFP)

On Thursday, India’s air accident authority warned against speculation following the Journal‘s report, as media attention focuses on a possible murder-suicide motive.

Indian pilots’ unions have defended the crew from accusations that one of the pilots caused the crash, either deliberately or accidentally.

Officials from Boeing and Air India did not immediately respond to requests for comment on the report’s findings.

How do the 787’s fuel switches work?

A preliminary report released on Saturday by India’s Aircraft Accident Investigation Bureau (AAIB) found that the fuel switches had moved from “run” to “cut-off” just one second apart shortly after take-off. However, it did not clarify how the switches were turned, and did not attribute fault.

Details about what happened in the cockpit remain unclear as the investigation continues, but experts note that, mechanically, the switches are typically operated manually by one of the pilots.

“In the centre, between the two pilots, is a large console. All sorts of systems are on there, but the main bit in the middle, are the aircraft throttles, the accelerators, if you like,” said Paul Firth, consultant for Astral Aviation and current Boeing 787 pilot with over 30 years of experience in military and civil aviation.

“There are two levers, which you push forward to make the aircraft go faster, or you pull backwards to make the aircraft slow down, they control the fuel flow to the engines. Directly beneath those two are the two switches which everyone is talking about. They are called the fuel control switches.”

The switches can be in two positions – cut off, which means no fuel will run to an engine, and run, which means fuel is allowed to flow to the engine.

The Air India Boeing 787-8 Dreamliner crashed moments after taking off from Sardar Vallabhbhai Patel International Airport (Photo: Amit Dave/Reuters)

Before take-off, when the pilots start the engines, those two switches are moved from cut off to run. It takes about 30 to 40 seconds for the engines to be fully operational, Firth said.

“Once they’re running, we would not normally touch those switches again until the end of the flight, when we’re back at the terminal, or the destination,” he added.

“You can switch them off at any time – they are not locked once the aircraft is airborne. There is a mechanism around them, which is to prevent you accidentally switching them off, and that is that you have to lift each switch up and out, if you like, towards yourself. Before it will then move down into the cut-off position.”

Were the fuel switches deliberately cut off?

Firth emphasised that it was highly unlikely the switches could be cut off by accident.

“There’s a little collar which has to be gotten over, so you couldn’t for example, accidentally put your hand out and knock the switch from run to cut off. It is a controlled motion, and it has to be deliberately done.”

He said the engine controls for all commercial airline engines were very similar in design: “An aircraft designer is not for one moment going to imagine that somebody is going to do that, deliberately, at the wrong time.”

Relatives mourn at the coffins of victims of the Air India crash in Ahmedabad, India (Photo: Dibyangshu Sarkar/ AFP)

According to the Wall Street Journal, the first officer, Clive Kunder, 35, had the controls of the plane during take-off, and asked Captain Sabharwal, 56, why he had turned off the fuel switches. Sabharwal replied that he had not.

The WSJ quotes US officials’ early assessment of evidence as saying that Kunder had panicked while the captain remained calm. The sources cited did not clarify whether they believed the action was deliberate or accidental.

However, the WSJ reported that US officials believed criminal investigators should be involved in looking into the incident.

No direct transcript of the recorded discussion has yet been published.

On Thursday, an official from Air India said that “inspections have been completed and no issues were found” with the fuel switches on its other Boeing planes.

While it is still unclear how the switches were turned off, experts note that —aside from being operated intentionally — investigators may be looking into a scenario where certain actions could have been taken unintentionally.

A family member places a garland on a photograph of Akash Patni, who died in the disaster. An investigation is under way to determine what caused the crash (Photo: Amit Dave/Reuters)

“We have a lot of training in the airline aviation industry and we try to correct for things we call action slips. So if I ask you, for example, to put the kettle on, maybe for a cup of tea, but you, without thinking, switch the oven on, okay, you’ve responded to a request from me, but… you were thinking about something else and you’ve done something else entirely,” said Firth.

However, if this were a case of an action slip, the pilot should also have been following the rest of the steps, such as bringing the landing gear and wheels up. “They were down the whole time, that’s normally the first thing you do,” Firth said.

Could the disaster have been prevented?

Dr Jason Knight, a senior lecturer in fluid mechanics at the University of Portsmouth, said when the switches were turned off, the fuel stops flowing into the engines right away: “They’re designed in case of an engine fire or some other problem with the engine, so the fuel would be cut off fairly quickly.”

As soon as the fuel is cut off, the engine will be losing power and the spools will start to slow down, he added, pointing out that this matched how the plane had appeared before crashing. If one of the engines was operational, the aircraft would have continued its flight.

“It’s very strange that the pilot would have activated those switches,” Dr Knight said. “I mean, they would only do it if the engines were on fire or if there was some technical problem, the engine wasn’t sounding right or something was wrong.

“They’d want to turn the fuel off immediately to save the plane. But there wasn’t any of that at all. The engines were working perfectly fine from what I can gather.”

Dr Knight pointed out that there still could possibly have been some type of technical or electrical malfunction affecting the switches, but a lot remained unclear.

He added: “So if the pilot did actually switch it off, it’s very strange that he did.”

Investigators will be able to recover the switching mechanism from the crash site and draw conclusions based on what they find, Dr Knight said.

If the pilots had detected a possible technical issue earlier, they could have aborted the take-off, but the incident happened at a time when the plane was already in the air at a very low altitude.

“It couldn’t have happened at a worse time,” Dr Knight said. “With this one, it is very puzzling as to what has happened.”