Why cockpit audio deepens the mystery of Air India crash

Investigators have made a chilling discovery in the preliminary investigation into the Air India Flight 171 crash which killed 260 people in June.

Just seconds after take-off, both of the 12-year-old Boeing 787 Dreamliners fuel-control switches abruptly moved to the "cut-off" position, starving the engines of fuel and triggering total power loss. Switching to "cut-off" is a move typically done only after landing.

The cockpit voice recording captures one pilot asking the other why he "did the cut-off", to which the person replies that he didnt. The recording doesnt clarify who said what. At the time of take-off, the co-pilot was flying the aircraft while the captain was monitoring.

The switches were returned to their normal inflight position, triggering automatic engine relight. At the time of the crash, one engine was regaining thrust while the other had relit but had not yet recovered power.

Air India Flight 171 was airborne for less than a minute before crashing into a crowded neighbourhood in the western Indian city of Ahmedabad, marking one of Indias most baffling aviation disasters.

Investigators are probing the wreckage and cockpit recorders to understand what went wrong just after take-off. The Air India flight climbed to 625 feet in clear weather before losing location data about 50 seconds in, according to the FlightRadar24 website.

The preliminary report from the investigation - led by Indian authorities with experts from Boeing, General Electric, Air India, Indian regulators, and participants from the US and UK - raises several questions.

Investigators say the lever-lock fuel switches are designed to prevent accidental activation - they must be pulled up to unlock before flipping, a safety feature dating back to the 1950s. Built to exacting standards, theyre highly reliable. Protective guard brackets further shield them from accidental bumps.

"It would be almost impossible to pull both switches with a single movement of one hand, and this makes accidental deployment unlikely," a Canada-based air accidents investigator, who wanted to remain unnamed, told the BBC.

Thats what makes the Air India case stand out.

If one of the pilots was responsible for shutting down the switches, intentionally or not, it "does beg the question: why", said Shawn Pruchnicki, a former airline accident investigator and aviation expert at Ohio State University.

"Was it intentional, or the result of confusion? That seems unlikely, as the pilots reported nothing unusual.

"In many cockpit emergencies, pilots may press the wrong buttons or make incorrect selections - but there was no indication of such a situation here, nor any discussion suggesting that the fuel switches were selected by mistake," he said.

"This kind of error doesnt typically happen without some evident issue."

Peter Goelz, a former managing director of the USs NTSB, said: "The finding is very disturbing - that a pilot has shut off the fuel switch within seconds of flying."

"Theres likely much more on the cockpit voice recorder than whats been shared. A lone remark like why did you cut off the switches isnt enough," he said.

"The new details suggest someone in the cockpit shut those valves. The question is, who, and why? Both switches were turned off and then restarted within seconds.

"The voice recorder will reveal more: was the flying pilot trying to restart the engines, or the monitoring one?"

Investigators believe the cockpit voice recorder - with audio from pilot mics, radio calls and ambient cockpit sounds - holds the key to this puzzle.

"They havent identified the voices yet, which is crucial. Typically, when the voice recorder is reviewed, people familiar with the pilots are present to help match voices. As of now, we still dont know which pilot turned the switches off and back on," said Mr Goelz.

In short, investigators say whats needed is clear voice identification, a full cockpit transcript with labelled speakers, and a thorough review of all communications from the moment the plane was pushed back from the gate to the time it crashed.

They also say this underscores the need for cockpit video recorders, as recommended by the NTSB. An over-the-shoulder view would show whose hand was on the cut-off switch.

Before boarding Flight 171, both pilots and crew had passed breathalyser tests and had been cleared fit to fly, the report says. The pilots, based in Mumbai, had arrived in Ahmedabad the day before the flight and had adequate rest.

But investigators are also zeroing in on what they describe is an interesting point in the report.

It says in December 2018, the US Federal Aviation Administration issued a Special Airworthiness Information Bulletin (SAIB) highlighting that some Boeing 737 fuel control switches were installed with the locking feature disengaged.

While the issue was noted, it wasnt deemed an unsafe condition requiring an Airworthiness Directive (AD) - a legally enforceable regulation to correct unsafe conditions in a product.

The same switch design is used in Boeing 787-8 aircraft, including Air Indias VT-ANB which crashed. As the SAIB was advisory, Air India did not perform the recommended inspections.

Mr Pruchnicki said hes wondering whether there was a problem with the fuel control switches.

"What does this [bit in the report] exactly mean? Does it mean that with a single flip, that switch could shut the engine off and cut the fuel supply? When the locking feature is disengaged, what exactly happens? Could the switch just flip itself to off and shut down the engine? If thats the case, its a really serious issue. If not, that also needs to be explained," he said.

Others, however, arent convinced this is a key issue.

"I havent heard of this which appears to be a low-profile FAA issuance. Nor have I heard any complaints [about the fuel switches] from pilots - who are usually quick to speak up. Its worth examining since its mentioned, but it may just be a distraction," said Mr Goelz.

Capt Kishore Chinta, a former investigator with Indias Aircraft Accident Investigation Bureau (AAIB), wonders whether the switches tripped because of a problem with the planes electronic control unit.

"Can the fuel cut-off switches be triggered electronically by the planes electronic control unit without movement by the pilot? If the fuel cut-off switches tripped electronically, then its a cause for concern," he told the BBC.

The report says fuel samples from the refuelling tanks were "satisfactory". Experts had earlier suggested fuel contamination as a possible cause of the dual engine failure. Notably, no advisory has been issued for the Boeing 787 or its GE GEnx-1B engines, with mechanical failure ruled out for now pending further investigation.

It also said that the aircrafts Ram Air Turbine (RAT) had deployed - a clear sign of a major systems failure - and the landing gear was found in "down position" or not retracted.

The RAT, a small propeller that extends from the underside of the Boeing 787 Dreamliner, acts as an emergency backup generator. It automatically deploys in flight when both engines lose power or if all three hydraulic systems register critically low pressure, supplying limited power to keep essential flight systems operational.

"The deployment of the Ram Air Turbine (RAT) strongly supports the conclusion that both engines had failed," Mr Pruchnicki said.

A Boeing 787 pilot explained why he thought the landing gear was not retracted.

"These days, every time I take off in a 787, I notice the landing gear retraction process closely. By the time the gear handle is pulled, were already at about 200ft (60.9m), and the entire gear retraction process completes by around 400ft - roughly eight seconds in total, thanks to the aircrafts high-pressure hydraulic system."

The pilot believes the one flying had no time to think.

"When both engines fail and the aircraft starts going down, the reaction goes beyond just being startled - you go numb. In that moment, landing gear isnt your focus. Your mind is on one thing: the flight path. Where can I put this aircraft down safely? And in this case, there simply wasnt enough altitude to work with."

Investigators say the crew tried to recover, but it happened too fast.

"The engines were switched off and then back on. The pilots realised the engines were losing thrust - likely restarting the left one first, followed by the right," said Mr Pruchnicki.

"But the right engine didnt have enough time to spool back up, and the thrust was insufficient. Both were eventually set to "run", but with the left shut down first and the right too late to recover, it was simply too little, too late."

Families and friends of the crash victims had been anxiously awaiting the findings of the preliminary report.

When the report was finally released early on Saturday in India, Imtiyaz Ali, who lost his brother, sister-in-law, and their two young children - read it carefully, only to be disappointed by what he said "reads like a product description".

"Other than the pilots final conversation, theres nothing in it that really points to what caused the crash."

He said he hoped more details would be made public in the months to come.

"This matters to us. We want to know exactly what happened. It wont change anything for us now, we continue grieving - just as we have since that day.

"But at least well have some answers," Ali said.