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The engines on Air India flight 171 briefly cut off seconds after take-off, a preliminary report into the jet’s fatal crash last month has found.
India’s Air Accident Investigation Bureau said in its report released early on Saturday that the aircraft reached the necessary speed to lift off, but that seconds later, switches that control the flow of fuel to the jet’s two engines “transitioned” from “run” to “cut-off” position.
In the cockpit voice recording, one of the pilots is heard asking the other “why did you cut off?” to which he responded “that he did not do so”, the report said.
Although the two switches transitioned back to the “run” position between 10 and 14 seconds later, the engines had been starved of fuel and lost thrust, leading one pilot to declare “mayday, mayday, mayday”.
Aviation experts have said it is difficult for pilots to inadvertently move the fuel switches.
The crash on June 12 occurred moments after the Boeing Dreamliner 787-8 took off from Ahmedabad, bound for London Gatwick airport. The accident killed 241 people on board and another 29 on the ground, where the Boeing Dreamliner 787-8 crashed into a medical college near the airport.
It was India’s worst aviation disaster in almost three decades and the industry’s deadliest in 11 years, as well as the first fatal crash involving a Boeing Dreamliner.
The investigation was conducted with assistance from UK’s Air Accident Investigation Branch and the US National Transportation Safety Board.
The AAIB said that at this stage of its investigation there were “no recommended actions” to Boeing, the aircraft manufacturer, or GE Aerospace, whose engines powered the plane.
In a statement, Air India said that it “stands in solidarity with the families and those affected” and “[continues] to mourn the loss” of those killed in the accident.
It added that it was “working closely with stakeholders, including regulators” and continuing “to fully co-operate with the AAIB and other authorities as their investigation progresses”.
Boeing said: “Our thoughts remain with the loved ones of the passengers and crew on board Air India Flight 171, as well as everyone affected on the ground in Ahmedabad. We continue to support the investigation and our customers.”
GE Aerospace did not immediately respond to a request for comment. Indian conglomerate Tata Group, which owns the airline, referred reporters to the statement from Air India.
The preliminary findings, which are based on data drawn from the cockpit voice and digital flight data recorders as well as evidence gathered from the crash site, did not draw any final conclusions about what led to the switches being turned off.
Mark Martin of Martin Consulting, an aviation safety firm based in Gurugram India, said the AAIB and other investigators needed to probe further how the fuel switch had been cut off. He also questioned why the accident report made no reference to cockpit camera footage.
“No pilot would be foolish enough to cut fuel to both engines during a phase when he needs engine power the most,” said Martin. “It is imperative that we wait for the entire, comprehensive investigation report.”
Sumeet Sabharwal, the captain, had more than 11,500 hours of flying experience, while first officer Clive Kunder had more than 3,400 hours. The report said both pilots had an “adequate rest period” and took breathalysers before the flight.
The report also referenced a 2018 airworthiness bulletin by the US Federal Aviation Administration regarding said fuel switches that had been installed on Boeing 737s, a smaller model “with the locking feature disengaged”.
The locking feature prevents “inadvertent” movement between the fuel supply and cut-off positions, the notice said. If it was disengaged, it “could result in an unintended consequence, such as an in-flight engine shutdown”. It said the locking mechanism was similar on various Boeing aeroplane models, including certain 787s.
But the report added that the issue was not considered an “unsafe condition” by the FAA and that Air India did not inspect its planes’ fuel switches because the bulletin’s recommendations were only advisory and not mandatory. It added that the mechanism in the plane was replaced in 2019 and 2023 for reasons “not linked to the fuel control switch”.
The report also noted that closed-circuit television footage from the airport showed the jet’s ram air turbine, a device that can provide emergency power for events such as electrical or engine failure, had been deployed. The jet had already begun to lose altitude before it crossed the airport boundary.
It also said there was “no significant bird activity” in the vicinity of the flight path.
The Dreamliner, a wide-body 787 used for long-haul flights, is Boeing’s most advanced model and includes lightweight composite materials that aid fuel efficiency. The company has delivered more than 1,100 of the best-selling aircraft to airline customers.
The accident has shocked Indians at a time of rapid expansion of air travel in the world’s most populous country. It has also presented Air India’s owner Tata Group with its biggest crisis since bought the airline from state ownership, seeking to revive the brand once seen as a national embarrassment.