The engines on Air India flight 171 briefly cut off seconds after take-off, a preliminary report into the jet’s fatal June 12 crash has found.
India’s Air Accident Investigation Bureau said in its report 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”.
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.
Air India flight 171 crashed on June 12 seconds after take-off from Ahmedabad, bound for London Gatwick airport, in India’s worst aviation disaster in almost three decades and the industry’s deadliest in 11 years.
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.
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.
Aviation experts have said it is difficult for pilots to inadvertently move the fuel switches.
Closed-circuit television footage from the airport showed that 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 report said. The jet had already begun to lose altitude before it crossed the airport boundary.
Boeing and GE Aerospace did not immediately respond to a request for comment.
In a social media post, Air India said it would continue to work closely with AAIB and other authorities on the ongoing investigation. Indian conglomerate Tata Group, which owns the airline, referred reporters to the statement from Air India.
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” prior to operating the flight.
It also said there was “no significant bird activity” in the vicinity of the flight path.
The report mentioned a 2018 airworthiness bulletin by the US Federal Aviation Administration of “potential disengagement of the fuel control switch locking feature” on Boeing 737s, a smaller model.
The report said the locking mechanism was similar on various Boeing aeroplane models, including certain 787s. It added that Air India did not inspect its planes’ switches because the FAA advisory was not mandatory. It was not immediately clear if there was a link to the accident.
The crash was the first fatal accident involving a Dreamliner. The 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 UK’s Air Accident Investigation Branch and the US National Transportation Safety Board have assisted India’s AAIB with the investigation into the crash.
The accident is the biggest crisis in the three and a half years since Tata bought the airline from state ownership and sought to revive the brand many Indians once saw as a national embarrassment.