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Seconds after takeoff and moments before an Air India flight crashed last month, the fuel was cut off to both engines of the plane, investigators said early on Saturday, in a preliminary assessment of information from the Boeing 787’s voice and data recorders.
The narrowed focus on the fuel switches on Air India Flight 171 raised questions about the pilots’ actions and appeared to rule out mechanical failure or design flaws. The report said “there are no recommended actions” to the aircraft and engine manufacturers, Boeing and General Electric.
“In the cockpit voice recording, one of the pilots is heard asking the other why did he cut off” the fuel, said the report, by India’s Aircraft Accident Investigation Bureau. “The other pilot responded that he did not do so.”
The London-bound plane went down on June 12, about 30 seconds after takeoff from Sardar Vallabhbhai Patel International Airport in the western Indian city of Ahmedabad. All but one of the 242 people aboard were killed.
The plane rammed into the dining hall of a medical college before exploding in flames. Altogether, more than 270 people were killed, including dozens on the ground, officials said. It was India’s worst aviation disaster since 1996.
The supply of fuel to the engine is controlled by two switches in the flight deck. Starting about 10 seconds after the fuel was cut off on Flight 171, the data recorder shows, the switches were moved to turn the fuel back on. But the plane could not gain power quickly enough to stop its descent.
Each switch is equipped with a locking mechanism that is supposed to prevent accidental movement, experts said. To turn the fuel supply on, the switch must be pulled outward and then moved to a “RUN” position, where it is released and settles back into a locked position. To turn the fuel supply off, the switch must be pulled outward again, moved to the “CUTOFF” position and then released again.
According to the report, the fuel control switches were turned off “one after another” about a second apart, and “the aircraft started to lose altitude before crossing the airport perimeter wall.”
Safety experts said it appeared unlikely that the switches were moved without human involvement, whether intentional or accidental.
The fuel switches have safeguards built around them to avoid any accidental switching off, said Shawn Pruchnicki, a former airline accident investigator and aviation expert at Ohio State University.
“For example, on the 787 and probably more airliners these days, the switches themselves — you can’t shut them off without actually lifting them up,” he said. “So there’s a little mechanical gate built into the switch — you have to lift it up over this little gate. So you can’t just bump it.”
The flight’s captain was Sumeet Sabharwal, who had over 15,000 hours of flying experience, while First Officer Clive Kunder brought 3,400 hours of flying experience, Air India said. That is more experience than officials attributed to the pilots last month, when they estimated a combined experience of about 10,000 hours.
India’s Aircraft Accident Investigation Bureau, the U.S. National Transportation Safety Board and Boeing have been trying to determine what caused Flight 171 to crash. The cockpit voice recorder and the flight data recorder, usually referred to as the black boxes, were recovered from the debris.
Although there was initial concern that the devices might have been damaged in the extreme heat of the fire, investigating teams managed to retrieve data from the boxes.
Video filmed by residents in nearby homes, as well as CCTV footage, show the plane struggling to gain lift immediately after taking off. A New York Times analysis of photos and videos suggested that the plane might have experienced a catastrophic loss of hydraulic, electrical or engine power.
It could take months, possibly years, to reach definitive conclusions. But as a member of the International Civil Aviation Organization, India was obliged to submit a preliminary investigative report within 30 days of the crash.
The preliminary report was inconclusive, and said the investigators will continue to “review and examine” further evidence.
It appeared to rule out one theory floated by experts, of fuel contamination. The report said a “very limited amount of fuel” could be retrieved from the aircraft, which exploded into flames, and tests on those samples would continue. But lab tests on samples taken from “the bowsers and tanks used to refuel the aircraft” had found the fuel “satisfactory.”
The report not recommending any action to the aircraft and engine manufacturers, three weeks after data was decoded, was seen by experts as an indication of no obvious sign of mechanical failure or design flaws. That would have prompted urgent communication to manufacturers to check other aircraft.
The report, however, noted that the Federal Aviation Administration had issued a bulletin in 2018 recommending that airlines inspect the switches on the 787 and other jets amid reports that some may have been installed with the locking mechanism disengaged.
But the F.A.A. did not rule that to be an unsafe condition at the time, the report said. The switches on the Air India plane were replaced by 2023, with no defects reported since. And, by that time, the manufacturer would have almost certainly inspected the part to ensure the locking mechanism was engaged, said John Cox, a former airline pilot and chief executive of Safety Operating Systems, a consulting firm.
In a statement, Air India said it had received the preliminary report but could not comment on “specific details” mentioned “given the active nature of the investigation.”
The crash brought scrutiny not only to Boeing, but also to Air India, the country’s oldest carrier, which was acquired by Tata Group after half a century as a state-owned enterprise. The crash occurred just as Air India was trying to pitch itself as a modernizing carrier.
The airline’s last major crash was in 2020, when a passenger plane operated by Air India Express, a subsidiary, skidded and cracked in two on a rain-soaked runway, killing at least 17 people in the southern Indian state of Kerala. In 2010, an Air India Express plane overshot a hilltop runway in Mangalore, in the western state of Karnataka, killing more than 150 people.
Article source: nytimes.com