Indian investigators probing the crash of Air India Flight 171 say both engines lost fuel shortly after takeoff, in a preliminary report documenting their findings on the country's worst plane crash in decades.
New details from India's Air Accident Investigation Bureau on the June 12 crash indicate that the switches controlling fuel for both engines went into the cutoff position early in the flight, causing the plane to lose thrust.
The switches were then returned to the operating position, a standard procedure for restarting the engines in mid-flight.
Cockpit audio suggests both pilots were confused about the switch configuration change. “In the cockpit voice recording, one pilot can be heard asking the other why he cut out,” the report’s authors write. “ The other pilot responded that he had not done so .”
The switches have protections designed to prevent them from being inadvertently moved.
“Each switch has a mechanical lock that allows it to be lifted and then moved, so it’s very unlikely that switches like this would be inadvertently moved absent some mechanical failure ,” said Jeff Guzzetti, former director of the Federal Aviation Administration’s Accident Investigation Division.
It is also unusual that both switches were inadvertently moved to the cutoff position “one right after the other, within a second of each other,” Guzzetti added. Guzzetti did not rule out the possibility that the switches were moved intentionally, citing the need to investigate the pilots as well.
The preliminary report was released at 1 a.m. local time on Saturday. The investigation is still in its early stages and is unlikely to be completed for another year.
The Boeing 787 took off from Ahmedabad Airport in western India before crashing into a medical college dormitory, causing a massive fireball. All but one of the 242 people on board died, as did 19 people on the ground. One passenger miraculously managed to escape the plane.
The plane was headed to London's Gatwick Airport. The plane appeared to be taxiing down the runway and taking off normally, according to experts who reviewed video footage from the scene. But after a few seconds in the air, the plane stopped climbing. The pilots transmitted a distress call 23 seconds after the first switch was turned off, according to the report.
The plane's landing gear remained down, and video and audio suggest that an emergency device known as a ram air turbine, or RAT, had been deployed on the plane, experts said, potentially indicating a rare double engine failure. The device drops from the underside of the plane and spins as it moves through the air to provide emergency power.
However, in the weeks since the crash, what ultimately caused the accident has remained unclear. Aviation news site The Air Current reported this week that investigators were focusing on the movement of the flight deck fuel switches, citing people familiar with the investigation. The switches are typically used to control fuel flow when starting and stopping the engine, but can also be used if an engine needs to be restarted in flight.
The findings released Friday are required by international standards governing accident investigations. But they are a summary of the facts available to investigators and do not include conclusions about the cause of the crash. Investigators are likely to take a year or more to complete their work. The U.S. National Transportation Safety Board is leading a team of Americans assisting in the investigation, but the responsibility for releasing information remains with Indian authorities.
The report's authors note that they make no recommendations to Boeing, the plane's manufacturer, or General Electric, the engine manufacturer.
Authorities typically regularly inform the public immediately after serious accidents, but in the case of the Air India crash, very little official information had been shared. This left a void that was sometimes filled with misinformation and fueled concerns among international safety experts that the lack of transparency would make it difficult for other airlines to know whether there were broader safety risks that needed to be urgently addressed.
The investigation got off to a slow start. The plane's black boxes, which record conversations between the pilots and data from the plane's systems, were recovered from the wreckage in the days following the crash. But investigators didn't begin analyzing the data until June 24 at a Delhi laboratory. The information contained in the boxes will be vital to investigators in determining what went wrong.
The crash was the first involving a 787, a fuel-efficient Boeing jetliner first put into service in 2011. The new planes were briefly grounded in 2013 due to a battery fire, but have since developed a good safety record.
Indian aviation authorities launched a broader review immediately after the crash and intensified their oversight of the country's airlines. They found instances of inadequate maintenance procedures and a flight with worn tires. But they found no evidence of broader risks to Air India's 787 fleet.
