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Air India flight 171 crash: What AAIB preliminary report reveals – and doesn’t
The preliminary report reveals that both engine fuel cutoff switches "transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec".
The Aircraft Accident Investigation Bureau's preliminary report into the Air India flight 171 crash has provided the first official account of the disaster that killed 260 people on June 12. Here are the key findings and what they mean for the ongoing investigation.
What caused the crash?
The preliminary report reveals that both engine fuel cutoff switches "transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec" at 08:08:42 UTC, just as the aircraft reached its maximum speed of 180 knots during take-off. This immediately cut fuel supply to both engines, causing them to lose power. However, the report does not determine what caused the fuel switches to move — whether it was human action, mechanical failure, or electronic malfunction. That critical question remains unanswered and is the focus of the ongoing investigation.
What potential causes have been ruled out?
The investigation has eliminated several possible factors:
- Weather conditions: Described as good with light winds and clear skies
- Bird strike: No evidence found in CCTV footage or physical examination
- Aircraft configuration: Flaps were correctly set at 5 degrees for takeoff, landing gear was retracting normally
- Weight and balance: Aircraft was within normal operating limits
- Fuel quality: Samples from airport fuel trucks tested satisfactory
- Pre-existing engine problems: Both engines appeared to be operating normally until the fuel cutoff
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Does this mean the pilot was responsible?
We don't know yet. The cockpit voice recording reveals a crucial exchange: one pilot asked the other why he cut off the fuel, and the other responded saying he did not. This suggests that while one pilot noticed the fuel had been cut off, his colleague denied initiating the action.
The denial by one pilot doesn't definitively rule out human error, but it does suggest the fuel cut-off could have been unintentional.
Also Read | Pilot association questions direction of Air India crash probe: ‘Presumes guilt’
What happened in the cockpit?
The flight was being operated with First Officer Clive Kunder as the pilot flying (PF) and Captain Sumeet Sabharwal as the pilot monitoring (PM)—a standard arrangement where the more junior pilot flies while the senior captain monitors and manages the flight.
The report provides only a paraphrased account of cockpit communications pertaining to the fuel cut-off, not direct quotes or any other words that may have been spoken. According to the AAIB, "one of the pilots is heard asking the other why did you cutoff. The other pilot responded that I did not do so."
The report doesn't specify which pilot made which statement. Additional cockpit voice recorder analysis may reveal more details about crew communications and other audio, such as any alarms going off.
Could the crew have recovered the plane?
The pilots made a valiant attempt to save the aircraft. Within 10-14 seconds of the fuel cutoff, they moved both fuel switches back to the "RUN" position (Engine 1 at 08:08:52 UTC, Engine 2 at 08:08:56 UTC). Both engines began automatic restart sequences, with Engine 1 showing signs of recovery and Engine 2 attempting to relight.
However, recovery was ultimately impossible due to insufficient time and altitude. The aircraft was only about 625 feet above ground when the engines failed, and engine restart procedures require significantly more time than the 29 seconds available before impact. Modern jet engines can restart in flight, but typically need several minutes and higher altitudes to complete the process successfully.
Were there any problems with the plane?
The aircraft VT-ANB had a clean maintenance record with no reported fuel control switch defects since 2023. All required inspections were current, and the aircraft had valid airworthiness certificates.
However, there was a relevant safety concern. In 2018, the US Federal Aviation Administration issued Special Airworthiness Information Bulletin (SAIB) No. NM-18-33 regarding potential problems with fuel control switch locking mechanisms on Boeing aircraft, including the 787 model. The bulletin was issued after reports that fuel control switches on Boeing 737s were installed with their locking features disengaged.
Crucially, Air India did not carry out the suggested inspections because the bulletin was advisory rather than mandatory. The airline had replaced the aircraft's throttle control module twice—in 2019 and 2023—but these replacements were unrelated to fuel switch issues.
What did the switches advisory pertain to?
The 2018 FAA bulletin addressed concerns about fuel control switch locking mechanisms that could become disengaged. These locking features are designed to prevent inadvertent movement of the fuel switches. When disengaged, the switches could potentially be moved more easily by vibration, inadvertent contact, or other factors.
While the FAA didn't consider this serious enough to issue a mandatory directive, the bulletin recommended inspections to ensure the locking mechanisms were properly engaged.
What happens next?
It's important to emphasise that this is a preliminary report, and findings could shift significantly as more evidence is gathered and analysed. The AAIB stresses that "the information is preliminary and subject to change."
The investigation continues with several key areas of focus:
- Detailed analysis of black box data: While initial analysis has been completed, investigators are conducting detailed examination of the approximately 49 hours of flight data and two hours of voice recordings to uncover additional clues
- Detailed analysis of the limited fuel samples recovered from the aircraft
- Mechanical examination of the fuel control switches and related components to determine if they malfunctioned
- Interviews with additional witnesses or connected people and technical experts
The AAIB states that "additional details are being gathered based on the initial leads" and that the investigation team will "review and examine additional evidence, records and information that is being sought from the stakeholders."
A final report, which will attempt to determine the probable cause and make safety recommendations, is expected to take months or potentially years to complete.
