The Aircraft Accident Investigation Bureau (AAIB) has released its preliminary report into the Air India Flight 171 crash, shedding light on the chaotic final seconds before the plane plunged from the sky, killing 241 people onboard, with one survivor.
The report, made public shortly after midnight on Saturday—exactly a month after the country’s deadliest aviation tragedy in decades—offers the first official insight into what went wrong.
Among the most chilling revelations in the AAIB's preliminary report is a cockpit exchange between the two pilots seconds after takeoff, in which one pilot noticed that fuel had been cut off to both engines and asked, “Why did you cut off?” The other responded, “I did not do so."
This brief but critical interaction, captured on the cockpit voice recorder, points to a dual-engine failure triggered by a simultaneous shutdown of fuel supply. The Air India flight took off at 1:38 PM after receiving clearance, and seconds later, it crashed.
Timeline of the final moments of AI 171:
The AAIB gave details about the final sequence of events using data from air traffic control (ATC), the aircraft’s emergency and flight data recorders (EAFR), and CCTV footage from the airport. The timeline, detailed in IST (Indian Standard Time), shows that the flight proceeded normally until the moment of liftoff.
- 13:13:00 IST – The aircraft requested pushback and startup.
- 13:13:13 IST – ATC approved pushback.
- 13:16:59 IST – ATC approved engine startup.
- 13:19:12 IST – When asked, the crew confirmed they needed the full length of Runway 23.
- 13:25:15 IST – The aircraft requested and received taxi clearance.
- 13:32:03 IST – Control of the flight was transferred to the Tower.
- 13:33:45 IST – The aircraft was instructed to line up on Runway 23.
- 13:37:33 IST – The aircraft was cleared for takeoff.
- 13:37:37 IST – The plane began its takeoff roll.
- 13:38:33 IST – The aircraft crossed V1 speed (takeoff decision speed) and reached 153 knots.
- 13:38:35 IST – The plane reached Vr speed (rotation speed) of 155 knots.
- 13:38:39 IST – Liftoff confirmed as sensors switched from ground to air mode.
- 13:38:42 IST – The aircraft achieved 180 knots—its maximum recorded airspeed.
The AAIB gave details about the final sequence of events using data from air traffic control (ATC), the aircraft’s emergency and flight data recorders (EAFR), and CCTV footage from the airport. The timeline, detailed in IST (Indian Standard Time), shows that the flight proceeded normally until the moment of liftoff.
- 13:13:00 IST – The aircraft requested pushback and startup.
- 13:13:13 IST – ATC approved pushback.
- 13:16:59 IST – ATC approved engine startup.
- 13:19:12 IST – When asked, the crew confirmed they needed the full length of Runway 23.
- 13:25:15 IST – The aircraft requested and received taxi clearance.
- 13:32:03 IST – Control of the flight was transferred to the Tower.
- 13:33:45 IST – The aircraft was instructed to line up on Runway 23.
- 13:37:33 IST – The aircraft was cleared for takeoff.
- 13:37:37 IST – The plane began its takeoff roll.
- 13:38:33 IST – The aircraft crossed V1 speed (takeoff decision speed) and reached 153 knots.
- 13:38:35 IST – The plane reached Vr speed (rotation speed) of 155 knots.
- 13:38:39 IST – Liftoff confirmed as sensors switched from ground to air mode.
- 13:38:42 IST – The aircraft achieved 180 knots—its maximum recorded airspeed.
Everything appeared to be proceeding normally until this point, with no anomalies reported in communication or aircraft behaviour, as per the preliminary report. Then, suddenly, both engines began to shut down.
- 13:38:43–44 IST – Fuel cutoff switches for both engines transitioned from ‘RUN’ to ‘CUTOFF’—just one second apart. The engines began losing thrust immediately.
- 13:39:05 IST – The pilot issued a distress call: “MAYDAY.”
Within seconds of liftoff, the aircraft began losing altitude and was unable to clear the airport perimeter wall. CCTV footage confirmed the Ram Air Turbine (RAT), a backup power-generating device that deploys when the aircraft loses engine power, was activated moments after takeoff.
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The report, notably, confirmed no significant bird activity near the flight path, ruling out a bird strike as a possible cause.
Technical mystery lingers
The twin engine shutdown is currently unexplained. The fuel cutoff switches, critical for regulating fuel supply, should not have shifted simultaneously under normal circumstances. Yet, both transitioned to ‘CUTOFF’ in perfect sequence.
The AAIB report, however, mentioned that while Engine 1 showed signs of recovery after its core speed stabilised, Engine 2 continued to lose core speed and failed to recover despite being successfully relighted.
Also Read | Air India flight 171 crash: What AAIB preliminary report reveals – and doesn’t
That mystery deepened with the voice recorder capturing one pilot questioning the ‘CUTOFF’—and the other denying having performed it.
The report does not currently assign blame or recommend changes for either Boeing, the manufacturer of the B787-8 aircraft, or General Electric, which makes the GE GEnx-1B engines used in the jet.
Boeing responds
“We will defer to the AAIB to provide information about AI171, in adherence with the United Nations International Civil Aviation Organization protocol known as Annex 13,” a brief statement from Boeing read.