The Aircraft Accident Investigation Bureau (AAIB) has published its preliminary report into the crash of Air India Flight 171, presenting the first official explanation of the June 12 disaster that killed 260 people. Here’s what the report reveals and what still isn’t clear.
How did the Crash Happen?
As per the initial findings, both of the engine fuel cutoff switches ‘changed from RUN to CUTOFF position one after another with time interval of 01 sec’ simultaneously at 08:08:42 UTC, exactly when the plane was flying at its highest speed of 180 knots while taking off. The quick change off shut off fuel to both the engines, and they lost power.
Though, the report doesn’t yet explain why the fuel switches moved. It’s still to be ascertained whether this was due to human error, a mechanical failure, or electronic malfunctioning issues at the center of the ongoing inquiry.
Investigations have already ruled out several possible reasons:
- Weather conditions were good with light wind and clear skies.
- No bird strikes were reported by either CCTV or on physical inspection.
- Aircraft configuration was as it should have been, flaps set at 5 degrees for takeoff and normal retraction of landing gear.
- Weight and balance were within standard parameters.
- Fuel quality was checked; airport truck samples were acceptable.
- Both engines exhibited no prior faults and performed normally until the fuel cutoff.
Was the Pilot Responsible?
At this point, it’s too soon to tell. The cockpit voice recorder caught an illuminating exchange: one pilot questioned the other as to why he had shut off the fuel, to which he received the answer that he had not.
This exchange is indicative of a pattern wherein one pilot was concerned when the fuel cutoff, but his partner denied making the move.
While this doesn’t necessarily rule out pilot error, it does suggest the cut-off may not have been intentional.
What did Occur in the Cockpit?
The flight was flown by First Officer Clive Kunder, the pilot flying (PF), with Captain Sumeet Sabharwal as the pilot monitoring (PM), a normal setup where the junior pilot flies under the guidance of the captain.
The AAIB only provides a paraphrase of the cockpit conversation surrounding the accident: “one of the pilots is heard asking the other why did you cutoff. The other pilot replied that I did not do so.”
It does not specify which pilot uttered which sentence. Further analysis of the cockpit tapes could provide more, such as warning alarms or other important audio.
Were the Crew Able to Salvage the Plane?
The pilots did attempt to recover determinedly. In 10-14 seconds after the fuel loss in the engines, they reset both switches to ‘RUN’ position (Engine 1 at 08:08:52 UTC, Engine 2 at 08:08:56 UTC). The engines started automatic attempt to restart Engine 1 indicated partial recovery, and Engine 2 began a relight.
Sadly, it was too late. With the plane only around 625 feet in the air when the engines stalled, there just wasn’t enough altitude or time. Jet engines can be restarted during flight, but generally require more time and greater altitudes than the paltry 29 seconds remaining prior to impact.
Any Pre-Existing Technical Issues?
The report indicated that the aircraft, VT-ANB, had a good maintenance record with current certificates and no recent problems attributed to fuel control switches.
But there was one significant safety advisory. In 2018, the US FAA published a Special Airworthiness Information Bulletin (SAIB No. NM-18-33) regarding potential issues with fuel switch locking mechanisms on Boeing aircraft, including the 787 model. The bulletin followed reports of switches fitted with unlocked locking mechanisms on Boeing 737s.
Since this was a recommended and not a required directive, Air India did not carry out the suggested inspections. The airline had already replaced the throttle control module twice (in 2019 and 2023), but these measures were not related to any concerns about fuel switching.
What Warned the FAA Bulletin?
The 2018 bulletin warned that fuel switch lock mechanisms may be released, making the switches more susceptible to accidental movement from vibrations or accidental contact. The locking mechanisms are put in place specifically to avoid such accidental switch movement.
Though the FAA did not find this severe enough to warrant an ordered directive, it still recommended airlines check these mechanisms.
What’s Next in Investigation?
It’s important to note that this is merely an initial report. The AAIB stressed that “the information is preliminary and subject to change.” Investigators are still working on a number of fronts, including:
- A more detailed exploration of about 49 hours of flight data and two hours of cockpit voice recordings.
- Analyzing recovered fuel samples from the plane.
- Performing a close mechanical analysis of the fuel switches and associated systems.
- Interviewing more witnesses, technical personnel, and experts.
The AAIB says, “further details are being obtained based on the initial leads,” and the team will ‘consider and analyze further evidence, records and information being pursued by the stakeholders’. A final report determining probable cause and recommending safety actions is likely to take several months or even years to be concluded.
