New Delhi: The preliminary report of the Aircraft Accident Investigation Bureau (AAIB) on the June 12 crash of Air India flight AI-171 in Ahmedabad seems to have thrown up more questions than it has answered. The report, released in the early hours of Saturday, claims that fuel supply to both engines was cut-off immediately after take-off.
This happened after the engine fuel cutoff switches were moved from the ‘RUN’ to ‘CUTOFF’ positions within a second of each other, immediately after the aircraft left the ground.
What happened thereafter was a communication between the two pilots. Cockpit voice recordings captured one pilot asking: “Why did you cut the fuel?” The other replied, “I did not.”
According to the report, “Fuel cutoff switches activated mid-flight: At 13:38:42 IST (08:08:42 UTC), the aircraft reached 180 knots IAS. Immediately after, both engines’ fuel cutoff switches moved from ‘Run’ to ‘Cutoff’.”
The report goes on to say that an attempt was made to relight the engines by returning the “fuel switches for engines 1 and 2 to ‘Run’ within seconds. Exhaust Gas Temperatures (EGTs) for both engines rose, indicating relight efforts.”
“While Engine 1’s core deceleration halted, reversed, and began progressing toward recovery after initial failure, engine 2 relit but could not arrest core speed deceleration, despite repeated fuel reintroduction attempts. Engine and Aircraft Flight Recorder (EAFR) data confirmed that N2 values in both engines fell below minimum idle speed during the incident,” the report states.
It was also noted by AAIB that the Engine and Aircraft Flight Recorder (EAFR), located at in the tail portion of the aircraft, was found to be substantially damaged in the incident and could not be downloaded using conventional methods.
Co-pilot Clive Kundar was flying the Boeing 787-8 Dreamliner at that time, while pilot-in-command Sumeet Sabharwal was ‘pilot monitoring’ for this flight. Sabharwal had nearly 8,600 hours on the Boeing 787 under his belt, while Kundar had over 1,100 hours, both of which were considered more than sufficient.
The report mentioned that both pilots had an adequate rest period before the flight.
After a few seconds in the CUTOFF position, the switches for both engines on the doomed aircraft transitioned from CUTOFF to RUN position – evidently an attempt by the pilots to recover thrust in the engines, but given the extremely low altitude of the aircraft, they did not have enough time for the engines to recover to a level that would have allowed them to climb to safety.
According to the 15-page report, the flight lasted around 30 seconds between lift-off and crash. The report noted that at this stage, there are no recommended actions to operators of Boeing 787-8 aircraft and GE GEnx-1B engines.
According to airline pilots and experts, the movement of the fuel control switches — critical switches that allow and cut fuel flow to the plane’s engines — have to be deliberate actions and their accidental movement is next to impossible. The switches have brackets on either side to protect them.
Additionally, there is a stop lock mechanism that requires the pilots to lift the switch before moving it from either of its two positions — RUN and CUTOFF — to the other. The report did not mention whether the investigators have so far been able to ascertain if the switches were toggled by one of the pilots or not.
These switches are usually moved only when the aircraft is on ground — to start the engines before departure and to shut them down after landing. Movement of either of the switches during the flight would be required only in the event of the corresponding engine failing or suffering enough damage that would require shutting off fuel supply to it to ensure flight safety.
The pilots may also switch off fuel supply and then immediately switch it on if they believe that the affected engine could be restarted safely.
It needs to be mentioned that the preliminary report is only an account of the initial findings of the investigation, and is subject to change on the basis of the progress of the probe over the the coming months. Air crash accidents are extremely complex and time-consuming exercises, taking months and sometimes even years to conclusively identify the causes. The AAIB is expected to release the final probe report within a year of the crash.
Notably, the preliminary report mentioned that the US Federal Aviation Administration (FAA) had in 2018 issued a Special Airworthiness Information Bulletin (SAIB) regarding the “potential disengagement of the fuel control switch locking feature”. Air India, however, did not carry out the inspection as the SAIB was merely advisory and not mandatory.
According to the report, the scrutiny of maintenance records revealed that the cockpit’s throttle control module — which houses the fuel control switches among others — was replaced in 2019 and 2023, but the reason for replacement was not linked to the fuel control switches. It added that no defect was reported pertaining to the fuel control switch since 2023 on the aircraft.
“All applicable Airworthiness Directives and Alert Service Bulletins were complied on the aircraft as well as engines,” the report said.
The report also stated that the flap position was at 5 degrees, which is consistent with take-off flap settings. There had been some speculation earlier that the aircraft’s flaps may not have been in the right configuration for take-off and thereby did not provide sufficient lift to the aircraft.
The report also mentions that there were no weather-related issues with the flight and the aircraft’s take-off weight was well within permissible limits for the given conditions. It added that there were no ‘dangerous goods’ on board the plane.
On the status of the investigation, the initial report said that wreckage site activities including drone photography and videography have been completed, the wreckage has been moved to a secure area near the airport, engines have been quarantined at a hangar at the Ahmedabad airport, components of interest have been quarantined for further examination, black box data is being analysed in detail, statements of eye witnesses and the lone survivor have been taken, and more details are being gathered based on additional leads.
The report added that only limited amount of fuel samples could be retrieved from the aircraft, and will be tested at a suitable facility. Fuel samples taken from bowsers and tanks used to fuel the aircraft at the Ahmedabad airport were found to be satisfactory. Dual engine failure due to fuel contamination was another theory doing the rounds.
“At this stage of investigation, there are no recommended actions to B787-8 and/or GE GEnx-1B engine operators and manufacturers. Investigation is continuing and the investigation team will review and examine additional evidence, records and information that is being sought from the stakeholders,” the preliminary report stated.
