THE PRELIMINARY report of the ongoing investigation into the June 12 crash of Air India flight AI 171 is far more detailed than what industry veterans and experts expected, and gives an indication of the direction the probe may be headed in.

The 15-page report from the Aircraft Accident Investigation Bureau (AAIB), an office attached to the Ministry of Civil Aviation, has zeroed in on the most probable primary cause of the accident— the engines being starved of fuel with the transitioning of the fuel control switches from ‘RUN’ to ‘CUTOFF’ position within a second of each other moments after lift-off.

From the cockpit voice recorder data, the report notes that one of the pilots asked the other why he cut off the fuel, to which the other pilot responded saying he did not.

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While some interpret these findings as hinting at human error, aviation industry veterans said it is too premature to arrive at any conclusion based on just the preliminary report. The report, they said, does answer some key questions, but also raises many that only a meticulous investigation would be able to clear up.

Union Civil Aviation Minister K Ram Mohan Naidu warned against jumping to conclusions and Minister of State for Civil Aviation Murlidhar Mohol said commenting or drawing any conclusion on the basis of the preliminary report wouldn’t be appropriate. “The initial finding that the fuel control switches went to cut-off mode is truly shocking. They (investigators) now have the most probable cause, and now they must investigate to figure out how it happened and why it happened. These are the key questions that must be answered in the final investigation report. The real investigation has actually started now,” a former air accident investigator told The Indian Express.

An aircraft is an extremely sophisticated and complex machine, and detailed and painstaking investigations are required to ascertain the exact cause or combination of causes. The odds that an aviation accident has a single trigger are rare; there could be many, or one leading to another. The AAIB is expected to release the final probe report within a year of the crash, as per international guidelines.

Did one of the pilots move the fuel control switches?

To be sure, the report just says the engine fuel control switches that allow and cut fuel flow to the plane’s engines transitioned from RUN to CUTOFF. It does not state these were moved by either of the pilots to the CUTOFF mode. The report does mention one pilot asking the other why he cut-off fuel supply, with the other responding he didn’t.

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Experts say accidental movement of the switches is not quite possible. The spring-loaded switches have brackets on either side to protect them and there is a stop lock mechanism that requires the pilots to lift the switch up before moving it between either of its two positions—RUN and CUTOFF.

“No sane pilot would move the switches during the flight and that too at such low altitude, unless there was a dual engine failure to be dealt with. And even that would be in coordination, not a unilateral move. Moving them by accident is also not really a possibility, as they have to be pulled up to disengage the lock and then moved mechanically to one or the other mode,” said a senior airline pilot with years of experience on the Boeing 787 aircraft.

Experts believe only the full audio and transcript of the cockpit voice recorder would be able to give more information on the pilots’ discussions and actions in the cockpit in the minutes leading up to the tragedy.

Meanwhile, a pilot association has raised concerns on the direction the AI 171 crash investigation appears to be taking. “The tone and direction of the investigation suggest a bias toward pilot error. ALPA-I categorically reject this presumption and insist on a fair, fact-based inquiry,” Sam Thomas, president of the Airline Pilots’ Association of India (ALPA-I) said in a statement. The pilots’ body has reiterated its request to be included “at the very least, as observers” in the air crash investigation.

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Fuel cut-off due to electrical, system, issues?

“Apart from looking into the action of pilots, the investigators should look if the fuel switch cut-off could be due to any other electrical or system-related issues. Could it be an electrical or software malfunction that signalled to the aircraft system that the switches were in cut-off mode, even if they had not been actually moved?” a senior airline pilot asked, considering the Boeing 787 is a modern electrically heavy aircraft.

Another airline pilot said it was theoretically possible to have such a scenario without the physical movement of the switches. Further analysis of the aircraft’s black boxes should be able to establish whether the switches were indeed moved mechanically, or whether the cut-off was due to some other issue.

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The pilots and the former aircraft accident investigator concurred that during the critical take-off phase of the flight, pilots had no business in keeping their hands anywhere close to the fuel control switches, as per established standard operating procedures. This is to prevent accidental or inadvertent toggling of any critical switch.

The fact that the preliminary report has not issued any recommendation to the operators of the Boeing 787 aircraft and the GE GEnx-1B engines suggests that the investigators, at least for the time being, do not have sufficient reason to believe that an electrical or system malfunction could have led to the fuel control switches “transitioning” to CUTOFF.

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Experts also pointed out that these switches are manual and not motorised, and cannot be physically moved by electrical signals or the plane’s avionics.

Notably, the report also makes mention of the 2018 Special Airworthiness Information Bulletin (SAIB) issued by the US Federal Aviation Administration (FAA), 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. Moreover, 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. The initial report said that no defect pertaining to the fuel control switches on the aircraft was reported since 2023.

Nevertheless, could the disengagement of the switch lock, component fatigue, or a mechanical failure move the switches? Experts said this is unlikely. The possibility of even one disengaged switch being flicked by accident was highly unlikely, they said, pointing out the report’s findings that both switches appeared to have changed positions.