aviation

Exactly 30 days after the Air India 171 accident, and just in time to meet the ICAO deadline, India released the preliminary investigation report into the crash.

It confirms the intel from earlier this week that both fuel switches were digitally recorded to have been moved to the CUTOFF position within a second of each other, and three seconds after rotation, which caused both engines to spool down and stop producing thrust, while the ram air turbine auto-deployed to provide minimal electrical power and hydraulics.

One of the pilots is heard on the cockpit voice recorder asking his colleague why he cut off the fuel, which the other denies doing. Both fuel switches are then recorded to be set back to the RUN position ten seconds after CUTOFF, which was too late for the engines to spool back up and resume delivering enough thrust to avoid impact.

All others configuration settings (flaps at 5, throttle at takeoff thrust, reverse levers stowed, etc) were found to be in their standard and expected position. The only exception was the landing gear that was still extended, but this unsurprising because cannot be retracted without hydraulics from the engines. The primary cause of the accident is, clearly, insufficient thrust due to fuel starvation in both engines.

Now the attention will shift to understanding how and why the fuel switches were moved to CUTOFF.

An accidental flipping of the switches is unlikely (they each need to be lifted, pulled back, and set down — a so-called “locking feature” to prevent unwanted action). However, there was a 2018 FAA airworthiness bulletin calling for the inspection of the exact same switches fitted on the Boeing 737, which had been found installed without the locking feature in some instances. There’s no indication yet that this may have also been the case on the B787.

Malicious intent from someone in the cockpit (either pilot, or an observer in the jump seat) will now be scrutinized as being the most plausible cause.

Analysis will also be required into whether the fuel switches could have turned off electronically by themselves, and whether this would have been recorded just the same way by the flight data recorder as a physical cutoff. Despite them being physical switches, they are electronic interfaces that are not mechanically linked to the fuel lines, and the full authority digital engine control (FADEC) software does control them.

Link to the preliminary report (see p. 14 in particular): https://static01.nyt.com/newsgraphics/documenttools/3e6e572bb0cd57e7/8d66090a-full.pdf

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