Catastrophic failure

The Air India flight crash is not just a case of mechanical misfortune, but a warning shot across the bow of modern aircraft design

- UMESH RAJA

FOLLOWING THE CRASH of Air India Flight AI-171, a Boeing 787 Dreamliner that crashed moments after takeoff from Ahmedabad on June 12, there was a lot of speculation about what cost 260 lives, ranging from fuel contamination and bird strikes to pilot error and mechanical malfunction.

The absence of official data had so far created a vacuum filled with fragmented theories. However, the preliminary report of the Aircraft Accident Investigation Bureau, released on July 11, reveals that both engines flamed out within seconds of takeoff because their fuel control switches were moved to the 'cutoff' position.

The fuel switches, located below the thrust levers on the central pedestal between the two pilot seats, are manually operated and require deliberate action by the pilots to physically move them between 'cutoff' and 'run' modes.

The switches are spring-loaded, with a locking mechanism, and are also enclosed by a mechanical gate to remain in position. To change it from run to cutoff, a pilot has to first lift it manually and then move it down or vice versa. These actions have to be repeated twice for the two switches.

As per the report, both switches moved to the shutoff position within a gap of one second, which is highly unlikely under normal circumstances. It is quite a complicated situation to analyse and is hard to digest.

The switches, with advanced locking features, are designed to prevent any inadvertent operation that could starve engines of fuel. There is a critical 2018 Federal Aviation Administration advisory about these very switches, which requested inspection by carriers and operators based on reports from operational Boeing 737s. The advisory from the US body noted that some installations of these switch modules had occurred with the locking feature in disengaged mode, and if confirmed, carriers and operators were advised to replace them at the next opportunity.