Ahmedabad Air India plane crash: How does the fuel switch of a Boeing 787-8 work: Explained

The fuel control switches on a Boeing 787-8 aircraft are critical cockpit controls that regulate the flow of fuel to each of the two engines. Their primary purposes are to start or shut down the engines during ground operations and to manually stop or restart an engine in the event of an in-flight emergency, such as an engine failure or a fire.

The switches are located immediately behind the throttle levers, between the two pilots’ seats on the center pedestal.

Each engine has its own switch, with two positions: RUN, when fuel flows to the engine, and CUTOFF, when fuel supply is stopped.

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The switches are guarded by brackets and feature a spring-loaded locking mechanism. To move a switch from RUN to CUTOFF, a pilot must lift the switch over a metal stop before sliding it. This design is provided to make accidental activation more unlikely.

On the ground, pilots set the switches to RUN to start the engines and to CUTOFF to shut them down after landing. In flight, the switches are kept in RUN. Moving a switch to CUTOFF immediately stops fuel flow to the corresponding engine, causing it to shut down and lose thrust. This also disables the engine-driven generators, potentially affecting the aircraft’s many electrical systems.

In emergencies, such as if an engine has caught fire, the relevant switch will display a red light, signalling to the crew that it should shut that engine down.

Commercial twin-engine aircraft like the Boeing 787-8 are designed to maintain safe flight with only one engine if required. However, if both fuel switches are erroneously moved to CUTOFF, both engines will lose power, eliminating all engine redundancy and leaving the aircraft without thrust.

Aside from the metal stop, both the switch and the associated fuel valves have separate power and wiring systems for redundancy.

In fact, a 787-8 aircraft’s fuel shutoff valves are spring-loaded to close, and cut off fuel, if they lose electrical power, and the system relies on multiple redundant power sources. However, a major electrical failure or software glitch could cause both valves to close, again removing engine redundancy by shutting down both engines.

If a pilot inadvertently moves a switch to CUTOFF during flight, the aircraft’s systems will attempt an automatic engine relight and try to reintroduce fuel to the engine when the switch is returned to RUN, although this may not always succeed in restoring full engine power.