Air India plane crash report: Fuel switch explainer

New Delhi: The Aircraft Accident Investigation Bureau’s (AAIB) preliminary probe report on the fatal Air India plane accident has put the spotlight on the fuel switches of the crashed Boeing 787-8 and the confusion among the two pilots over the switches being cut off.

Fuel switches regulate the flow of fuel into an aircraft’s engines. The switch has two positions — ‘RUN’ and ‘CUT OFF’ — and are used to start or shut down engines.

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According to a veteran pilot, the position of a fuel switch cannot be changed accidentally and there is a procedure in place.

The fuel switches are generally guarded with brackets so that there are no accidental movements. The switches have to be first pulled up before changing their position, the pilot said.

In a Boeing 787 Dreamliner, the fuel switches are located under the thrust levers.

Fuel switches were cut off

In the case of the ill-fated AI 171 flight, the fuel switches to the two engines of the aircraft were cut off within a gap of one second and later, they were switched on.

“Thrust lever is like a car accelerator pedal, the more you open it the more power you get , the less you open it the less power you get. There are two extreme positions– one is idle power and one is full power. Then there is a fuel control switch which has got two positions– cut off and run. So when you shut down the engine or the engine is not running the fuel control switch is in cut off mode and fuel is being fed into the engine,” the pilot explained.

What happens when engine starts

Now when the engine starts, it is a two-step procedure where the start selector is put on and then fuel control is put to run mode, as per the veteran pilot.

“Then automatically, a lot of things happen inside. The engine starts running means fuel is being fed into the engine. The thrust lever is at idle, and the engine starts running at idle. This movement of the fuel control from cut off to run is controlled by an electronic gate, requiring you to switch it to run or cut off deliberately. That’s a safety feature,” he said.

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“Now what has happened is after rotation, normally the moment the aircraft lifts off from the ground, there is an air-ground sensor in the tyre which senses and lets the aircraft system know now I am in the air or now I am on the ground. So the moment it senses in the air and we see it on our instrument that the aircraft is positive climb, which is the first step, the pilot flying should say gear up.

“So what I see here is that neither the transcript has mentioned nor anybody is talking about whether the pilots call positive climb gear up or not. Why is the gear lever still down? What may have happened is that at the point of wanting to do gear up…both engines either deliberately or inadvertently the switches were put off. So everyone forgot about the gear,” he explained.

“And then one of the pilots asked why did you put it off and either he, the one who has noticed it or the pilot who cut it off realised oh what have I done and they have put it back to run but it was too late.”

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