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What is the fuel switch at the heart of the Air India crash investigation?

Sources briefed by U.S. officials on their early assessment of the evidence said that a cockpit recording of the dialogue between the two Air India pilots that led to the crash last month confirms that the captain stopped the fuel flow to the plane's engine.

Here are some facts about the engine fuel switches. They describe their function in the aircraft, and how they moved on an Air India flight.

What are fuel switches?

These switches regulate the fuel flow to a plane's engine. Pilots use them to shut down engines or start engines manually on the ground.

Experts in aviation say that a pilot could not accidentally move fuel switches feeding the engines. If moved, however, it would immediately cut off the engine's power.

According to John Cox, an aviation safety expert from the United States, there are separate power systems and wirings for the fuel shutoff switches and fuel valves that they control.

Where are the fuel switches located?

The fuel control switches are located under the thrust levers on a Boeing 787-8, which is equipped with two GE engine in Air India's instance.

The switches have a spring loaded mechanism that keeps them in place. The pilot must first lift the switch and then change it from cutoff to run.

There are two different modes: 'CUTOFF" and "RUN".

What happened on the fatal AIR INDIA flight?

According to the flight recording, after a few seconds of takeoff, both switches were switched from "RUN" to "CUTOFF", one after the other, with a one-second time difference. The engines started to lose power as a result.

On the cockpit voice recording, one pilot is heard asking the other pilot why he has cut off the fuel. The report stated that "the other pilot replied that he had not done so."

The report failed to identify the remarks made by the captain of the flight and those by the first officer.

Sources briefed about U.S. officials early assessment said that the first officer, who was in control of the 787 at the time, asked the captain to explain why he had moved the fuel switches so that they starved the engine of fuel. He then requested that the captain restore fuel flow.

According to the preliminary report both switches were in the "RUN" position and found at the crash scene.

The report stated that when fuel control switches from 'CUTOFF to RUN' are moved while the aircraft is flying, the control system of each engine automatically manages a sequence for relighting and restoring thrust, including ignition and fuel injection.

John Nance, an aviation safety expert from the United States, said that "no sane person would turn off those switches in flight", especially when the plane was just beginning to climb. (Reporting from Abhijith Gaapavaram, New Delhi; Dan Catchpole, Seattle; editing by Jamie Freed).

(source: Reuters)