(Recasts with updated sourcing)

NEW DELHI, July 18 (Reuters) - A cockpit recording of

dialogue between the two pilots of the Air India flight that

crashed last month supports the view that the captain cut the

flow of fuel to the plane's engines, said a source briefed on

U.S. officials' early assessment of evidence.

Below are a few facts about engine fuel switches, their

functions in the aircraft and their movements on the Air India

flight.

WHAT ARE FUEL SWITCHES?

They are switches that regulate fuel flow into a plane's

engines. They are used by pilots to start or shut down engines

on the ground or to manually shut down or restart engines if an

engine failure occurs during a flight.

Aviation experts say a pilot would not be able to

accidentally move the fuel switches that feed the engines. But

if moved, the effect would be immediate, cutting off engine

power.

There are independent power systems and wiring for the fuel

cutoff switches and the fuel valves controlled by those

switches, according to U.S. aviation safety expert John Cox.

WHERE ARE THE FUEL SWITCHES LOCATED?

The two fuel control switches on a Boeing 787, in Air

India's case equipped with two GE engines, are located

below the thrust levers.

The switches are spring-loaded to remain in position. To

change one from run to cutoff, a pilot has to first pull the

switch up and then move it from run to cutoff or vice versa.

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

WHAT HAPPENED ON THE FATAL AIR INDIA FLIGHT?

According to the flight recorder, a few seconds after

takeoff, switches for both engines transitioned to 'CUTOFF' from

'RUN' one after another with a time gap of one second. As a

result, the engines began to lose power.

One pilot was heard on the cockpit voice recorder asking the

other why he cut off the fuel. "The other pilot responded that

he did not do so," the report said.

The report did not identify which remarks were made by the

flight's captain and which by the first officer.

The first officer was at the controls of the 787 and asked

the captain why he moved the fuel switches into a position that

starved the engines of fuel and requested that he restore the

fuel flow, the source briefed on U.S. officials' early

assessment told Reuters.

Both switches were flipped back to 'RUN', according to the

preliminary report, and found in the 'RUN' position at the crash

site.

When fuel control switches are moved from 'CUTOFF' to 'RUN'

while the aircraft is in flight, each engine's control system

automatically manages a relight and thrust recovery sequence of

ignition and fuel introduction, the report said.

"No sane pilot would ever turn those switches off in

flight," especially as the plane is just starting to climb, U.S.

aviation safety expert John Nance said.