CNN.com - Spotlight on Concorde engine

PARIS -- A photograph and eyewitness accounts of flames and smoke billowing from the underside of the stricken Air France Concorde is expected to focus crash investigators' attentions on the jet engines.

An Air France spokesman also confirmed on Wednesday that work had been carried out on an engine of the ill-fated airliner soon before take-off, causing a flight delay, but said it was too early to know if it was a factor in the acccident.

Concorde's four powerful engines are unique in commercial aviation, propelling the plane to 246 mph within 30 seconds of takeoff.

The enormous thrust that accelerates the Concorde and powers it through the sound barrier stems from afterburner technology originally designed for military aircraft.

Engines similar to those on the aircraft that crashed

This afterburner system is used by all supersonic aircraft at takeoff, and combines the power of the jet engine with extra thrust produced by reignited fuel injected into the rear of the engines.

Exhaust gases streaming out of the engine are also reheated and ignited in a process called post-combustion. It is this process that is responsible for the orange and red glow referred to as afterburn.

Concorde's afterburner is turned off 30 seconds after takeoff, before it heads towards a cruising altitude of 60,000 ft and a top speed of 1,345 mph, or twice the speed of sound.

The four Rolls Royce/SNECMA Olympus 593 engines are each capable of producing 38,000lb thrust, allowing the plane to take off comfortably on just three engines. The Concorde which crashed was certified to be capable of climbing away successfully on just two engines.

But experts say a fire in one engine could spread to an adjacent engine under the plane's delta-shaped wing and lead to further complications.

Enormous strain is put on the engines and the surrounding structure as they travel at supersonic speeds.

The plane endures greater extremes of heat and air pressure than any other commercial aircraft, with temperatures on the Concorde's skin reaching as high as 600 C.

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