Investigators seek clues to crash

Investigators in Bahrain probing the crash of Gulf Air flight GF072 initially found few clues as to why the plane crashed, killing all 143 people on board.

Black Box

Built to withstand crash impact

Can tolerate extreme temperatures and underwater pressure

Logs speed, altitude, heading and other technical data

Records cockpit conversations and radio links to the control tower

The crew made no distress call before the plane went down.

Investigators say that, based on continuing analysis of the Airbus A320's flight data and cockpit voice recorders, the pilot failed to slow down as he tried to land - despite cockpit system warnings.

But they say it is still too early to say whether pilot error caused the crash.

Eyewitnesses said that the plane circled the airport, as if it was waiting to land.

"The plane was near the runway, but didn't land," said one man, asking to remain anonymous.

"It circled two times and the third time it crashed into the sea," said an air traffic controller at Bahrain airport.

Too fast?

Investigators' accounts of the plane's final moments indicate that the crew was having trouble controlling the plane, which appeared to have accelerated rather than reduced speed after the warning.

Although Captain Ihsan Shakeeb had 21 years experience in the cockpit, he had only recently been appointed to the command of the plane.

The control tower in Bahrain reportedly did not ask the pilot about the reason for making several circuits of the airport before attempting to land.

But local press reports said the pilot had been requested not to land, because the plane's speed was too high and it was in danger of overshooting the runway.

The control tower instructed Captain Shakeeb to climb again and make two circuits to reduce speed, before reapproaching the runway.

Investigators must piece together the evidence

However, the plane was reportedly still flying too fast and as the pilot made a small turn at high speed, he lost control and the plane nosedived into the sea.

Airline experts say that circuits involve a series of technical procedures which, although straightforward in theory, could cause problems under pressure.

Another theory is that the landing gear was disabled, and the plane made the circuits while the captain tried to resolve the problem.

However, if a pilot is unable to lower the wheels, experts say the plane would try and land on a carpet of foam, specially spread on the airport runway.

Any landing on water is likely to more risky, because even at low speeds, a wing might clip the water and send the plane spinning out of control.

The fact that the waters off Bahrain are shallow would make little difference, because a large aircraft crashing at speed would break up, no matter what it hit.

Engine problem

Bahrain television initially quoted unidentified officials as saying the Airbus plunged into the sea after an engine caught fire.

But the country's civil aviation department issued a statement dismissing the report as "pure speculation".

Even with only one working engine, a plane should be able to land

Nonethless, the possibility of an engine fault must always be considered by investigators.

The plane's manufacturer, Airbus Industrie, said the plane was powered by two CFM56-5 engines, built by the US company General Electric and the French concern Snecma.

The CFM56 is used on thousands of A320s, and experts say it is highly reliable.

In any case, the failure of one engine would be unlikely of itself to cause a crash, as a modern jet could keep flying with its second engine alone.

A more serious problem would be so-called uncontained engine failure, in which the turbines inside the engine disintegrate and destroy the engine casing.

The casing is designed to be strong enough to withstand such explosions, which can be caused by problems ranging from technical malfunction to birds being sucked into the engine.

Gulf Air officials in Cairo have said there was nothing wrong with the plane when it took off for Bahrain.

"It arrived OK, the check was OK and it left OK," said a member of Gulf Air's ground staff.