Page last updated at 15:25 GMT, Monday, 8 June 2009 16:25 UK

Answers elusive in Air France crash

The Brazilian Navy Frigate Bosissio anchored in front of the harbour in Fernando de Noronha, Brazil on June 6
The best clues to the crash - the flight data recorders - remain lost at sea

By Chris Yates
IHS Jane's aviation analyst

As more bodies are pulled from the sea, few answers are forthcoming about the cause of last week's Air France A330 crash off the Brazilian coast.

Modern aircraft are robust machines with high levels of redundancy built in, and rarely fall out of the skies due to a single systems failure.

When they tragically occur, accidents are invariably the result of a complex sequence of events that come together and conspire to doom an airliner, despite the best efforts of those in control to avert a disaster.

Seven days after Air France flight 447 disappeared, we know precious little as to what occurred aboard the airliner that night.

Relatives of passengers leave a church in Roissy-en-France, Paris, 6 June
Relatives of the 228 people on the plane are waiting for an explanation

We have been told that weather in the region was poor at the time of the crash, but aircraft are designed to withstand all but the most destructive forces that nature can throw at them.

We know that in the few precious minutes before the jet plunged towards the ocean, automated monitoring systems began to transmit a sequence of 24 short error messages.

Although they indicated that critical systems were beginning to shut down, we have no understanding about what precipitated this flurry of data traffic.

We understand that the auto-pilot was disengaged at the time these error messages were sent.

But we have no clues as to whether this was an un-commanded disengagement prompted by some other systems failure, or whether the pilot took control in a valiant but ultimately failed attempt to rescue his aircraft.

Black boxes key

These slivers of information are the first pieces in a gigantic jigsaw puzzle that will take significantly longer than might otherwise have been the case had the airliner come down in a more accessible location.

Plane at the French Air Base in Dakar, 7 June
Planes equipped with special radar are searching a vast wreckage field

With a wreckage field strewn across a swath of the Atlantic Ocean some 1,000km (600 miles) north-east of Brazil's Fernando de Noronha islands, it is one of the most difficult areas in which to conduct a search and recovery mission.

The discoveries of human remains and some wreckage over the weekend may yield further important clues to the cause of the crash.

But it is imperative that the larger sections of the aircraft be discovered as well, and most importantly, that the so-called black boxes are found and recovered for analysis.

This is easier said than done. The nature of the crash may mean that debris is scattered over a very wide area and currents could have carried key remains a substantial distance from the point of impact.

Sophisticated sonar equipment is being deployed to positively identify the submersed wreckage field, and listen out for sonar beacons we hope are still attached to the flight recorders.

A lookout near a former Air France communications base at Fernando de Noronha Island in northeast Brazil, 5 June
Time is ticking down in the mystery of the crash off the Brazilian coast

But the clock is ticking down since these beacons will operate to a maximum of only 30 days. Beyond this time, the recorders may be lost forever in the depths of the ocean.

We have also been told that speed sensors aboard the aircraft might have malfunctioned and this is a known problem specific to the A330 and A340 family of aircraft.

Sensors aboard this flight had not been replaced as per a recommendation by Airbus, the aircraft manufacturer.

It is important to stress that this information represents only one more piece of the jigsaw. This was a recommendation and not a safety-critical requirement.

There are many other ways to determine speed and it would be dangerous at this stage to draw conclusions from this revelation.

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