Page last updated at 20:03 GMT, Thursday, 2 July 2009 21:03 UK

Piecing together fate of Air France jet

Plane wreckage at Recife, Brazil (19.6.09)
Debris from the Air France crash has been brought ashore at Recife, Brazil

By Tom Symonds
Transport correspondent, BBC News

The report by French crash investigators into the crash of an Air France plane in the Atlantic last month runs to 126 pages. It is remarkably detailed considering how few facts have so far been established.

The flight data recorder and cockpit voice recorder have not been found. The small acoustic locator beacons fixed to them are running out of power, but the French, US and Brazilian search teams are not giving up.

They will scour the ocean until 10 July.

So the focus of the detective work has been in examining 600 pieces of wreckage plucked from the sea over the past month, since 228 people on the plane were killed when it came down en route from Rio de Janeiro to Paris.

Some pieces are instantly recognisable - the plane's huge tail fin was spotted quickly. But there are sections of the cabin, bits of the toilet, and smaller fragments of the engine.

Part of Air France flight 17.6.09
How the wreckage is damaged reveals how the plane broke apart

Lifejackets have also been found, un-inflated.

Investigators have examined how the parts have been torn from their fixings.

If they had shown signs of wrenching in several directions that might suggest a mid-air breakup, perhaps due to turbulence.

Instead the parts appear to have been compressed in one particular direction. Some have marks suggesting an impact on the bottom of the plane first.

The hypothesis is that the aircraft was intact when it hit the ocean, belly first, a fast vertical acceleration.

The other major line of inquiry is the analysis of 24 messages sent out over the ACARS network.

This is an automated satellite and radio system used for the transmission of operational information and fault reports.

Some of the messages suggest systems going off line, including the automatic throttle, the autopilot and the sensor that detects rapid changes of wind.

Cabin pressure

There was a warning the cabin pressure was changing, and that the plane was operating with reduced fly-by-wire capabilities.

Most worrying are the messages indicating the plane's systems had unreliable readings of its speed - in one case detecting a decrease of around 25mph over the period of one second.

This may be due to problems with the plane's three pitot sensors, mounted on the nose, which collect information about air speed. If they had failed they may in turn have tripped a number of the plane's computers.

But the problem with this information is discovering whether it represents the symptoms of technical failures, or the cause of them.

Experts say only the data and voice recorders - the black boxes - will really explain the crash, and finding them now seems unlikely.

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