With only eight days to go before the black-box signals from Air France flight 447 die out, French search teams are hoping that a signal they detected yesterday actually comes from the flight data recorders.
 
Le Monde newspaper reported on its website Tuesday that a mini-submarine had set out after French navy vessels picked up a “very weak” signal.

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But the French bureau investigating the crash said the search teams were simply “checking out any sound” that might lead to the flight recorders and that the black boxes have not been detected.

“Finding and retrieving the black boxes would be a milestone for the investigation,” said Pierre Sparaco, European columnist at Aviation Weekly magazine. But he cautioned that the data recorders were unlikely to answer all of the questions surrounding the crash.

The doomed Airbus A330 crashed into the Atlantic Ocean after running into thunderstorms during its journey from Brazil to France, killing all 228 people aboard. Research teams are scouring an area of 80 square kilometres using US Navy underwater listening devices attached to 6,000 metres of cable to scan the depths of the Atlantic for the black-box signals.

These data collection devices, which are usually mounted in the aircraft’s tail, are crucial to the current investigation into the causes of AF 447's sudden crash.

When the French mini-submarine Nautile reaches the seabed thousands of kilometers underwater, it will be looking for small, hi-tech devices that are not actually black, but bright orange.

Withstanding a catastrophic crash
 
Industry professionals usually refer to the black boxes as cockpit voice recorders (CVR) and flight data recorders (FDR). Besides recording conversations in the cockpit, these units also collect key flight data such as airspeed, altitude and aircraft pitch. Both recorders are housed in strong materials, such as titanium, and insulated to survive catastrophic accidents.
 
The units are tested to withstand temperatures of more than 1,000 degrees celsius for up to 30 minutes, the immense pressure of the deepest ocean seabed and crash impacts many times the force of gravity. Their bright orange colour make the so-called black boxes easier to spot for investigation teams visually surveying the crash site.

But the flight recorders may not have been able to register the cause of the crash.

“The flight recorders could show that everything was working fine on board, until the plane breaks up and the recording is suddenly interrupted," Sparaco said.

"But the black boxes may also have worked for a few more seconds, recording crucial data,” he said.

French investigators have already found out that the aircraft speed sensors had been feeding inconsistent readings to the cockpit, but they also insisted that there was not yet any firm evidence linking the speed monitors and the AF 447 crash.