French crash investigation advancing

By Tim Hepher and Peter Murphy

PARIS/SAO PAULO (Reuters) - French investigators are getting closer to understanding the cause of an Air France crash that killed 228 people, but difficult search conditions in the Atlantic Ocean are hampering the process, France's chief air disaster investigator said on Wednesday.

The Airbus 330 crashed into the sea en route from Rio de Janeiro to Paris on June 1, killing all on aboard.

The French military is using a mini-submarine to search the sea for the "black box" data and voice recorders which may offer clues to the cause.

"We are getting a little closer to our goal but don't ask me what the percentage of hope is," Paul-Louis Arslanian, head of the French BEA agency in charge of investigating the crash, told a news conference without giving details of its progress.

He said the remote location and uneven surface of the ocean where the search was focussed posed one of the biggest challenges in the air crash investigation. The uneven ocean floor means the wreckage could lie anywhere between a depth of 1 km (0.6 miles) and 4 km (2.5 miles).

The BEA has said data transmitted from the plane before it crashed indicated unreliable speed readings from the aircraft's sensors, but cautioned it was too early to say whether this contributed to the accident.

Locator beacons known as "pingers" on the flight recorders send an electronic impulse every second for at least 30 days. The signal can be heard up to 2 km (1.2 miles) away.

"The goal is to understand what happened and for that we need tools and these tools must be facts. The recorders are recorders of facts. If we had them we would have more facts at our disposal," Arslanian said.