Airbus recommended new sensors before crash

PARIS (Reuters) - Airbus had detected faulty speed readings on its A330 jets ahead of last week's crash of an Air France airliner, and had recommended clients replace a sensor, French air investigators said on Saturday.

But the head of France's air accident agency (BEA) said it was too soon to say if problems with pressure-based speed sensors were in any way responsible for the disaster over the Atlantic, which cost the lives of all 228 passengers and crew.

"Some of the sensors (on the A330) were earmarked to be changed ... but that does not mean that without these replacement parts, the (Air France) plane would have been defective," said BEA chief Paul-Louis Arslanian.

Airbus confirmed it had issued a "service bulletin" asking the plane's 50 or so airline operators to consider changing the speed sensors, known as Pitot tubes, but said it was an optional measure to improve performance and not related to safety fears.

"There are continuous improvements and modifications on offer on any aircraft. A service bulletin is motivated by performance or reliability," spokesman Stefan Schaffrath said.

It was not immediately clear when the bulletin had been issued and an Air France spokesman said he did not yet know whether the sensors had been changed on the stricken jet.

The doomed Air France plane, en route from Rio de Janeiro to Paris, sent 24 automated messages between 0210 GMT and 0214 GMT indicating a series of system failures before it vanished, Arslanian told a news conference.

In the middle of this stream of data was one message showing inconsistent speed readings from the A330's sensors.

The messages also indicated the autopilot was off, though it was impossible to say whether it had turned itself off, as it is designed to do when it receives suspect data, or whether the pilot had decided to turn it off, Arslanian said.

"You have a plane which transmitted a message, and it is not an exceptional or unheard of message, particularly on the A330, which detected incoherent speed readings," Arslanian said.

The plane is designed to send an error message if any two of three possible channels of speed readings available to the flight systems show a discrepancy of 30 knots or more.

"Problems had been detected (on A330s) and we are studying them," said Arslanian, adding the plane was still safe to fly.

Airbus, maker of the A330 jet that crashed on Monday, also issued a reminder late on Thursday that pilots should follow standard procedures -- to maintain flight speed and angle -- if they thought their speed indicators were faulty.

Meteorological experts said the plane did cross a storm zone, but that it did not appear to pose a particular threat.

"Nothing would indicate (that the plane) hit a storm mass of exceptional intensity," Alain Ratier, deputy head of Meteo France told a news conference on Saturday.

MOUNTAINOUS SEABED

Search crews have failed to recover any wreckage so far and French and Brazilian aircrews are scouring a stretch of ocean some 1,100 km (680 miles) northeast of Brazil's coast where experts believe the plane might have come down.

Investigators are anxious to locate the plane's flight recorders are not optimistic they will be retrieved.

"This is what we are looking for in the middle of the Atlantic Ocean," Arslanian said, holding up a small, cylindrical canister which is attached to the flight recorders and designed to send homing signals for up to 30 days.

"We have absolutely no guarantee that it is still attached to the recorders. They can get detached," he said.

Shifting currents meant that in a worst case scenario searchers would have to be right above the beacon to hear it.

The search zone is a relatively uncharted patch of ocean which has deep ravines and a fine, muddy sediment.

France is sending a nuclear-powered submarine to try to locate the two flight recorders, which could be at a depth of anywhere between 864 and 4,000 metres (2,835-13,120 ft), said Laurent Kerleguer, the French navy's deputy head of hydrography.

(Writing by Crispian Balmer, Tim Hepher; Editing by Jon Hemming)