A union at Air France has advised pilots to stop flying Airbus A330/A340 aircraft until the company replaces speed sensors that have become the focus of an investigation into the crash of a French airliner last week.

Air France said at the weekend it was speeding up the replacement of speed sensors, known as pitot tubes, on all its Airbus long-haul planes, but did not give any timeframe for the modifications.

The Alter union said its members should not take to the air in these planes until the changes had been made.

"Refuse any flight on a A330/A340 which have not modified at least two pitot sensors," the union said on its website. There are three pitot sensors on the A330 Airbus.

An Air France A330 en route from Rio de Janeiro and Paris crashed into the Atlantic last week, killing all 228 on board.

It was not immediately clear whether Air France pilots would heed the union's advice and whether this would have any impact on the company's operations.

Investigators have said there were "inconsistencies" with the speed readings prior to the crash, raising speculation the pitot tubes on the aircraft may have iced up, feeding wrong data into the cockpit which confused the pilots as they hit a storm.

The French air accident agency says it was too early to pinpoint any possible cause with the meagre clues so far.

Air France said at the weekend it noticed icing problems on its speed sensors in May 2008 and asked Airbus for a solution to reduce or overcome the difficulty.

Airbus responded by reaffirming existing operating procedures, according to Air France in a statement on Saturday.

Air France said tests had later convinced it that probes developed for another model would be more efficient and that it had decided to go ahead and start fitting them from April 27 without waiting for further testing proposed by the planemaker.

The A330 that plunged into the Atlantic had not yet been modified.  Airbus has declined to comment on the Air France statement.

The Alter union said the airline should have grounded all its A330 and A340 fleet until the pilot tubes had been changed. - Reuters