UPDATE 1-FACTBOX-Attention centres on Air France speed sensors

(Adds comment by Emirates and Etihad Airways airlines)

June 10 (Reuters) - Air accident investigators have said an Air France Airbus A330 was registering "inconsistent" speed readings before it crashed into the Atlantic Ocean last week.

Air France (AIRF.PA) has since said it noticed temporary loss of air speed data on previous Airbus flights due to icing up of the speed sensors, or pitot tubes.

Aviation experts and pilots' unions have asked whether the same thing might have happened on the doomed Airbus A330 as the pilots tried to navigate equatorial thunderstorms.

Here are details and background on the pitot tube:

CONTRIBUTING FACTOR?

Pitot tubes on aircraft are typically heated to prevent them becoming clogged with ice. Investigators are looking into whether this mechanism failed, but the head of France's air accident agency has said it is too soon to say if problems with the sensors were in any way responsible for the crash.

A French pilots' union, Alter, said on Tuesday that "there is a real risk of losing control of an Airbus" in the event of a pitot tube malfunction, but added that it was drawing no conclusions on the cause of flight 447's crash.

Another pilots' union, SNLP, said frozen pitot tubes could not be the sole reason for the disaster.

Widely used to gauge the speed of aircraft, pitot tubes are also used to measure wind and gas speed for industrial purposes.

Air France has said all its flights using long-haul Airbus (EAD.PA) jets will be equipped immediately with new speed sensors, a pilot's union said on Tuesday [ID:nL918170].

CAUSE OF PREVIOUS CRASHES?

Blocked speed sensors have been blamed for contributing to aircraft crashes in the past.

In 1996, a report into the crash of a Boeing 757 airliner off the Dominican Republic blamed a faulty reading by the pitot tube -- which was blocked by dirt or insect remains -- for the disaster, alongside pilot error.