Hamburg  - Amid fears that last week's fatal Air France crash may have been caused by faulty air-speed sensors, the European Aviation Safety Agency (EASA) cautioned airline pilots Tuesday that they must rely on other flight data if the devices play up.

The advisory from the agency, which is based in Cologne, Germany, went to all operators of intercontinental flights.

Sources told the German Press Agency dpa the advisory was prompted by analyses so far of the mid-Atlantic crash in which 228 people were killed when an Airbus A330 plane fell into the ocean.

EASA told pilots that even when air-speed sensors fail, there are established procedures to keep planes flying safely, provided crews stick to the operating instructions. EASA has been responsible since 2003 for safety approvals of planes flying from Europe.

An EASA spokesman, Daniel Hoeltgen, said the cause of the crash was not yet known. "But we have to consider all possible causes," he said.

French transport officials say the inquiry is focussing on whether the sensors malfunctioned, which might have tricked the pilot into flying too fast or too slow.

Too low a speed would cause a plane to "stall" or fall out of the sky. Too high a speed could push it near the speed of sound and damage the plane's outer metal skin. Air France has said it is replacing speed monitors on board its Airbus planes.

Hoeltgen stressed the advisory was not yet a directive notice, but said EASA was working urgently on drafting a directive.(dpa)