A French investigator says speed sensors were a factor but were not the cause of the crash of Air France flight 447.

Alain Bouillard, leading the investigation into the June 1 crash for the French accident investigation agency BEA, says the sensors, called Pitot tubes, were not the only factor.

He says "it is an element but not the cause."

One of the automatic messages emitted by the plane indicates it was receiving incorrect speed information from the external monitoring instruments, which could destabilize the plane's control systems. Experts have suggested those external instruments might have iced over.

All 228 people aboard the plane were killed when it plunged into the ocean en route from Rio de Janeiro to Paris.