Airlines Replace Monitors After Air France Crash

A key part of the investigation relies on a burst of 24 automatic messages the plane sent during the last minutes of the flight. The signals showed the plane's autopilot was not on, officials said, but it was not clear if the autopilot had been switched off by the pilots or had stopped working due to conflicting airspeed readings.

The L-shaped metal Pitot tubes jut from the wing or fuselage of a plane, and are usually heated to prevent icing. The pressure of air entering the tubes lets internal sensors measure the speed and angle of flight. A malfunctioning tube could mislead computers controlling the plane to dangerously accelerate or decelerate.

Air France said it began replacing the tubes on its A330 and A340 jets in May after pilots reported several incidents of icing leading to a loss of airspeed data, and that it had already replaced the Pitots in smaller A320 jets after similar problems were reported.

"What we know is that other planes that have experienced incorrect airspeed indications have had the same Pitots. And airplanes with the new Pitot tubes have never had such problems," said Air France pilot Eric Derivry, a spokesman for the SNPL pilots union.