The U.S. Federal Aviation Administration has issued a preliminary Airworthiness Directive (AD) for 318 Boeing 767 airplanes.

This AD covers the aileron control override system; bearings in the units were found corroded and seized. All 318 control units and their bearings must be replaced within the next 18 months by units with corrosion-resistant bearings.

An aileron override system is a safety mechanism and does not come into play during normal operation. It is there in the event that the pilot's control system jams. If that happens, then the override system works to stabilize the airplane.

However, if the bearings have corroded and seized, as was found, then the override system will not work and the aircraft will experience, "reduced lateral controllability."

This is the 767's second bearing-related Airworthiness Directive in 2002. In February, the FAA issued an Emergency Airworthiness Directive covering bearing failures in the wing flap system.