Airworthiness Directives; Airbus Airplanes

We are adopting a new airworthiness directive (AD) for all Airbus Model A318, A319, A320, and A321 series airplanes. This emergency AD was sent previously to all known U.S. owners and operators of these airplanes. This AD requires revising the airplane flight manual to advise the flightcrew of emergency procedures for abnormal Alpha Protection (Alpha Prot). This AD was prompted by a report of Angle of Attack (AoA) probes jamming on an in-service Airbus Model A321 airplane. Jamming of the two AoA probes during climb is attributed to water freezing under the AoA vane slinger, and led to activation of the Alpha Prot while the Mach number increased, which resulted in an airplane pitch down per design. We are issuing this AD to ensure that the flightcrew has procedures to counteract the pitch down order due to abnormal activation of the Alpha Prot. An abnormal Alpha Prot, if not corrected, could result in loss of control of the airplane.