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DATE: December 17, 2012
AD #: 2012-26-51Emergency airworthiness directive (AD) 2012-26-51 is sent to owners and operators of
Airbus Model A318, A319, A320, and A321 series airplanes.Background
The European Aviation Safety Agency (EASA), which is the Technical Agent for the Member States of the European Community, has issued EASA Emergency Airworthiness Directive 2012-0264-E, dated December 17, 2012 (referred to after this as the Mandatory Continuing Airworthiness Information or “the MCAI”), to correct an unsafe condition for the specified products.EASA has advised that an Airbus Model A330 airplane equipped with Angle of Attack (AoA) sensors installed with conic plates recently experienced blockage of all sensors during climb, leading to autopilot disconnection and activation of the alpha protection (Alpha Prot) when Mach number was increased. Based on the results of subsequent analysis, it is suspected that these conic plates may have contributed to the event. Investigations are ongoing to determine what caused the blockage of these AoA sensors.
Blockage of two or three AoA sensors at the same angle may cause the Alpha Prot of the
normal law to activate. Under normal flight conditions (in normal law), if the Alpha Prot activates and Mach number increases, the flight control laws order a pitch down of the airplane that the flight crew might not be able to counteract with a side stick deflection, even in the full backward position.This condition, if not corrected, could result in reduced control of the airplane. EASA also issued Emergency AD 2012-0258-E, dated December 4, 2012, for Airbus Model A330 and A340 airplanes to require an amendment of the AFM to ensure that flight crews apply the applicable emergency procedure.
AoA sensor conic plates of similar design are also installed on Model A320 series airplanes. Installation of these AoA sensor conic plates was required for Model A318, A319, A320, and A321 series airplanes by EASA AD 2012-0236, dated November 9, 2012 (corrected November 12, 2012).
Subsequently, EASA issued AD 2012-0236R1, dated December 17, 2012, to remove the requirement to install AoA sensor conic plates.
