Recently, an Airbus A330 aeroplane equipped with Angle of Attack (AoA)sensors with conic plates installed, experienced blockage of all sensors duringclimb, leading to autopilot disconnection and activation of the alpha protection(Alpha Prot) when Mach number was increased.
Based on the results of the subsequent analysis, it is suspected that theseconic plates may have contributed to the event.
Investigations are on-going todetermine what caused the blockage of these AoA sensors.Blockage of two or three AoA sensors at the same angle may cause the AlphaProt of the normal law to activate.
Under normal flight conditions (in normallaw), if the Alpha Prot activates and Mach number increases, the flight controllaws order a pitch down of the aeroplane that the flight crew may be unable tocounteract with a side stick deflection, even in the full backward position.
This condition, if not corrected, could result in reduced control of the aeroplane.
AoA conic plates of similar design are also installed on A320 family aeroplanes,and installation of these AoA sensor conic plates was required by EASA AD2012-0236, making reference to Airbus Service Bulletin (SB) A320-34-1521 forin-service modification.
That requirement was deleted by EASA AD 2012-0236R1.To address this potential unsafe condition on A320 family aeroplanes, Airbusdeveloped an “AOA Blocked” emergency procedure, published as a temporaryrevision (TR) of the Airplane Flight Manual (AFM), to ensure that flight crews, incase of AoA sensors blockage, apply the applicable emergency procedure.
Consequently, EASA issued Emergency AD 2012-0264-E to requireamendment of the AFM by incorporating the Airbus TR.
Since that AD was issued, Airbus published approved instructions to re-installAoA sensor flat plates on A320 family aeroplanes.
For the reasons described above, this AD retains the requirements of EASA AD2012-0264-E which is superseded, and requires installation of AoA sensor flatplates, after which the AFM operational procedure can be removed.