“...sometimes used to ponder, during my walk-rounds, on the pros and cons of locating Pitots 1 & 2 at precisely symmetrically-opposite positions on the fuselage (Pitot 3 being the odd one out). Then I would remind myself that the same applied to the AoA probes. It seemed to me that this might be a recipe for (roughly) simultaneous ice accretion of numbers 1 & 2."
Symmetrical position of AoA vanes is very common, the longitudinal position of A33/A34 is much further aft (aft of pax door#1) than e.g. the T7 (just below the flightdeck aft window).
Airbus don't want the surrounding skin to be heattreated so the base of the AoA sensor lacks a heating element this in contradiction to the T7.
....did the AoA sensors really iced up?
An A330 aeroplane, equipped with Angle of Attack (AoA) sensors with conic plates installed, 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 the subsequent analysis, it is suspected that these conic plates may have contributed to the event. Investigations are on-going 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 aeroplane that the flight crew may 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 aeroplane.
condition on Airbus A330 and A340 aeroplanes.
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 AD 2012-0236, making reference to Airbus SB A320-34-1521 for in-service modification. This requirement has now been removed with revision 1 of that AD.
To address this condition on A320 family aeroplanes, Airbus developed an “AOA Blocked” emergency procedure, published as a temporary revision (TR) of the Airplane Flight Manual (AFM), to ensure that flight crews, in case of AoA sensors blockage, apply the applicable emergency procedure.
For the reasons described above, this Emergency AD requires insertion into the AFM of the Airbus TR.
This AD is considered to be an interim measure and further AD action may follow.
Here it says AoA blockage due to in-service modification of conical plates. (no mention of icing here).
They removed the requirement of installing conical plates but NOT TO REMOVE the conical plates from factory delivered and in service modified aeroplanes.
Question: Will a max. 4° elevator down - due to activation of Hi AoA protect - command a 12° pitch ND?
Or will the Anti Pitch Up Compensation - blended in from M 0.65 to max 6° elevator down - had more effect on the 12° pitch down?
(New procedure states: DO NOT INCREASE SPEED !!)
@CONF: I have to say it again……..sometimes manual pitch trim can be your best friend!