The European Aviation Safety Agency recently published an airworthiness directive (AD) for the flight manuals of the Airbus A320, A330 and A340 series to address an undesirable nose-down movement that could occur should an angle-of-attack (AOA) probe on the aircraft become blocked. The AD was issued as the result of a benign occurrence reported on an A321. The FAA followed up with emergency AD 2014-25-52.

“When the alpha protection mode is activated due to blocked AOA probes, the flight control laws order a continuous nose-down pitch that, in a worst-case scenario, cannot be stopped with backward sidestick inputs, even in the full aft position,” stated EASA.

The Airbus-developed interim actions that became effective December 11 begin with keeping one air data reference on, while turning off the other two. However, there is still a risk of erroneous stall warnings appearing on the speed display, EASA noted. For the A330/A340 models, on which there may still be a false stall warning, Airbus suggests “using the flight path vector” in the recovery process.