The European Aviation Safety Agency issued an emergency airworthiness directive December 4 for the angle of attack (AOA) probes of both the Airbus A330 and A340. The AD, which became effective December 6, results from an incident in which an A330 in the climb experienced a blockage of all AOA probes, leading to autopilot disconnection and activation of the alpha (angle of attack) protection system when Mach number increased.
“Analysis showed this aircraft was equipped with AOA probes having conic plates, and it is suspected that these plates might have contributed to the event,” said the AD. “The AOA conic plates can also be installed on A340s.” According to the AD, this means that as Mach number increases, the flight control laws order a pitch down of the aircraft that the flight crew may not be able to counteract even with full aft deflection of a sidestick.
The AD–considered an interim measure–requires that the airplane flight manual be amended to ensure that crews apply the applicable emergency procedure in case of blocked AOA probes.