The release of EASA emergency Airworthiness Directive 2014-0266-E on December 28 and a subsequent FAA Emergency AD were the the result of Nov. 5, 2014, in-flight incident aboard an Airbus A321, according to the French BEA. The aircraft was climbing on autopilot to FL310 about 15 minutes after takeoff from a European airport when the aircraft suddenly pitched nose down into a descent that reached 4,000 feet per minute. The flight crew was able to halt the descent at FL270 and continue safely to their destination at that altitude without injuries to any of the 109 passengers or crewmembers.

An investigation into the pitch down quickly focused on the aircraft’s attitude system technology after two of the three angle of attack (AoA) probes became blocked with ice. That caused the Airbus’s Alpha Protection Mode, which normally guards against an overspeed condition, to swing into action by pitching the aircraft down. The later Airworthiness Directive not only cautioned crews about the pitch-over possibility potential if the AoA probes iced up, but also explained the need to turn off at least two of the aircraft’s air data reference (ADR) units to regain control. In a worst-case scenario, a crew might be unable to halt the nose-down pitching movement, leading to a complete loss of control, the AD said.

The chain of events that led to the June 2009 loss of an Air France A330 over the south Atlantic began when ice blocked the pitot tubes on that aircraft.