The European Aviation Safety Agency (EASA), prompted by a recent Airbus A330 incident, has issued an emergency airworthiness directive (AD) ordering A330 and A340 operators to update flight manuals with new procedures if multiple angle of attack (AOA) sensors become blocked.

The incident occurred while the A330 was climbing, and resulted in all three AOA sensors being blocked, says EASA.

According to the emergency AD, investigators suspect that conic plates installed on the sensors “might have contributed” to the incident.

The directive notes that both Goodrich and Thales AOA sensors could have conic plates installed.

The incident is “the first occurrence of three angle of attack sensors freezing over at the same time during climb” in the A330’s 23 million-plus flight hour history, Airbus notes.

“We are analyzing the incident and will share our findings proactively, immediately and widely within the aviation community,” the manufacturer adds.

In the interim, Airbus has issued new, temporary flight manual updates for both aircraft models. The updates cover emergency procedures for pilots to follow if multiple AOA probes become blocked.

The procedures vary based on the aircraft’s profile, but each includes ensuring that only one of the plane’s three Air Data Reference units is switched on.

“The blockage of two or three AOA probes at the same angle may cause the Alpha Prot of the normal law to activate,” EASA notes in the order.

“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 sidestick deflection, even in the full backward position,” the agency adds.