Airbus Sensor Challenges Force Mandate Reversal

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Perhaps obscured by Monday's emergency order requiring Airbus narrowbody operators to adopt new flight crew procedures for handling multiple blocked angle of attack (AOA) sensors was a revised EASA AD that addresses the challenge directly. 

First, some background. Research into ways to improve AOA sensor reliability led Airbus to develop a new, conic plate meant to replace flat plates and help mitigate blockage caused by ice crystal formation. Airbus recommended earlier this year that the conic plates be installed on both its narrowbodies and A330/A340 fleets as part of a broader AOA sensor replacement program. 

Then came word of the A330 incident, which prompted EASA to issue an emergency AD two weeks ago covering the A330s and A340, ordering adoption of new emergency procedures. Monday's emergency directive--quickly matched by FAA--did the same for the narrowbodies. 

There are at least two major differences between the two situations. One, the narrowbody fleet hasn't experienced an in-service, multiple AOA sensor blockage attributed to conic plates. (This could explain why the A330/A340 directive came first.) Two, EASA mandated installation of the conic plates on the narrowbodies, via AD 2012-0236 issued November 9. (The A330 multiple-sensor blockage incident occurred shortly after.) There's been no such mandate for the long-range aircraft.

All of which brings us back to Monday's other Airbus directive (.pdf). EASA issued a revised version of AD 2012-0236, removing the requirement to replace flat plates with the new conic plates, but maintaining other requirements to replace certain Thales AOA sensors.

Interestingly, the revised directive does not require removal of conic plates--it only deletes the requirement to install them. EASA hasn't ordered removal of conic plates from A330 or A340 AOA sensors, either.

One gets the feeling this may be just getting started.

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