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Old 24th May 2011, 21:09
  #2294 (permalink)  
Turbine D
Join Date: Dec 2010
Location: Middle America
Age: 81
Posts: 1,162

In fact, in normal flight, all the sensors are already not displaying the same data by a certain margin due to their airframe location: an aircraft is almost never flying in a perfect symetrical attitude and this will cause some noticeable variation between the various sensed pressures. This is also the main reason why a clean probe system would very very unlikely be clogged (in flight) at exactly the same rate and at exactly the same time.
I am not sure how to reconcile the above quote with this quote extracted from the EASA AD No. 210-0271 dated 22 December 2010:

It has been identified that, after such an event, if two airspeed sources become similar while still erroneous, the flight guidance computers will:
-Display the FD bars again, and
-Enable AP and AT re-engagement.
Doesn't that say that that speed sensors can go from similar to dissimilar and then back to similar? Similiar at the same time as in normal cruise flight, dissimilar at the same time causing AP & AT disconnect and removal of FD bars, and then similiar again at the same time but giving wrong speed data, e.g., somehow clogged in a similiar fashion.
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