Quest. for A320 techs - AoA tolerance

[MFALK]

What is the A320's Maintenance Manual tolerance value for AoA value discrepancy sensed by the ADRs, and how does this compare to tolerance values on other aircraft? Thanks.

[jetboy]

(I found this info in the Honeywell A320 ADIRS Line Maintenance document).There are three AOA sensors on the A320. Each
AOA sensor feeds into a separate ADIRU. Each AOA sensor contains two resolvers. Pin programming determines whether or not the ADIRU uses one of the two resolvers as a primary reference and the other resolver as a backup (UNIQUE) or whether it combines the two resolver signals (AVERAGE). My experience is that most airlines opted for the UNIQUE set up. Each ADIRU uses CROSS CHANNEL buses to compare the AOA signals of each of the three sensors. In order to perform the test, the de-icing status of all three sensors must be the same (ON or OFF). The test is performed during the take off phase and is determined to pass as long as the indicated AOA is less than or equal to 4 degrees. How this compares to other aircraft, I am not quite sure .But I do know that a good smack with an airbridge or a direct hit with a hose during an aircraft wash will destroy them. The first sign of a damaged AOA is usually a write up in the TECH LOG about errors with the GREEN DOT SPEED indication.

[MFALK]

Thanks for that info.

In fact an Airbus Bulletin states that even 0.3 degrees error in AoA determination can result in a 3 tonne discrepancy between FAC and FMGC weight computations, and hence different speeds. The same bulletin says that the max discrepancy for an acceptance flight is +/-5 knots for Green Dot speed in clean configuration.

There is an also an explantion how the 'voting' system works, and says that if one is out, it is disregarded, with no indication on the flight deck. Will the wrong ADIRS show up in the PFR? And how much must the difference be (during flight, not during the take-off check you mentioned) for an AoA signal to be voted out? Thanks again.