A320: Tricky angle of attack question

[cambion]

If you want to see your angle of attack, you have to type AOA and AOA3 in the Alpha Parameters. Type AOA and you get AOA1 and AOA2. The screen says the info comes from ADR 1 and 2. Up to this point everything is normal. The weird (at least for me) things happen with the AOA3.

-For the AOA3 the info comes from FWC in some airplanes and from DMC in others. Weird.

-In some airplanes the value of the AOA3 is coherent with AOA1 and AOA2, but in others, the value of AOA3 is much larger than AOA1 and AOA2. Around double, and for the whole flight. We have a mixed fleet of A319/320/321 and a broad range of MSN.

Example:

AOA1 (ADR1)......2,7deg
AOA2 (ADR2)......2,8deg
AOA3 (DMC1).....5,4deg

Any light on this subject?

Thanks

[A33Zab]

@ cambion:

AOA1 (ADR1)......2,7deg
AOA2 (ADR2)......2,8deg
AOA3 (DMC1).....5,4deg

IIRC it has to do with the mod (EIS2) status.

For pre-mod all those AOA values are Indicated AOA values.
For the post-mod the AOA3 (DMC) is the sum of Indicated AOA value(ADR) and the Corrected AOA from the IRS.
That is why the result is, in general, a factor of 2.

Reason: to have the (median) Corrected AOA stored on DFDR because in EIS2 this will be the source for BUSS.