Originally Posted by
rudderrudderrat
Hi DozyWannabe,
Sorry - I must be a bit dozy. I still don't understand.
The stall warning is triggered when measured Alpha exceeds some threshold. Alpha > X. The vanes are unreliable in airflow less than 60 kts. Therfore:
1) Inhibit when IAS <60 kts = No good for AF 447 scenarios.
2) Only Inhibit IF IAS <60 kts AND WoW, else Shout when Alpha > X
Why would 2) make a false stall warning on climb out more likely?
How exactly does (2) work ?
The issue is that when IAS < 60kts Alpha = NaN (or NCD or whatever invalid indication). This happens
before the SW computer.
So, is NaN > X or not ? That is the issue the SW logic has to decide.
You can't just fix the SW logic, in any meaningful way. The input data simply isn't there in this scenario.
You could maybe give the SW memory so it uses last-valid value, which would catch the 447 scenario - but that adds complexity and failure modes there.
Or you route raw AoA around the ADIRU for SW purposes - which is I think what the BUSS solution does (as a side effect of its main job) ?