Hi JD_EE,
Originally Posted by JD_EE
we've had two explanations doing the rounds - one, that the stall warning is inhibited by a software setting and the other is that once the airspeed has fallen that low that the AoA vane no longer functions.
There is only one single and simple explanation:
If no alpha_probe real failure is declared and no particular phase inhibition is declared:
1) - Stall Warning alarm is working provided that at least one ADR_alpha_channel is valid. (e.g. turning OFF all ADRs imply that Stall Warning alarm is totally lost).
2) - ADR_alpha_channel is valid provided that its own ADR_airspeed_channel is > 60 kt.
Consequently, if all three ADR_airspeed_channels are < 60 kt => case 1) Stall Warning alarm is lost.
But, this may become circular:
If alpha increases and is reaching a very high level, pitot_probes starts to under-read airspeed (due to angle of airflow related to ram tube orientation). At one point, alpha can be so high that airspeed is falling under 60 kt, causing alpha_probes to display NCD (invalid) values, causing the complete loss of Stall Warning alarm.
Consequently, the measured airspeed could be < 60 kt while aircraft is actually flying at 100+ kt but at very high alpha. Hence, high alpha will cause invalid alpha and Stall warning alarm will drop off at much higher airspeed than designed.