Originally Posted by
Speedwinner
And if it has no buss system? I would switch off a reliable alt indication…
In non BUSS Aircraft the stall warning was processed through ADR. So even with all ADRs unreliable it was recommended to keep one ADR on for stall warning. This was modified later by processing the stall warning through IRs. So when all three ADRs are switched off to get the BUSS the stall warning is still available. Even with BUSS equipped aircraft though stall warning is available through IR, when above FL250 you are still asked to keep one ADR on. That is for when you descend below 250 that lone ADR helps you check whether you have recovered valid speed. If it's still not OK then switch it off and change to BUSS. The ADR check procedure is only meant for speed indication and not for altitude.