Originally Posted by
gums
So if we have the confusers not believing speed, or if they sense low speed, they forget about AoA protection? Does this work if the speed is zero or 1000 kts due to iced up pitots?
I can understand a WoW switch and 60 knots on the ground, but inflight???
Yeah, you aren't the only one who doesn't understand this bit of logic. Not sure if the fault is in the ADIRU logic or the stall-warning though - or maybe (I think the stall warning is not from ADIRU but higher level) both are "correct" for their inputs and outputs (eg. if the vanes don't work below 60kts maybe the ADIRU is "right" to send out no AOA value), but the overall result makes no sense.
It seems to be:
iAS valid, > 60kts - stall warning on AOA
iAS invalid, > 60kts - stall warning on AOA (but might be spurious)
iAS < 60kts - no stall warning, whether iAS valid or not
That last one seems all wrong - if iAS is valid and <60kts in a big jet then surely you are stalled
whatever the AOA vane says ? If iAS is
invalid <60kts, then a warning
might be spurious - but we run that risk if the speed is invalid but over 60kts, so why change at 60kts ?
It does look like a hole in the design (with the limited info we have at this point) - whether or not it is significant in the outcome in this case remains to be seen. Possibly it was irrecoverable anyway by the time this issue confused them.