Hi
Originally Posted by
PA 18 151
If once the aircraft had validated the sensor data, it could have legitimately reverted to normal law, it could then have applied AoA protections and all on board saved.
So why is this not programmed to happen?
I think you misinterpreted what "valid speed" means. When the BEA writes "The speeds became valid again", it means the speeds were no longer below 60kt (for AoA stall warning) or below 30kt (for speed itself).
A
valid speed (system speaking) is not by definition a
correct speed (i.e. real).
The system cannot know if the sensed speed, after the pitot failure/icing, is back to correct values. In fact in some cases, speeds may be valid (above 60kt), consistent (3 equal values, or at last 2 equal values, the third being voted out) but not correct.
It's only the discrepency in speeds (from 3 sensors) that make the system decide "We got a problem". Unless you can confirm the correct speed by other means, it's safer IMO that the system let the crew decide. That needs the crew to be trained for such situations, and the SOP to be OK.
For the system to be able to decide, by itself, that the speeds are back to correct values, it would need to compare the ADR speeds with other sources. Perhaps the INU/GPS may be a source, here, in combination with the altitude (pression), the temperature and the wind speed/direction. If you have all of them, I suppose it's just maths (which a computer can do, and quickly).
The wind speed will be a problem, to me. How do you know it ?