Have to make a comment on this one, and will not continue much as I did on AF447 thread.
Anyone here that has had the aero probes freeze/quit should have observations such as mine. If the AP was trying to obtain a commanded speed or pitch or....., then you can see the beginning of the accident when the air data went tits up.
I had the static ports freeze up one day due to simple electrical failure of the heater. So descending to the approach fix the speed went up but the altimiter remained at whatever altitude the ports froze. AHA! I had not changed the pitch attitude, and furthermore I had an inertial flight path marker that remained where it was when the ports froze. Big deal, right? Continued descent and looked at radar altimiter. Also intercepted the ILS glide path from above once the needle came off the bottom of the indicator. Ports came clear a few thousand feet AGL, altimiter came back and landed.
I have to iterate some lessons rrom AF447 and other cases where the air data or other data goes bonkers. Turn off the AP!. Maintain attitude and power that existed when crazy things happened. Don't do something! Just sit there!