Originally Posted by Chris Scott
There seems to have been wide agreement here for a day or two that − in level flight, right at the beginning of this event − whichever ASIs were showing erroneous readings are more likely to have been over-reading the actual IAS/CAS, than under-reading it.
Chris;
Not me. I feel it is not impossible but somewhat unlikely. The UAS procedure mentions the possibility of an overspeed warning, but I think that is primarily to cover the case of an airplane taking with probes and/or ports blanked off. On page 60 Sensor Validation points to the possibility of pitot overpressure due to drain blockage, but adds that he doesn’t know by which percentage. Until someone comes up with that information, I’m inclined to think that the effect is quite small.
Where you had a difficulty with the translation, the french version reads:
Les anomalies de vitesses peuvent se caractériser par deux signatures distinctes :
- chutes intermittentes (pics),
- chute suivie d’un palier (période continue).
Originally Posted by Chris Scott
These are often combined with (phase-advanced) stall warnings caused by rapid AoA fluctuations, presumably in what many pilots would call "severe" turbulence.
To my knowledge, stall warnings are not phase advanced (stickpushers sometimes are). Based on the cL-AoA data obtained from the QF72 event (the whole manoeuvre was between Mach=0,808 and 0,818), at a typical cruise turbulence penetration condition of Mach=0,8; FL 350; 200t the margin to the onset of stall warning at AoA=4,2 degrees permits a loadfactor of 1,35 g.
HN39
see image here:
https://docs.google.com/leaf?id=0B0C...NjRhZGMw&hl=fr