Pitot freezing: over/underestimation
I see GB, indeed, with both the Pitot tube ram air and the drain blocked, a machmeter should work like an altimeter, largely overestimating the airspeed if altitude increases (seems in the order of +40kts/+1000ft @FL350). But if altitude remains constant, it can't be an overestimation ?
Jeff
PS) following an accident wich began by Pitots freezing, obstructed or polluted Pitot drains were found on a large fraction (~20%) of the French fleet of Mirage 2000 (with a high probability of occurrence, ~70%, in humid/hot areas). the quality of the manufacturing was also a problem for a fraction of them.