Graybeard:
Pitot probes have a liquid drain (bleed) hole, whose air bypass has to be accounted for in the airspeed calcuation. Clog the drain, and pitot pressure rises, giving erroneous high airspeed. Indeed, per reading in this thread, some of the earlier Airbus pitot malfunctions were with poorly manufactured drain (bleed) holes.
Add more ice, and you clog the pitot head itself, and then pitot pressure will lock, or will decrease if there is any drain opening at all.
Hi,
I'm with Hyperveloce on this one. Considering the drain's hole dimension (I've got this detail somewhere) which is very small on Thales probes, an overspeed would be barely noticeable and certainly won't reach this 20-30 kts overspeed range that this simulation would imply (maybe only few kts at max). When drains are blocked, ice will build up much faster because turned into water by the probe heaters, then the pressure will be under reported.
S~
Olivier