Graybeard:
OK, guys, maybe you can explain the overspeed warning had by the NW A330 into Japan recently? The static ports haven't been implicated, just the pitot probes.
I suspect it's not just the size of the bleed orifice compared to the main one, but also its alignment. If it is at right angle to the airstream, it will draw a vacuum, meaning that it is a much larger factor than mere size relationship.
Difficult to take NW incident as an example as very few details are actually available yet. It is missing most of the details: "large airspeed fluctuations, small altitude fluctuations, and an overspeed alert." That's all.
It looks like the fluctuation is due to sequential probes clogging/cleaning/clogging... then, at some point, over-pressure also. But from all other more detailed reports, when the probes are blocked for few minutes, the speed is always under-reported. And it is very difficult to know exactly where and how they were blocked as, once landed, no ice remains. The same issue is reported from laboratory test as it is difficult to re-create some unknow conditions in order to simulate and study this particular failure.
S~
Olivier