Originally Posted by
akaSylvia
Thanks for the explanations, especially the snowless photograph!
Bizarrely, just yesterday I spent an hour explaining to someone about the Aeroperú 603 crash and how a partial blockage is harder to spot than a complete one. But I thought that in that case, the readings are too low while climbing and too high while descending which doesn't seem to map with MVP3.
Regarding automated heating: that it isn't at all clear that the pilots didn't turn the heat on (or that it wasn't automated), just that they didn't manage to diagnose the issue in the first minutes of the flight.
A blocked pitot will cause the airspeed indicator to work a bit like an altimeter. As you climb the ASI progressively reads higher and as you descend it reads lower.
I once discovered I had an iced pitot on a Pitts Special as I was climbing out (caused by water in the dynamic pressure lines rather than flying through icing conditions). The whistling in the wires was enough speed information to be able to continue the aerobatic sortie and once that was completed the ice had cleared and the ASI was working normally for landing. Being solidly VMC helped of course.