bubbers44;
but if he climbed for whatever his reason with trapped pitot pressure and reducing static pressure he may have gotten an overspeed warning that caused him to pull up into a stall.
Yes I know. I make that observation in my post. I've had this occur in a B767 and that is precisely what happened...the airspeed increased beyond the VMO, (didn't get the Overspeed warning though) but in our case we ignored it because we had the standby AS to help us guess which one had the correct reading.
My point in this part of the argument is that the speed increase in a thousand foot increase at the beginning of the pitch-up isn't dramatic...it isn't in the order of "50kts", say...and it isn't much more in a 3000ft increase...it isn't large enough to warrant a pitch > 10deg to reduce speed.
3holelover;
What is the expected result from a gradual blockage of the drain hole alone?
It depends upon whether the tube downstream of the drain hole is also plugged due rain unable to drain fast enough from the pitot tube. If the tube is blocked, the effect is the same as if both the tube and the drain hole is blocked and the airspeed would drop. If the blockage was due to water (flight through heavy rain), the speed could fluctate between actual and lower indications and would do so in relation to the changing amount of blockage. If the drain hole itself is plugged but the tube itself is clear, then I think that there is no effect on the sensed total pressure and the airspeed would be accurate.
All this is largely from the A300-600 FCOM information on "Abnormal Procedures - PITOT PROBE DESIGN, (posted by Chris Scott or gums which I can no longer find on the previous threads) - Thank you Chris for finding Tubby Linton's post.