Actualy one of my ASI incidents (had the bug one too) was caused by the
pitot cover. Preflighted the Warrior that had sat outside during the
previous nights thunder storm and removed the Pitot cover from the
underwing Pitot/Static. Actually the ASI came up just fine on take off
but he altimeter remained at field elevation and the VSI showed Zero
climb. At about 500 feet the VSI jumped and the Altimeter jumped about
200 feet up and the ASI jumped about 5 kts as well. after that the VSI
would jump about every 200 feet. I think I was giving a Flight Review
at the time so figured it was a good time to talk about attitude
flying. We did about 3 take offs and landings and after that everything
worked fine. I figured that the storm the night before had blown water
into there Pitot/Static cover and it had puddled in the bottom of the
cover and worked its way into the static System. Once we gained enough
altitude the pressure difference was great enough to force a bubble of
air through the static tube. After doing this a few times the static
line cleared itself.

Brian
CFIIG/ASEL

wrote:
Been there, done that. Likewise a bug in the pitot tube. In my case,
the ASI seemed to come up normally as I accelerated, then started to
gyrate wildly when I lifted off.

I made an uneventful landing - without difficulty, as I recall.
Cleaned out the remains of the bug with some safety wire and continued
on my way.

Since then I have been careful to put a cover on the pitot tube as part
of the after flight routine.

David Johnson