On Mon, 19 Apr 2004 10:05:58 -0400, Peter R.
wrote

What model C172?

Last year I flew several flights in a C172SP in rainy weather and noted the
same behavior you did. After speaking with a few pilots more knowledgeable
than I, I learned that this issue is commonly caused by the aircraft's
single static port becoming temporarily blocked by streaming water. For me,
engaging the alternate air was SOP during wet weather.

Greetings,

I seem to recall checking two static ports in my 172SP - one just aft
of the cowling on the left side, and one aft of the door, left side.
Since it's got two holes, are they calling this a single port because
they plumb to the same line inside, or has an additional port been
added? Would blocking one of the two (since the line itself is still
vented to the outside) cause this, or would a blockage have to be
forward of the forward static port (where the lines merge) to cause a
problem?

Random related question, is there some reason why are both ports on
the same side of the aircraft?