Michael wrote, "I have never seen an alternate static source on a light GA
airplane that shut the external static source off. ..."

Several posts in this thread reminded me of an incident that happened to me
several years ago a few weeks before I got my PP certificate. I intended to
fly from Front Range Airport (FTG) in Colorado (where I was then based) to
Centennial (APA) to meet my instructor. I'd made this short solo flight many
times before.

Before taking off, I called Unicom and got the altimeter setting: 30.10. I
set the altimeter and observed that it read 5495 feet. Field elevation is
5500 feet so that checked.

I performed a normal takeoff. Airspeed alive, rotate at 55 KIAS, climb out
at 80 KIAS.

A few seconds later I glanced at the altimeter and saw it still read 5500
feet! It had always read about 6000 feet at this point. Did I forget to set
the altimeter? I called Unicom and requested the altimeter setting. It was
still 30.10. I verified the setting: 30.10. I leveled off at what looked
like pattern altitude -- 6500 feet. The altimeter still read 5500 feet and
the ASI still read 80 KIAS. It should have been about 120 KIAS by now.

I knew I couldn't possibly have a blocked static port -- the 182 has two --
because no one else flew the plane and I hadn't washed it or performed any
maintenance and it had been in the hangar since the last flight when
everything worked perfectly and I checked both ports during preflight and
they were clear.

Even though I _knew_ the static ports couldn't possibly be obstructed, I
pulled the knob to open the alternate static source.

The ASI immediately showed 120 KIAS and the altimeter immediately showed
6800 feet.

I completed the flight to APA without further incident.

Once on the ground, I told my instructor about the problem I'd had. We
investigated and soon found the problem.

The alternate static source knob on the 182Q is normally in. To select the
alternate static source -- a short tube that opens to cabin pressure -- you
pull the knob fully out. During preflight, as I had done many times before,
I pulled the alternate static knob out then pushed it back in to verify
normal static source was selected.

This time, however, without my noticing it, the little plastic trim piece
that surrounds the knob, which had been loose since I bought the plane, fell
down a fraction of an inch when I pulled the knob out. When I pushed it back
in, the knob contacted the trim piece and stopped about half way between
normal static and alternate static. That half way position turned out to be
an undocumented Static Blocked position!

I think it's ironic and amusing that the very device that was intended to
prevent a blocked static line actually caused the blockage.

Jon