Greg writes:
"What was most distracting; immediate decompression due to loss of
 airspeed indicator. IVP have a safety switch that dumps pressurization
 when speed is low to prevent landing with pressure."

I NEVER understood this one. Why  would you need such a thing? It is practically IMPOSSIBLE to taxi a IV-P when it is pressurized and it is damn difficult to land one with the deck pressure above ambient. Pressurized air enters the cabin through the sonic venturi which is essentially a 1/2" diameter hole that connects the engine deck pressure (between the turbos and the butterfly) to the cabin. There is no check valve so air will flow from the cabin into the engine if the pressure differential reverses. Even it there was a check valve, most IVs leak enough to bleed any differential pressure in seconds.

The airspeed switch should be used to lock out a gear retraction below 67 KIAS, that is it. The only time you may want to be sure that cabin pressure is dumped is during the takeoff roll. The rapid rise in deck pressure can overwhelm the outflow valve servo loop and  cause some minor fluctuations in the cabin pressure. Some newbie passengers find this alarming so  I forewarn them. I elected not to use the dump option on my plane. With over a thousand landings logged, I have never had a pressurized cabin on rollout, or on short final for that matter. If you must have a cabin pressure dump then hook it to the gear switch. Greg's experience shows that connecting the dump function to the airspeed is a very bad idea.

Regards
Brent Regan