Hi All,

Today I was up flying and figuring out the pressurization system.  Things like if the annunciator panel / warning horn would sound if the "dump" switch was in the on (don't pressurize position).

As I climbed through 11,000' the horn and annunciator panel lit up.  I could see that the system wasn't pressurized as the gauge indicated the cabin pressure at pretty much the same as our altitude (we were at 11k and the cabin showed 10k).   The dial was set to the 1000' field elevation.    I flicked the dump switch and the cabin immediately began to pressurize (I could feel it in my ears almost immediately after flicking the switch).  I then climbed to 14000' to see how the system would react (Power setting 28" and 2300RPM).   At 14,000' the pressurization horn went off again as the cabin pressure got to 10,000' again.  I realized that I forgot to change the dial to my cruising altitude of 14,000', so I then dialed up 14000', thinking that the pressurization system would then pressurize to that new altitude --- but it didn't.  It just stayed at a cabin pressure of 10k.

I have a couple questions... 

1)  I presume the cabin pressurization should be set to my cruise altitude BEFORE I get there as turning the dial to my cruising altitude after I get there doesn't seem to work... is this right? That would be the normal thing to do but that's not why it's not pressurizing.  I think most IV's can maintain pressure at 29"/2500 and some can do better.  If you can't maintain pressure at that setting, you have a leak in the cabin somewhere or your outflow valve is stuck (another form of leak).

2)  People have told me that I should set the pressurization 1000' above my actual cruising altitude and field elevation on landing... is this right?  Whats the logic here?  1000' above landing is so that you don't land with a pressure differential, although in practice it's hard to land with a high enough power setting to have a pressure differential.   I haven't heard of setting you target altitude above your cruising altitude.

Thanks,

Dico