Colyn Case asked “… long range profiles and noticing that a lot of the interesting range is below

28" MP.  I've heard this is the least that will keep you pressurized at altitude.

 

Is this really true?”

I begin to loose pressurization below 25” MP.  I did not do anything special to tighten up the pressure vessel other than in the manual: pressurize it to 5” , look for leaks with smoke and seal with RTV silicone.  

I never cruise at this setting, this is only used in descents.  I usually cruise in the Flight levels 240 and 250. 

25CL IVP with TSIO 550 E, 780 hours

 

Carl Cadwell