Pressurization and Oxygen systems

KRoy7

Not having had prior experience with pressurization and oxygen systems, I want to confirm my understanding of the Duke's systems. I have read these sections of the documentation multiple times, and am feeling that I need to confirm the following:

Reason that the CABIN ALT outer dial on the rightmost gauge goes up beyond the "desired" cabin alt range is because there could be a leak or depressurization.
Oxygen is only used in the event of the pressurization system not functioning properly, leak, blown window, etc.
pressure differential is not necessarily for targeting a specific diff pressure, but more as an additional indicator that could show either that there is a leak / depressurization, or to indicate that the dP is high possibly indicating that the CABIN ALT setting cannot be achieved at the altitude being flown
Importance of setting the CABIN ALT to the destination field alt, is to avoid a sudden pressurization change when opening the door at the destination. BUT - this same control is used for setting the targeted CABIN ALT desired during cruise? So it's used for two purposes?
Main reason for the CABIN CLIMB gauge is to help with setting the desired cabin climb rate using the RATE/INCR knob; but ALSO as an indication of potential discomfort to passengers if the pressurization system is not able to hold the CABIN CLIMB down to a comfortable rate, which would be <= to 500-600 fpm?

Thanks for the confirmations and any comments, this will be really helpful for my confidence in how I manage these things.

xender

Im not an expert but I do know a few things:

Regarding point 1: That happens for any reason that prevents the cabin from being pressurized. A leak is one of these reasons, that's true, but also remember that the engines are used to pressurize the cabin. In the piston duke if you lower your throttles too much, the cabin will lose pressure slowly and you can end up with a depressurized cabin.

Point 2) Per FAA rules, it goes like this. Keep in mind that these altitudes are cabin altitude
Sea Level to 12,500' - No oxygen required
12,501' to 14,000' - Required by the required crew if over 30 minutes at this altitude
14,001' to 15,000' - Required to be provided and used by the required flight crew
15,001' to 25,000' - Must be provided for every occupant

Point 3: Pressure differential shows you the difference between the outside and the inside. If there's a leak, the pressure will equalize and the pressure differential will begin to get lower until they're the same.

Point 4: That's correct.

Point 5: That's correct too. Bear in mind that if your cabin altitude is climbing/descending faster than the airplane, your pressure differential will increase. During your climb and descent you may need to adjust the rate to keep the pressure differential within limits.

Sorry for my bad English, hopefully everything is clear

Black Square

Yes, you are generally correct on all points. My only small additions are as follows:

The scale is also just larger than the maximum desirable pressurization altitude because the same gauges are used in many different aircraft with different markings.
The FAA oxygen requirements above pertain to cabin altitude, while a different set of rules pertains to the required type of oxygen system on board that an airplane must have to legally fly at higher pressurization altitudes. The oxygen would be used in one of three scenarios:

Loss of pressurization
Cabin altitude is above the FAA requirements listed above (this can happen easily in the Duke, because the maximum differential pressure is not nearly as high as similar aircraft that fly at the same altitudes.
To save a pressurization cycle on the airplane. Most pressurized airplanes have a limited lifespan based on the number of times they are pressurized. On some airframes, you only count a pressurization cycle towards this limit, not every single flight cycle.

Related to the point above, the differential pressure is also a measurement of how much stress your are placing on the aircraft's windows, door seals, and pressure vessel.
In most pressurized aircraft, the pressurization dump valve is opened when the weight on wheels switch is triggered, so you feel a "bump" in cabin pressure as soon as the wheels hit the ground. If everything is working correctly (it might not be in my aircraft), the cabin should long be depressurized by the time you go to open the door.
The cabin climb rate needle should also be your primary instrument for detecting pressurization failures, not the differential pressure. If you're in level cruise flight, but the needle is indicating a slight climb, it's possible that you have a small leak, like a compromised door seal, or a stuck valve, which are also possible in my aircraft.

Hope that helps! Great questions.

KRoy7

REALLY appreciate both of you taking the time to articulate these details. The Black Square aircraft have inspired me to take my understanding to the next level, before I start to activate failures. Thank You!