Baron cabin differential alarm

lancealotg

I seem to get this alarm on almost every flight.
I typically cruise at 24 to 25 thousand feet which is at or below the certified ceiling.
I also sometimes get this alarm when descending.

I set the control for 500 ft above my cruise altitude and set it for field elevation plus 500 when descending and have the rate knob at the 10 o'clock position resulting in about a 750 rate of change.

Is there a proper way to control the pressure system to prevent this alarm?

Voice of Reason

@lancealotg Reply from the developer for you...

The pressurization system is capable of maintaining a 12,500 ft cabin pressure (does not require oxygen for crew members by FAA rules) just barely up to 25,000ft. At that altitude, you might expect to see the warning as you approach the maximum differential. The setting on the cabin altitude goal selector is the minimum possible altitude attainable with the maximum allowable cabin differential. It's actually in the best interest of the pilot not to request this maximum differential pressure on every flight, since the number of cycles and differential pressure negatively affect the integrity of the airframe's pressure vessel. For instance, if you are flying at 10,500 ft, the aircraft can maintain sea level pressure in the cabin; however, this is completely unnecessary. The short version is to just give the pressurization controller a little extra headroom by selecting a higher cabin altitude whenever possible. I hope that helps!

lancealotg

Thanks for replying,

I have tried setting the cabin altitude higher by 500 feet then 1000 feet, but the differential alarm will persist.
Even on descent, the differential hand will stay pegged to over 3.9 giving me the alarm. This does not seem right.

The way I interpret the manual, the plane should only go to a max of 3.9 differential and not go over that (unless there is a problem with the planes internal valves). At that 3.9 max, the cabin altitude will then start to increase to keep the plane at a 3.9 max.

When the cable altitude reaches 12,500 or above, I should then get a cabin altitude alarm.

It seems there is something wrong with the coding of the differential system, allowing the plane to exceed the 3.9 maximum, thus giving me the differential alarm.

Voice of Reason

@lancealotg And another reply from the developer on this...

I did some testing with this today. The pressurization system is working correctly to my knowledge. When you exceed the maximum cabin differential pressure, the pressurization controller does not simply limit the maximum differential, but will "bump" (as the manual calls it) the pressure relief valve open with hysteresis to reduce cabin pressure before descending once again. I slightly adjusted the altitude goal animation to give more precise numbers (I doubt the unit in the real aircraft is this precise, given my experience owning GA aircraft). Don't forget that the marking on the face of the instrument also makes the setting subject to parallax effects. I also found the pressure differential needle to read about 0.1 PSI high, which has now been corrected, but this would not affect the warning annunciators.

Cruising at 25,000 ft, I was able to maintain a cabin altitude of 12,500 ft with a pressure differential of 3.674 PSI, which matched on all the needles. At 25,000 ft, the maximum pressure differential of 3.9 PSI was achieved with a cabin altitude of 11,800 ft, which is slightly better performance than advertised. I had found similar results on a previous investigation for another customer. Keep in mind that the cabin pressurization scale depicts pressure altitude, not adjusted cruising altitude. This means that the altitudes advertised will only be exact on a perfectly standard temperature and pressure day.

If you would like the new settings for the pressure differential needle of a more accurate reading, please change the following values in the "CabinDifferentialPressureNeedle" Component of AnalogBaron.xml. This file is located at: [YourCommunityFolder]\bksq-aircraft-analogbaron\SimObjects\Airplanes\bksq-aircraft-analogbaron\model.base\

MAX_VALUE 7 --> 9
END_DEG 285 --> 360

Good luck, and let me know if you have any more troubles!

lancealotg

Thank you for a very detailed explanation.

My main concern was that I was getting this alarm on at least 95% of my flights.
Hopefully those changes to the xml file and by using density altitude will reduce or eliminate this issue for me.

Thanks again for a very enjoyable product.
It has changed the way I fly.
I am always on the lookout for abnormal conditions when I fly.