Cabin DIFF HI warning

[matpietsch]

Hi,

I am pretty sure all my switches were set up correctly but I got a Cabin Diff Hi warning. Somebody has advice or is this maybe a bug?

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[jarek]

Notice position of your Bleed Air Valves (2nd picture) - they must be Open to let the air to flow to the cabin, pressurize it and then be gradually released by outflow valve.
You seem to set them in ENVIR OFF that only supplies vacuum and air for pneumatic system.

[matpietsch]

Unfortunately they were open. I checked this at least 10 times. You could see the cabin react for a few moments (lowering altitude) but then the needle went back to the middle position. I even tried to dump the cabin to get rid of the excess pressure. That also did not work.

[Raptor]

What is the plane altitude? You are asking the press system for a 9k altitude to fly over 30,000 but is only pressurizing to something like 5k if I see correctly. Post a picture of your oxygen valves and gauge (under the copilot yoke)

[matpietsch]

At that point FL300 but the failure began during the climb already. At around FL240 I think.

I am not able to provide further pictures unfortunately, as the flight is closed since yesterday.

[Raptor]

Next time look at the Oxy gauge and make sure you have enough oxygen for the flight

[jarek]

What was your origin airport for this flight?

[matpietsch]

Provo Utah

KPVU
Elevation around 4500ft.

[jarek]

Thanks, I will verify this scenario later today.

[matpietsch]

Appreciate your efforts!

If you are on it: can you fly in there too? Rwy13 ILS VNAV did send me on a 5500ft/ min dive in VNAV shortly before the 8000ft constraint.

[matpietsch]

Next time look at the Oxy gauge and make sure you have enough oxygen for the flight

What to do if not? Can I fill it up?

[jarek]

So far so good.... (with checklist followed). Cabin keeps 9000 without problem.

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[jarek]

Dumping pressure - cabin climb indicates high rate, [cabin altitude] illuminated, cabin altitude pointer goes up. Right bleed air is off to decrease performance.

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Bleed valves open, outflow valve closed - cabin starts to pressurize again - cabin "descends". [cabin altitude] indication distinguishes at 10k.

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[matpietsch]

Hmm, strange. Thank you for checking it yourself.
The increase in cabin alt did not happen for me when trying to dump the cabin pressure. Which it should because from what I know about aircraft systems, dumping is pretty strait forward and as you don not simulate failures the cabin alt should raise when doing so no matter what, shouldn’t it?
Everything else I adjusted just like you did. I think that it is a hiccup somewhere in code. I did the same procedure as every flight (following the checklist).

What I found is that the plane often shows minor issues if you use slew mode (maybe to reposition it a bit on the ground) or use the GSX reposition feature. I do it rarely but all occurrences of minor, non repeatable bugs have that thing in common. So, there might be a correlation but not necessarily a causality.

[Heronjr]

I have been suffering this for some time and even posted about in this forum. I use to fly at FL210 or FL220 and the red light comes between 16000 to 17000 feet. My gauges are exactly positioned as yours, under the factory recommendations. This happens no matter the origin airport altitude is zero or 4500 feet.

Regards