Pressure altitude showing 44000 ft when flying at 28000 ft
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I'm getting a crazy high pressure altitude, resulting in a CABIN DIFF HIGH warning light:
Why would it show this pressure? My barometer is set to 29.92. No active failures.
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The small needle and inner scale of the instrument isn't displaying altitude, it's displaying the cabin differential pressure. Read the small inner scale with the red line. The outer scale shows cabin altitude, the inner scale shows cabin differential. You're getting the CABIN DIFF HIGH warning because the cabin differential in this case has well exceeded its limit of 8.5psi.
The altimeter setting has no effect or relationship to the pressurization system.
You probably haven't set the cabin controller correctly. Make sure it's set for your cruising altitude, and the system should schedule the cabin normally.
I'd be curious to ask Nick why the safety valve hasn't opened in this case, though.
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The cabin controller was set to 30000 and I was flying at 28000...
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Show us the pressure controller panel. Did you move the little knob away from Auto? Is the rate knob set to very low? It looks like its depressurizing, but very slowly.
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Show us the pressure controller panel. Did you move the little knob away from Auto? Is the rate knob set to very low? It looks like its depressurizing, but very slowly.
@jmarkows said in Pressure altitude showing 44000 ft when flying at 28000 ft:
Show us the pressure controller panel. Did you move the little knob away from Auto? Is the rate knob set to very low? It looks like it’s I depressurizing, but very slowly.
Unfortunately I didn’t take a screenshot of the knobs. I left the little knob at 10 o clock, then twisted it clockwise a bit after getting the warning. But if it was just pressurizing slowly, shouldn’t it have reached the target pressure eventually? The warning was always on for like an hour. My question is why is the outside gauge showing 40000+, normally this shows roughly my actual altitude.
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@jmarkows said in Pressure altitude showing 44000 ft when flying at 28000 ft:
Show us the pressure controller panel. Did you move the little knob away from Auto? Is the rate knob set to very low? It looks like it’s I depressurizing, but very slowly.
Unfortunately I didn’t take a screenshot of the knobs. I left the little knob at 10 o clock, then twisted it clockwise a bit after getting the warning. But if it was just pressurizing slowly, shouldn’t it have reached the target pressure eventually? The warning was always on for like an hour. My question is why is the outside gauge showing 40000+, normally this shows roughly my actual altitude.
@Marionettework said in Pressure altitude showing 44000 ft when flying at 28000 ft:
Unfortunately I didn’t take a screenshot of the knobs. I left the little knob at 10 o clock, then twisted it clockwise a bit after getting the warning. But if it was just pressurizing slowly, shouldn’t it have reached the target pressure eventually? The warning was always on for like an hour. My question is why is the outside gauge showing 40000+, normally this shows roughly my actual altitude.
It's not, as mentioned the little hand is pointing to the inner ring, which is the cabin pressure differential. The big hand is pointing to cabin altitude, which in your case is about 2000ft and decreasing. You're not letting air out of the cabin for one reason or another.
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@Marionettework said in Pressure altitude showing 44000 ft when flying at 28000 ft:
Unfortunately I didn’t take a screenshot of the knobs. I left the little knob at 10 o clock, then twisted it clockwise a bit after getting the warning. But if it was just pressurizing slowly, shouldn’t it have reached the target pressure eventually? The warning was always on for like an hour. My question is why is the outside gauge showing 40000+, normally this shows roughly my actual altitude.
It's not, as mentioned the little hand is pointing to the inner ring, which is the cabin pressure differential. The big hand is pointing to cabin altitude, which in your case is about 2000ft and decreasing. You're not letting air out of the cabin for one reason or another.
@jmarkows said in Pressure altitude showing 44000 ft when flying at 28000 ft:
@Marionettework said in Pressure altitude showing 44000 ft when flying at 28000 ft:
Unfortunately I didn’t take a screenshot of the knobs. I left the little knob at 10 o clock, then twisted it clockwise a bit after getting the warning. But if it was just pressurizing slowly, shouldn’t it have reached the target pressure eventually? The warning was always on for like an hour. My question is why is the outside gauge showing 40000+, normally this shows roughly my actual altitude.
It's not, as mentioned the little hand is pointing to the inner ring, which is the cabin pressure differential. The big hand is pointing to cabin altitude, which in your case is about 2000ft and decreasing. You're not letting air out of the cabin for one reason or another.
Ok. I clearly did not understand how to read this guage
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I would be more interested to know if you have a stuck safety valve, since the cabin is still pressurizing beyond the differential limit. This would appear in your list of failures, and as a red valve on the cabin visualizer. There is some hysteresis in the valve, so it's possible that you caught it between actuations somewhere between 8.5-9.0 PSI.
