CJ2+ Cabin Altitude warning

[JliderPilot]

Looking for a bit of advice.

Been flying the CJ2+ for 7 months now (the aircraft has only 700 hrs on it and is just over 2 yrs old), we have had two separate incidents of cabin alt warnings. on both occasions we were above FL410; and both times it was spurious i.e. diff pressure was normal and cabin altitude was normal. the warning went away in the descent passing about FL220. The first time the engineers changed the PCB that has the pressure switch on it, now the fault has returned about 3 months later.

I've heard this has happened before on the CJ, anyone had experience of this?

[First.officer]

Hi JliderPilot,

Recall getting warnings of "Door Seal" in the older CJ2 models sometimes, and currently fly the CJ2+ myself, but not come across this one....might be worth sending off a quick email to [email protected] - they might have some good ideas/areas to explore....

F/o

[G-DAVE]

Had this a few times. The problem seems to arise from water in the pressurisation system freezing in the door seal area, causing a spurious warning to appear.

A way to prevent this happening is with the No.2 engine running, and the door open, pressing the valve in (theres a small valve in one of the holes on the left hand side of the door opening on the fuselage) and you will see and hear water vapour and air dispersing through the bleed air valve. When you can no longer feel any water escaping, you're done. Repeat frequently, especially when its been raining.

[JonDyer]

He definitely said:

...we have had two separate incidents of cabin alt warnings. My bold.

You two are taking about door seal issues.

[First.officer]

No, no, no Jon my dear boy......I merely mentioned the only problem I ever saw on the CJ2 (and not the CJ2+), and hence I suggested a quick email might help, hence my comment "not come across this one".......thus, for clarity....I've personally not seen a Cabin Alt warning myself. :E;)

[His dudeness]

I once flew a relatively old CJ with that problem. (which the operator did´nt bother to tell me at all, the freelance copilot did casually when the went through FL 150 and the light came one and disappeared a very short time later (cabin alt and diffpress were holding) .

Can´t tell you what the issue was, cause I decided not to fly for this dude again.

But that was the only time I had that in about 2000hrs in all variants of the C525 but the CJ4.

[JonDyer]

Can´t tell you what the issue was, cause I decided not to fly for this dude again.

You say that like you expect them to have fixed it. I don't suppose they can tell you what the issue is either!

[His dudeness]

No idea JD, but I made my decision partly (small part though) because I thought that I like an operator to tell me things like that before I fly his airplane. Apparently the issue was known for quite some time. (I would not consider this to be a major problem, as one has diffP and cab alt to crosscheck)

Whether they decided not to look after it or maintenance did not find the reason I don´t know.

[G-DAVE]

He definitely said:

Quote:
Originally Posted by JliderPilot
...we have had two separate incidents of cabin alt warnings.
My bold.

You two are taking about door seal issues.

I hear you. But this issue did cause the CAB ALT to annunciate during flight. By bleeding the system of water that can freeze, has stopped the problem.

[JliderPilot]

Thanks for your responses guys, I was aware of the door seal trick but thought that was just if you got the door seal annunciation. I'll do some more digging.

[tommoutrie]

Although the cabin altitude master caution will trigger in the event of the cabin rising above 13k or whatever it is, it will also trigger if it receives invalid information. It's unlikely to be the logic board but I think cabin pressure in a CJ is sensed by a number of pressure transducers and its likely to be a miscompare in the outputs from these transducers that's triggering the warning. This is especially true if its repeatable and happens at consistent differentials and cabin pressures. I would note what they are and specifically ask an engineer to check the transducer calibrations.


Or some similar bull****..

[JliderPilot]

Will do, cheers