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NG cabin ROC fluctuating

PostPosted: 29 Aug 2018, 23:14
by Shumway
There's been quite a few reports during cruise cabin ROC fluctuates, about 500ft/min. Duct pressure is stable.
Ground pressurisation check found satisfactory within leak rate limits. CPC bite shows low in flow / hi leakage.

Any idea what could cause this?

Re: NG cabin ROC fluctuating

PostPosted: 01 Sep 2018, 15:59
by Dunny
vacuum toilet use can cause a brief change in rate of climb

Re: NG cabin ROC fluctuating

PostPosted: 02 Sep 2018, 02:46
by Shumway
Definitely not toilet usage, it happens throughout, even without toilet being used...

Re: NG cabin ROC fluctuating

PostPosted: 02 Sep 2018, 16:49
by Dunny
I would have thought +/- 500ft cabin alt ROC would have been able to be felt in the ear.

Are the pilots reporting an actaul cabin alt change or just the needle on the gauge fluctuating ?

Re: NG cabin ROC fluctuating

PostPosted: 04 Sep 2018, 14:41
by Shumway
This defect has occurred on several aircraft, definitely not indication, most pilots don't really complain if it's 500fpm , but there was one which went up to almost 1000fpm & everyone (that means pax too) complained of ear discomfort.
Can't be CPC either cause changed to alternate as still the same.

Re: NG cabin ROC fluctuating

PostPosted: 05 Sep 2018, 12:35
by motortek
just check temperature control valves.

Re: NG cabin ROC fluctuating

PostPosted: 06 Sep 2018, 16:07
by Dunny
How about the pack flow control shut off valve or the Trim air PRSOV, but of these have a pressure regulating function.

Re: NG cabin ROC fluctuating

PostPosted: 19 Sep 2018, 04:58
by yayoo
suggest to check the cargo door seal per FIM 21-31 Task 823 step B (6).

Re: NG cabin ROC fluctuating

PostPosted: 26 Jan 2019, 22:23
by Stenovic
As per FIM last manufactured Airplanes got this problem due to TCV. They still modulating and causing ROC fluctulation.