Originally Posted by
hans brinker
CJ3 does not have an ACM....
We may be nitpicking here, but the CJ3 belongs to the the line of "CitationJets" which are all part 23 certified aircraft, whereas the line of "Citations", to which the accident C560 belongs, are part 25 certified and all of them have, among other differences, an air cycle machine. In my 3.500+ hours on Citations I have had two pressurisation issues so far. One was due to pilot error (because of "finger trouble" the pressurisation switch was selected to "Manual" when really the switch next to it should have been flipped - these things happen when switches are moved without looking) and the other was caused by a faulty outflow valve.
Because it has been mentioned above: 1) The cabin air at altitude is very dry because it always passes through a water separator. 2) A door seal fault is indicated by an amber warning light together with a master caution. There is a secondary (passive) door seal and even a failure of the inflated door seal should not result in a rapid decompression. 3) Some malfunctions of the air cycle machine will automatically switch the system to "emergency pressurisation" mode, which means that the cabin will continue to be pressurised with pure bleed air. Hot and uncomfortably loud (they say) but breathable. 4) The optional freon air conditioner is totally unrelated to the pressurisation system. It is electrically operated and can be used from the ground up to 18.000ft.