johnnybroom

Ok, that makes sense. The whole temperature arc is technically AUTO so moving the selector to 9 o'clock, for instance, is just saying "cooler," not "cooler than auto." It *still* bothers me, though, that the 12 o'clock position, presumably half-way between the warmest and coldest, offers such varying temperatures, and the main concern here, occasionally such hostile temperatures. As Spin noted (in agreement with FCOM) the selector range is 18ºC to 30ºC, so how could I be getting 40ºC air in the supply ducts with the selector in the middle (default)? Isn't that just indication that the automation of trim air is going nuts, trimming the already-comfortable PACK air a good 20ºC more, out of the normal temp range? Are there really conditions (even cold weather ops, e.g.) in which you'd need that much hot bleed air trimming the ~20ºC PACK air to provide a warm cabin? Bryan Yunis

Thanks, VLJ. I'll try that. Are you aware of any repercussions of turning trim air off, other than the inability to modulate specific zones? I suppose that's kind of the "default" setting, like Cristi said, so I'd just be getting relatively comfortable PACK air. Do you turn the trim air back on at any point in the flight? Also, thanks for the tip re: my name. I changed the original post. Bryan Yunis

Sorry if this has been already posted (I did my best to search the forum). I have been encountering the following problem: a quick rise to 40+ C. air in certain supply ducts (usually AFT and/or CONT CAB) shortly after I either switch on the APU bleed or start the engines thus using engine bleeds for bleed air. In turn, my cabin temp rises substantially -- if I don't notice it right away, sometimes cabin temps get into the mid 40s C. and I get an amber zone temp alert. All temperature control switches are set to AUTO, the problem happens regardless of outside air temperature, and my RAM doors are fully open during this problem. PACK temperatures are normal, with right pack temp registering around 19 C., and the left slightly higher at around 23 C. If I move the appropriate temperature control switch(es) to a cooler setting (one or two notches into the "cold" range), the respective supply duct temperature quickly decreases to an acceptable range. My question is twofold: 1. The problem doesn't seem to be with the PACKs, since their temps are normal, and my problem involves temps jumping extremely only in certain zones (indicating mix manifold temp is normal). With mix manifold temp normal, the air must be getting heated somewhere between the manifold and the supply duct -- the only thing I can imagine is the trim air going nuts and thinking it needs to modulate (i.e. heat) the individual supply duct zones way (way) more than it does. I could shut off the trim air system entirely, or the individual trim air modulating valves by selecting OFF on the respective temperature control switch, but that would seem an unnecessary (and perhaps dangerous) step to having a comfortable cabin when AUTO should keep temps normal. Furthermore, when the amber zone temp light illuminates as it does when I fail to notice the temp rise, the associated trim air modulating valve should close (perhaps it does not in the NGX simulation), yet even so, the supply duct temp does not cool until I move the temp selector into the "cold" range. Does anyone know if trim air does this sometimes, and what I can do to remedy it? Do I have the wrong idea assuming this is a trim air malfunction? 2. Am I doing something procedurally wrong that could somehow be subjecting my virtual passengers to an oppressive, tropical climate? My pneumatic system initiation procedure with APU bleed is standard, as I understand it, with APU ignition, trim air defaulted on, recirculation fans switched to auto, PACKs switched to auto, isolation valve switched to open, and all bleeds turned on. If this is just a real-life NG idiosyncrasy, I'll continue to deal with it manually as I mentioned, but it seems hardly likely most pilots would be alright with such a quirk, 40-degree C air blowing on their passengers with temp controls set to AUTO. Or, perhaps, is this a fix that PMDG needs to institute? Thanks guys, Bryan Yunis