Hi,I have a few questions regarding the PMDG's (600-900) systems.1) Could someone clarify the operation of the isolation valve? I've been told it should be closed before cockpit acceptance, then positioned to auto after the packs have been switched on. Also, should it be open after shutdown?2) Also on the subject of a/c, how many packs should be in operation before start? I've heard that only one is necessary.3) In PMDG's checklists, the APU fire handle should be up during the exterior pre-flight inspection. Doesn't this kill the APU? What's the reason for this?4) It also says to position the outflow valve to open during this stage of the flight. For this, should control of the outflow be switched to man? If so, when should it be closed again or reset to auto?Thanks.

...Anyone?... :)

I'm sure someone here will be able to answer your questions; they are a very knowledgeable bunch!!In the meantime take a look at http://www.b737.org.uk/ which might answer some of your questions.Hope it helps,

JamesFirst of all I'll do my usual bit and say I am NOT an NG driver but I do drive the 3/4/500 series for a living and most things are the same:Answers to your questions:1) The isolation valve on the classic remains in AUTO all the time unless circumstances require it to be operated in the manual positions (ie an emergency checklist for instance). The isol valve has a logic to it which keeps us out of trouble in most cases. When in AUTO it - will OPEN if any CORNER (ie packs or bleeds) switch is in the OFF positionWill CLOSE if all corner switches are in the ON positionWe leave the isol valve switch in AUTO 99.9% of the time and there is no reason for you to CLOSE it or OPEN it manually in normal operations on the ground or in the air!2) Boeing say that only one pack should be used per bleed air source so when on the ground you only have one bleed source (the APU) and so should only use the one pack. just prior to start the pack should be turned off in order to get a sufficient pressure in the duct to start the engines! The way that the a/c system is designed yes only one pack is necessary you however get to choose which one. If you are mean and don't care about your paying public then the LEFT is the choice as this supplies most of its output direct to the flight deck. The right provides air only to the MIX MANIFOLD and thus supplies to the entire cabin /flight deck evenly and thus ensures happy passengers and happier cabin crew thus decresing the likelyhood of spit in your coffee3)I have only ever pulled a fire handle on the sim and hope it shall remain so for some time. There is no reason to pull the fire handle unless something is on fire (hence the name) this may be an NG procedure but not something I've ever heard of. Yes it would kill the APU. There is a fire check which should be done prior to starting the APU but we frequently arrive at the aircraft with the APU already running and thus the fire check having been completed by the engineers! 4) There shoule be no reason to move the outflow valve assuming the system is working correctly in AUTO and the FLT/GND switch set to GND but I understand that the NG doesn't have a FLT/GND switch so there should be no problem there. The system automatically motors the outflow valve to fully open once the aircraft has landed. This ensures the aircraft has fully depressurised and thus prevents one fo the cabin crew being blown out of the door onto the airbridge when they open the door. This again will cause the spit content in your coffee to increase! Seriously though the NG may require this but we don't on the classic. If nothing else you can see the position of the outflow valve on the panel anyway and if that is bust you can visually check it on the walk around.Hope that helps Kris