Why do you have to open the pneumatic crossfeed valves to de-ice the wings? Exactly what does the AC bus cross-tie switch do? And why do the engines only draw fuel from the center tank when all the fuel booster pumps are on? The key to understanding these and many other aspects of your aircraft is studying the schematic drawings for the various aircraft systems. That may sound a little bit dry, but to help you out I have included a Schematics section in the DC-9 Classic Flight Center that gives you live interactive schematic drawings.
What exactly is specularity and how does it work in FSX? On the Coolsky support forum McPhat Studios explains in detail how specularity works on the new upcoming soon-to-be-released freeware American Airlines UHDT livery.
Just recently came across an article on the Internet that detailed the differences between the various DC-9 models, as well as the MD-80 series, the MD-90 and B717. I thought it was a very interesting article and I wanted to share it with you.