The DC-9 Classic manuals are now available as free downloads. If you would like to have a look at the User Manual (product details and features) or the Aircraft Operating Manual (operations and system descriptions) to see what the DC-9 Classic is all about or maybe get a head start on your type rating on the DC-9, please feel free to download them here.
Failure simulation. This is what in my opinion takes the DC-9 Classic, and all other addons that includes such a feature, to the next level. Usually when you simulate a system in an aircraft, you simulate ON or OFF in a normal state. With failure simulation a system can also be simulated ON or OFF in a failed state. While OFF is usually OFF regardless of state, ON and failed at the same time is where it can get really busy real fast on the flight deck.