OK folks...here it is from the mouth of a Northwest flight attendant.
Some of the DC9s have the ventral airstairs like the 727. While having similar exterior looks, they are not used in any manner like those on the 727. From the cabin there is either a plug hatch (that is lifted out and laid flat on the floor), or a pressure bulkhead (fancy name for a hinged door). THIS GETS COMPLICATED - READ CAREFULLY.
AIRCRAFT WITHOUT VENTRAL AIRSTAIRS
These aircraft have a 14ft catwalk that leads through the tail to the tailcone and slide, nothing complicated at all.
AIRCRAFT WITH VENTRAL STAIRS
The ventral airstairs are located below the 14ft catwalk that leads to the tailcone and slide. When you open the back pressure bulkhead or plug hatch, you'll see two things. Either a straight shot to the tailcone, or the catwalk up at an angle, exposing the airstairs beneath. Its like a reverse trap door that opens upwards. The stairs are opened from the outside, somebody ascends them halfway, pushed the 'reverse trap door' up at 45 degrees and goes in the back door of the cabin. These stairs CANNOT be opened from the inside (DUMB!). If your conducting an evacuation via the tailcone, and after opening the aft door you find the catwalk up, all you do it pull it down and continue as normal. All NWA evacuation procedures call for the tailcone and slide to be used. It would have made way more sense to refit these aircraft to use the airstairs instead.
The DC9 is NOT the first aircraft you encounter in initial flight attendant training at NWA. You are about 3/4 through aircraft training before doing the DC9. The tailcone is a very complicated (as far as emergency management) exit that many people have problems with at first. There are different commands for different styles of exit (pressure bulkhead vs. plug hatch) and many variations in the application of the use of the DC9s tailcone. The overwing exits are the primary means of egress in the back, with the tailcone to be used only if necessary. No flight attendant would ever hesitate at using the tailcone, but if the flight was light, would most likely force people forward to the overwing exits and 1L/R exits.
If you still have questions about the DC9 tailcone, post here or email me and ill answer. Ive got pics I took at NWA inside a real tailcone exit on the ground in GFK