What determining factors make a "special duty" assignment a special duty?

I think they consider any long term assignment that is outside the scope of your normal AFSC duties. Like MTI, recruiter etc. For the officers/pilots we have Staff tours, or flying at undergraduate pilot training or flying the white jets. Once upon a time RPA's were considered a special flying duty. That changed in the two years I was doing it and became a primary AFSC.

I see you are at El forko Grande'. I was stationed there when it was the 319th Air Refueling Wing . Whats it like being there now? Is the base finally getting a mission, since takers departed the fix? I have been curious what the base even does now other than support Cavalier Air Station.

This article states: Military training instructors fill special duty positions, along with recruiters, honor guradsmen and several other career fields. For more information about developmental special duties, refer to PSDM 13-62 and the revised SPECAT

http://www.acc.af.mil/news/story.asp?id=123370989