Essentially, you need to be posted to an Air Force base that has hard flight medical positions - Trenton, Winnipeg, Bagotville, Comox, Cold Lake, North Bay and such. In fact, at the time I did my medevac course, , if you were not fit to fly (as crew), you weren't supposed to be posted to one of those Wings Trenton is just one place, but crews can come from anywhere to meet a need - Trenton just happens to have alot of the aircraft used.
MM