Walking the line Published Feb. 11, 2015 By 71st FTW Public Affairs 71st FTW Public Affairs VANCE AIR FORCE BASE, Okla. -- Every day hundreds of Undergraduate Pilot Training students take to the skies above northwest Oklahoma in a variety of training aircraft. Vance is one of the busiest air fields in North America. Students and instructors fly an average of 50,000 sorties a year.