The first ATA pilots were introduced to military aircraft at the RAF's Central Flying School (CFS), but the ATA soon developed its own training programme. Pilots progressed from light single-engined aircraft to more powerful and complicated aircraft in stages. They first qualified on one "class" of aircraft, then gained experience on that class by doing ferrying work with any and all aircraft in that class, before returning to training to qualify on the next class of aircraft. As a result, pilots made progress on the basis of their own capabilities rather than according to a rigid timetable. This ensured not only that as many pilots as possible advanced, but that those who could not were still gainfully employed flying the aircraft types on which they had qualified.