Complex sentence: Concurrently, the Air Force also commenced a phaseout of its long-standing Aviation Cadet (AvCad) program at Lackland AFB, the graduates of which had to successfully complete either undergraduate pilot training or undergraduate navigator training before they could be commissioned as 2d Lieutenants.
Split into simpler sentences: Concurrently, the Air Force also commenced a phaseout of its long-standing Aviation Cadet (AvCad) Program at Lackland AFB. In addition, AvCads had to successfully complete either undergraduate pilot training or undergraduate navigator training before they could be commissioned as 2d Lieutenants.