the system of a fixed tail surface and moveable elevators is standard in subsonic aircraft. craft capable of supersonic flight often have a stabilator, an all-moving tail surface. pitch is changed in this case by moving the entire horizontal surface of the tail. this seemingly simple innovation was one of the key technologies that made supersonic flight possible. in early attempts, as pilots exceeded the critical mach number, a strange phenomenon made their control surfaces useless, and their aircraft uncontrollable. it was determined that as an aircraft approaches the speed of sound, the air approaching the aircraft is compressed and shock waves begin to form at all the leading edges and around the hinge lines of the elevator. these shock waves caused movements of the elevator to cause no pressure change on the stabilizer upstream of the elevator. the problem was solved by changing the stabilizer and hinged elevator to an all-moving stabilizer—the entire horizontal surface of the tail became a one-piece control surface. also, in supersonic flight the change in camber has less effect on lift and a stabilator produces less drag.