Throughout a normal flight, a pilot controls an aircraft through the use of flight controls including maintaining straight and level flight, as well as turns, climbing, and descending. Some controls, such as a "yoke" or "stick" move and adjust the control surfaces which affects the aircraft's attitude in the three axes of pitch, roll, and yaw. Other controls include those for adjusting wing characteristics (flaps, slats, spoilers) and those that control the power or thrust of the propulsion systems. The loss of primary control systems in any phase of flight is an emergency. Aircraft are not designed to be flown under such circumstances; however, some pilots faced with such an emergency have had limited success flying and landing aircraft with disabled controls.
Control system failures resulting in disabled controls have resulted in a number of aviation incidents and accidents. Some incidents occurred where controls were not functioning correctly prior to take-off, others where the failure developed during flight. A loss of control can occur when an unrelated failure, such as an engine failure, causes damage to control related systems. For instances, in several incidents an engine broke apart, causing the failure of main and redundant hydraulic systems, which disabled all control surfaces. Some or all controls can become inoperative from extreme weather conditions, due to collisions, due to poor maintenance or mistakes made by maintenance workers, as a result of pilot error, due to failures of the flight control system, or due to design or manufacturing flaws.