Several aviation incidents and accidents have occurred in which the control surfaces of an aircraft became disabled, often due to failure of hydraulic systems or the flight control system. Other incidents have occurred where controls were not functioning correctly prior to take-off, either due to maintenance or pilot error, and controls can become inoperative from extreme weather conditions. Aircraft are not designed to be flown in such circumstances; however, a small number of pilots have had some success in flying and landing aircraft with disabled controls.