Redundant or emergency steering mechanism especially for an aircraft

A redundant emergency control mechanism for steering an aircraft, comprising pilot controlled mechanical steering means (1, 2), first pressure transducer means (3) operatively connected to said pilot controlled mechanical steering means (3) for converting a movement of said mechanical steering means into a first hydraulic steering control signal component representing a pilot control action, operating condition sensor means (12) which are independent of an electrical power supply for sensing instantaneous flight operating conditions, second pressure transducer means (13) operatively connected to said operating condition sensor means (12) for converting flight operating condition representing signals into flight operating condition representing second hydraulic steering control signal components, pressure operated control actuator means (18) including a source of pressure (P) and conduit means operatively connecting said control actuator means (18) to said first and second pressure transducer means for receiving said first and second hydraulic steering control signal components in a superimposed manner in said control actuator means (18) for converting the resulting combined signal into a mechanical steering control action when an electrical power supply failure occurs in the aircraft, said mechanism further comprising pressure operated power actuator means (25), valve means (23) operatively connecting said second pressure transducer means (13) to said pressure operated power actuator means (25), and mechanical linkage means (22, 24, 26) operatively interconnecting the output (22) of said pressure operated control actuator means (18) to the respective outputs (26, 24) of said valve means (23) and of said pressure operated power actuator means (25), whereby an operation of said control actuator means (18) overrides the normal automatic operation of said power actuator means (25).