Hydraulics

Four independent systems (designated A, B, L, and R) supplied hydraulic power to the A‑12, thereby facilitating operation of the control actuators, landing gear, and other equipment. The A and B systems operated in parallel, supplying hydraulic pressure to the flight controls, specifically the seven actuating cylinders on each outboard elevon, the three on each inboard elevon, and the two cylinders operating each rudder. A dual servo unit, one for each movable flight control surface, controlled system pressure and return of fluid to the actuating cylinders.

The L and R systems supplied hydraulic power to the left and right inlet spikes and the forward and aft bypass doors on each nacelle. The L system also served the normal brake system, landing gear, main gear inboard doors, nose wheel steering system, refueling door and fuel probe receptacle latches. The R system supplied hydraulic power to the alternate braking system, alternate nose wheel steering system, landing gear retraction system, and backup system for closing the main landing gear inboard doors. Each system was serviced by its own hydraulic reservoir and fixed‑angle, variable‑volume piston pump. The left engine drove the A and L system pumps, while the B and R pumps were driven by the right engine.