BOEING 737 FLIGHT CONTROL SYSTEMS. The primary flight controls, ailerons, elevators and rudders, are hydraulically powered. Hydraulic power is provided from hydraulic systems A and B; either system can operate all primary flight
controls. ¡ The ailerons and elevators may be operated manually if required. The rudder may be operated by the standby hydraulic system if system A and/or B pressure is not available. ¡ The ailerons are assisted by flight spoilers for roll control. The spoilers are hydraulically powered from system A (inboard) and B (outboard) and operate proportionally with aileron movement. The horizontal stabilizer may be positioned by electric trim, or manually through the trim wheels. During automatic flight, the autopilot trim controls the stabilizer position. ¡ The Surface Position Indicator (if installed), located on the Captain’s instrument panel, or, on 737NG the system display on the lower Display Unit, displays deflection of the ailerons, rudder and elevators. Aerodynamic braking is provided in flight by the flight spoilers operating as speedbrakes. On ground, flight spoilers and ground spoilers are used in combination to destroy lift. ¡ High lift for take-off and landing is provided by trailing edge flaps and leading edge flaps and slats (LE devices). Normally, these surfaces are extended and retracted by hydraulic system B. Alternatively, the trailing edge flaps may be extended and retracted electrically. The leading edge devices may be extended by the standby hydraulic system. No alternate retraction system is provided for the leading
edge devices. ¡ The autoslat system improves handling qualities at high angles of attack during operations with flaps
set at positions 1 through 5. Autoslat operation deploys the slats from intermediate to full extended
position prior to stick shaker activation.

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