.
center mark depicts neutral position

.
right mark depicts maximum right position.

Copyright . The Boeing Company. See title page for details.
9.10.18   June 1, 2005

737 Flight Crew Operations Manual

Introduction
The primary flight control system uses conventional control wheel, column and pedals linked mechanically to hydraulic power control units which command the primary flight control surfaces; ailerons, elevators and rudder. The flight controls are powered by redundant hydraulic sources; system A and system B. Either hydraulic 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 system B pressure is not available.
The secondary flight controls, high lift devices consisting of trailing edge (TE) flaps and leading edge (LE) flaps and slats (LE devices), are powered by hydraulic system B. In the event hydraulic system B fails, the TE flaps can be operated electrically. Under certain conditions the power transfer unit (PTU) automatically powers the LE devices. (Refer to Chapter 13, Hydraulics, Power Transfer Unit). They can also be extended using standby hydraulic pressure.
Pilot Controls
The pilot controls consist of:
.  
two control columns

.  
two control wheels

.  
two pairs of rudder pedals

.  
SPEED BRAKE lever

.
FLAP lever

.  
STAB TRIM cutout switches

.  
STAB TRIM override switch

.  
stabilizer trim switches

.  
stabilizer trim wheel

.  
AILERON trim switches

.  
RUDDER trim control

.  
YAW DAMPER switch

.  
ALTERNATE FLAPS master switch

.  
alternate flaps position switch

.  
FLT CONTROL switches

.  
flight SPOILER switches

The columns and wheels are connected through transfer mechanisms which allow
the pilots to bypass a jammed control or surface.

There is a rigid connection between both pairs of rudder pedals.
The SPEED BRAKE lever allows manual or automatic symmetric actuation of the
spoilers.

Copyright . The Boeing Company. See title page for details.
Flight Controls -System Description 737 Flight Crew Operations Manual

Flight Control Surfaces
Pitch control is provided by:
.
two elevators

.
a movable horizontal stabilizer. Roll control is provided by:

.
two ailerons

.
eight flight spoilers.

Yaw control is provided by a single rudder. During takeoff, the rudder becomes
aerodynamically effective between 40 and 60 knots.
TE flaps and LE flaps and slats provide high lift for takeoff, approach and landing.
In the air symmetric flight spoilers are used as speed brakes. On the ground

symmetric flight and ground spoilers destroy lift and increase braking efficiency.
Flight Control Surfaces Location

Copyright . The Boeing Company. See title page for details.
9.20.2  April 28, 2000

Flight Controls -System Description 737 Flight Crew Operations Manual
Roll Control
The roll control surfaces consist of hydraulically powered ailerons and flight spoilers, which are controlled by rotating either control wheel.
Ailerons
The ailerons provide roll control around the airplane’s longitudinal axis. The ailerons are positioned by the pilots' control wheels. The A and B FLT CONTROL switches control hydraulic shutoff valves. These valves can be used to isolate each aileron, as well as the elevators and rudder, from related hydraulic system pressure.
The Captain’s control wheel is connected by cables to the aileron power control units (PCUs) through the aileron feel and centering unit. The First Officer’s control wheel is connected by cables to the spoiler PCUs through the spoiler mixer. The two control wheels are connected by a cable drive system which allows actuation of both ailerons and spoilers by either control wheel. With total hydraulic power failure the ailerons can be mechanically positioned by rotating the pilots' control wheels. Control forces are higher due to friction and aerodynamic loads.
Aileron Transfer Mechanism
If the ailerons or spoilers are jammed, force applied to the Captain’s and the First Officer’s control wheels will identify which system, ailerons or spoilers, is usable and which control wheel, Captain’s or First Officer’s, can provide roll control. If the aileron control system is jammed, force applied to the First Officer’s control wheel provides roll control from the spoilers. The ailerons and the Captain’s control wheel are inoperative. If the spoiler system is jammed, force applied to the Captain’s control wheel provides roll control from the ailerons. The spoilers and the First Officer’s control wheel are inoperative.
　
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