• 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 power
    control units ( 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.
The roll control surfaces consist of
hydraulically powered ailerons and
flight spoilers which are controlled
by rotating either control wheel.
B737-700/800/900  Flight Controls - Roll Control
Flight Controls SGR