Change 3 2-43
or aft, until the locking pin engages in the selected posi-
b. Yaw Damper System. A yaw damper system is
provided to aid the pilot in maintaining directional stability
and increase ride comfort. The system may be used at
any altitude, but is required for flight above 17,000 feet.
It must be deactivated for takeoff and landing. The yaw
damper system is a part of the autopilot. Operating in-
structions for this system are contained in Chapter 3. The
system is controlled by a YAW DAMP switch located on
the autopilot control panel.
c. Rudder Boost System. The rudder boost system is
a torque sensing, linear actuating system. The system
utilizes a pressure transducer on each engine to sense
engine torque oil pressure, a stability augmentation com-
puter to monitor torque levels, and the rudder servo to
apply boost to aid the pilot.
The stability augmentation computer monitors torque
levels and airspeed to determine if boost is required. The
level of boost is proportional to the difference in torque
between each engine and inversely proportional to air-
speed. Boost commences at approximately 50% torque
differential and increases to maximum at 100% torque
differential. The level of boost available is inversely pro-
portional to airspeed such that maximum rudder boost is
obtained at 100% differential and low airspeed (80
knots), while no rudder boost is available at high air-
speeds (above 180 knots).
The rudder boost system is controlled by a switch
placarded RUDDER BOOST - OFF - YAW CONTROL
TEST, located on the pedestal extension (fig. 2-12). The
rudder boost system is powered through a 5-ampere
circuit breaker placarded RUDDER BOOST, located on
the overhead circuit breaker panel (fig. 2-7).
2-38. FLIGHT CONTROL LOCKS.
Remove control locks before towing the aircraft
or starting engines. Serious damage could result
in the steering linkage if towed by a tug with the
rudder lock installed.
Positive locking of the rudder, elevator and aileron
control surfaces, and engine controls (POWER levers,
PROP levers, and CONDITION levers) is provided by a
removable lock assembly (fig. 2-23) consisting of two
pins, and an elongated U-shaped strap interconnected
by a chain. Installation of the control locks is accom-
plished by inserting the U-shaped strap around the
aligned control levers from the copilots side; then the ai-
leron/elevator locking pin is inserted through a guide hole
in the top of the pilots control column assembly. The rud-
der is held in a neutral position by an L-shaped pin which
is installed through a guide hole in the floor aft of the pilots
rudder pedals. The rudder pedals must be centered to
align the hole in the rudder bellcrank with the guide hole
in the floor. Remove the locks in reverse order (rudder
pin, control column pin, and power control clamp).
2-39. TRIM TABS.
Trim tabs are provided for all flight control surfaces.
These tabs are manually actuated, and mechanically
controlled by a cable-drum and jack-screw actuator sys-
tem except the right aileron tab which is of the fixed,
bendable type. Elevator and aileron trim tabs incorporate
neutral, non-servo action, i.e., as the elevators or aile-
rons are displaced from the neutral position, the trim tab
maintains an as-adjusted position. The rudder trim tab in-
corporates anti-servo action, i.e., as the rudder is dis-
placed from the neutral position the trim tab moves in the
same direction as the control surface. This action in-
creases control pressure as rudder is deflected from the
a. Elevator Trim Tab Control. The elevator trim tab
control wheel placarded PITCH TRIM, DN - UP, is located
on the left side of the control pedestal and controls a trim
tab on each elevator (fig. 2-12). The amount of elevator
tab deflection, in units from a neutral setting, is indicated
by a position arrow.
b. Electric Elevator Trim. The electric elevator trim
system is controlled by an ELEV TRIM - OFF/RESET
switch located on the pedestal extension (fig. 2-12), dual
element thumb switches on the control wheels (fig. 2-22),
a trim disconnect switch on each control wheel, and a
5-ampere circuit breaker placarded ELEC TRIM, located
on the overhead circuit breaker panel (fig. 2-7). The ELEV
TRIM - OFF/RESET switch must be in the ELEV TRIM
(on) position to operate the system. The dual element
thumb switch is moved forward for trimming nose down,
aft for nose up, and when released returns to the center
(off) position. Any activation of the trim system through
the copilots trim switch can be over-ridden by activation
of the pilots switch. Operating the pilots and copilots
switches in opposing directions simultaneously results in
the pilot having priority. An annunciator placarded ELEC
TRIM OFF on the caution/advisory annunciator panel in-
dicates failure or disconnect of the electric trim system.
A preflight check of the switches should be
accomplished before flight by moving the switches indi-
vidually on both control wheels. No one switch alone
should operate the system; operation of elevator trim
should occur only by movement of pairs of switches. The
trim system disconnect is a bi-level pushbutton momen-
tary-type switch, located on the outboard grip of each