and feathered as described above. Also, pressing
Q6. What propeller system is used only during
in the feather switch causes the feather cycle
takeoff?
operation to take place.
When the flight crew restarts an engine
during flight, pull the feather switch out to the
Q7. During ground propeller unfeathering, how
UNFEATHER position and hold it there. The
feather cutout relay is de-energized, and power
do you decrease blade angle below 45
degrees?
goes to the feather pump power relay. The feather
pump motor pressure builds up and oil flows to
the decrease pitch side of the propeller dome,
causing the propeller to start unfeathering. During
APPROACH POWER
restarts the feather valve solenoid energizes during
COMPENSATOR SYSTEM
NTS inoperative conditions only.
When blade angle decreases to less than 45
Learning Objective: Recognize operating
degrees, the beta cam air start switch closes,
p a r a m e t e r s and features of aircraft
completing the path for current through the air
start control relay. The air start control relay
approach power compensator systems.
energizes the feather valve solenoid. This causes
The approach power compensator (APC)
the propeller blades to increase toward the feather
system (fig. 5-25) automatically controls engine
position. The beta cam air start switch opens at
power to maintain the best angle of attack during
48-degree blade angle, causing the air start control
landing approaches. This permits the pilot to
relay and feather solenoid valve to de-energize.
This causes cycling of blade angle around the air
direct most of his attention toward flying the
approach. During an APC approach in light to
start beta cam switch (45 degrees) and causes the
moderate turbulence, the set can maintain
NTS INOP warning light to flash. The light blinks
airspeed within a range of 4 knots.
because of the blade angle cycling action. At this
The major components of the system are a
indication, the flight crew pulls the emergency
control panel, accelerometer, computer, control
shutdown handle to abort the restart.
amplifier, a potentiometer to detect changes in
elevator position, and a rotary actuator, which
moves the throttle linkage. The aircraft angle-of-
REVIEW SUBSET NUMBER 10
attack transducer supplies angle-of-attack signals
to the computer. A compression switch on the
Q1. The propeller is used to convert engine shaft
landing gear breaks the APC circuit upon
horsepower to
touchdown.
With the landing gear down and weight off
the gear, the APC is energized by placing the
engage switch to ON. The switch is magnetically
Q2. W h a t mechanical unit maintains a
held on until the aircraft touches down, the
minimum blade angle?
throttle overrides the system, or the pilot places
the engage switch to OFF. The APC will also
release automatically if either the override switch
or the compression switch fails.
Q3. What does the beta follow-up system
With the set engaged, the accelerometer,
provide?
angle-of-attack transducer, and the ambient
temperature selector switch supply information
to the computer. The APC computer also receives
elevator position signals from a potentiometer
Q4. What system resets pitchlock RPM from
mounted in the control valve linkage of the
103.5 percent to 109 percent during an
elevator actuator. When normal acceleration is
aborted takeoff?
1 g and the angle of attack is optimum for a
landing approach, the computer sends no cor-
rective signal and the throttle position does not
Q5. What valve bypasses all other control
change. The computer interprets deviations from
these values as either offsetting each other or as
functions to feather the propeller?
