To prevent an asymmetrical thrust condi-
tion, propeller levers must be in HIGH
RPM position prior to propeller revers-
The propeller blade angle may be reversed to
shorten landing roll. To reverse, propeller levers
must be positioned at HIGH RPM (full forward),
and the power levers are lifted up to pass over the
IDLE detent, then pulled aft into REVERSE setting.
One yellow caution light, placarded REV NOT
READY, on the caution/advisory annunciator panel,
alerts the pilot not to reverse the propellers. This
light illuminates only when the landing gear handle
is down, and if propeller levers are not at HIGH
RPM (full forward). This circuit is protected by a
5-ampere circuit breaker, placarded LANDING
GEAR RELAY, located on the overhead circuit
breaker panel (fig. 2-26).
2-49. PROPELLER TACHOMETERS.
Two tachometers on the instrument panel regis-
ter propeller speed in hundreds of RPM (fig. 2-29).
Each indicator is slaved to a tachometer generator
unit attached to the corresponding engine.
2-50. DEFROSTING SYSTEM.
Description. The defrosting system is an
integral part of the heating and ventilation system.
The system consists of two warm air outlets con-
nected by ducts to the heating system. One outlet is
just below the pilots windshield and the other is
below the copilots windshield. A push-pull control,
placarded DEFROST AIR, on the pilots subpanel,
manually controls airflow to the windshield. When
pulled out, defrosting air is ducted to the wind-
shield. As the control is pushed in, there is a corre-
sponding decrease in airflow.
b. Automatic Operation.
Vent blower switches - As required.
2. Cabin temperature mode selector
switch - AUTO.
3. Cabin temperature control rheostat -
4. Cabin air, copilot air, pilot air, and
defrost air controls - As required.
Pilot air, copilot air - IN.
Cabin air and defrost air controls - Out
3. Cabin temperature mode selector
switch - MAN HEAT.
Cold air outlets - As required.
5. Manual temperature switch - As
d. Manual Operation. If the automatic tem-
perature control should fail to operate, the tempera-
ture (of defrost air and cabin air) may be controlled
manually by setting the CABIN TEMP MODE con-
trol switch to MANUAL COOL position, then using
the MANUAL TEMP DECREASE-INCREASE
switch to set the desired temperature. This control is
located on the overhead control panel (fig. 2-l 2).
SURFACE DEICING SYSTEM.
a. Description. Ice accumulation is removed
from each inboard and outboard wing leading edge,
both horizontal stabilizers, the taillets, and certain
mission antennas by the flexing of deicer boots
which are pneumatically actuated. Bleed air from
the engine compressor is used to inflate the deicer
boots and to supply vacuum, through the ejector sys-
tem, for boot hold down during flight. A pressure
regulator protects the system from over inflation.
When the system is not in operation, a distributor
valve applies vacuum to the boots for hold down. A
selector switch allows automatic single cycle opera-
tion or manual operation. To assure operation of the
system in the event of failure of one engine, a check
valve is incorporated in the bleed air line from each
engine to prevent loss of pressure through the com-
pressor of the inoperative engine.
Wing ice lights allow the crew to detect ice for-
mations. Ice protection of the engine is provided by
inertial separation. Automatically cycled electro-
thermal anti-icing boots are installed on the propel-
ler blades. The engine air inlet leading edge lip is
anti-iced by engine exhaust bleed. The fresh air
inlets are located in sheltered areas and require no