The GPU shall be adjusted to
regulate at 28 volts maximum to
prevent damage to the aircraft.
DC External Power Source. External DC power
can be applied to the aircraft through an external power
receptacle on the underside of the right wing leading
edge just outboard of the engine nacelle. The
receptacle is installed inside of the wing structure and is
accessible through a hinged access panel. DC power is
supplied through the DC external plug and applied
directly to the battery bus after passing through the
external power relay. Turn off all external power while
connecting the power cable to, or removing it from, the
external power supply receptacle. The holding coil
circuit of the relay is energized by the external power
source when the BATT switch is in the ON position. The
GPU shall be adjusted to regulate at 28 volts maximum
to prevent damage to the aircraft battery.
Security Keylock Switch. The aircraft has a
security keylock switch (fig. 2-18) installed on the
overhead control panel, placarded OFF ON. The switch
is connected to the battery relay circuit and must be ON
when energizing the battery master power switch. The
key cannot be removed from the lock when in the ON
Circuit Breakers. The overhead circuit breaker
panel (fig. 2-26) contains circuit breakers for most
aircraft systems. The circuit breakers on the panel are
grouped into areas which are placarded as to the
general function they protect. A DC power distribution
panel is mounted beneath the floor forward of the main
spar. This panel contains higher current rated circuit
breakers and is not accessible to the flight crew under
2-73. AC POWER SUPPLY.
Single Phase AC Power Supply. AC power for
the aircraft is supplied by inverter units, numbered #1
and #2 (fig. 2-23) which obtain operating current from
the DC power system. Both inverters are rated at 750
volt-amperes and provide single phase output only.
Each inverter provides 115 volt and 26 volt 400 Hz AC
output. The inverters are protected by circuit breakers
mounted on the DC power distribution panel mounted
beneath the floor. Controls and indicators of the AC
power system are located on the overhead control panel
and on the caution/advisory annunciator panel.
AC Power WARNING/CAUTION Lights. Two
MASTER/CAUTION lights and the illumination of an
INVERTER indicates an inverter failure.
Instrument AC Light. A red warning light,
located on the warning annunciator panel, placarded
INST AC, will illuminate if all instrument AC busses
Inverter Control Switches. Two switches (fig.
2-18), placarded INVERTER #1 and #2 on the overhead
control panel give the pilot control of inverters single-
phase AC power.
Volt-Frequency Meters. Two volt-frequency
meters (fig. 2-18) are mounted in the overhead control
panel to provide monitoring capability for both 115 VAC
buses. Normal display on the meter is shown in
frequency (Hz). To read voltage, press the button
located in the lower left corner of the meter. Normal
output of the inverters will be indicated by 115 VAC and
400 Hz on the meters.
Three Phase AC Power Supply. Three phase
AC electrical power for operation of the inertial
navigation system and mission avionics is supplied by
either of two DC powered 3000 volt-ampere solid state
three phase inverters (fig. 2-24).
Three phase inverter control switch. A
three position switch placarded #1 MISSION INV, OFF,
#2 MISSION INV, located on the mission control panel
controls three phase inverter operation.
Three phase volt-frequency meter. A
three phase volt/frequency meter, mounted on the
mission control panel, monitors output of the selected
three phase inverter. Frequency (Hz) is normally
displayed on the meter. To read voltage press button
located in the lower left corner of the meter.
Three phase loadmeter. A three phase
loadmeter, mounted on the mission control panel,
monitors inverter output level.
Three phase AC off annunciator light. An
indicator light placarded 3( AC OFF, located on the
mission annunciator panel indicates that three phase AC
power is not being supplied.
Three phase AC external power. External
three phase AC power for operation of the inertial
navigation system or mission equipment, can be applied
to the aircraft through an external power receptacle
located on the underside of the left wing leading edge
just outboard of the engine nacelle. The receptacle is
installed inside the wing structure and is accessible
through a hinged access panel. The AC electrical
system is automatically isolated from the external power
source if the external power is over or under voltage,
over or under frequency, or has an improper phase