INDICATORS
On SNs 24-130 through 24-229, and 25-003
through 25-064, three amber inverter warning
lights are located on the switch panel or the
glareshield. If an inverter fails, the respective
warning light illuminates. If the inverter switch
is OFF, the inverter fail light is extinguished.
OPERATION
SNs 23-003 through 24-129
AC power is normally provided by the main
inverter. A standby inverter is also installed to
supply AC power in case of a main inverter fail-
ure. AC output from the main inverter is ap-
plied via the inverter switching relay to a
26-VAC stepdown transformer and to the pri-
mary and secondary buses. The radar system
is operated by the standby inverter exclusively
when the main inverter and the radar are both
turned on. The 26-VAC stepdown transformer
supplies voltage to the AC instrument bus.
The primary and secondary buses are con-
nected by the AC bus-tie circuit breaker.
Emergency Operation
In case of a main inverter failure, the inverter
switch must be set to standby. With the in-
verter switch in this position, the standby in-
verter relay and the inverter switching relay
are energized. This allows the standby inverter
to supply AC voltage to all systems with the
exception of the radar. The radar is inopera-
tive when the switch is in the standby position.
Buses—Primary and Secondary
The primary and secondary AC buses are in-
terconnected by the AC bus-tie circuit breaker.
The primary AC bus powers the No.1 vertisyn
and directisyn yaw damper, AC voltmeter, and
the radar gyro phase detection. The secondary
bus powers the No. 2 vertisyn and directisyn,
nosewheel steering, cabin pressurization, and
sometimes fuel quantity.
Stepdown Transformers
The stepdown transformers, located on the
forward side of frame 28, reduce a portion of
the 115 VAC to 26 VAC. The 26 VAC is used
for the antiskid test (SNs 24-112 and subse-
quent), oil pressure gages, EPR gages, and
fuel flow on SNs 23-003 through 23-069.
Inverter Switching Relay
The inverter switching relay, located in the tail
compartment, is energized when the inverter
switch is set to STANDBY. When energized, the
relay allows AC voltage from the standby in-
verter to be distributed to the AC equipment.
Indication
The AC voltmeter displays the voltage for the
selected inverter.
SNs 24-130 through 24-229,
and 25-003 through 25-063,
except 25-061
AC power for the pilot’s flight instruments is
provided by the primary inverter while the
copilot’s instruments are powered by the sec-
ondary inverter. The radar is powered by the
standby inverter. A switching network allows
the standby inverter to automatically supply
115 and 26 VAC to the bus of a failed primary
or secondary inverter. An indicator light above
the inverter switch (green on SNs 24-130,133,
and 135 through 138) indicates that the in-
verter is on. An amber indicator light on all
other Learjets is located either above the in-
verter switch or on the glareshield warning
lights panel. It indicates that the inverter has
failed when the control switch is in ON. The
AC voltmeter selector switch, installed just
above the AC voltmeter, is used to monitor the
115-VAC output of the inverters.
2A-20
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
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