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equipped aircraft.
Available tacan range and bearing information is always
displayed on the pilot and RIO BDHIs and can be
selected for display on the BUD and MFDs. The tacan
data supplied to the MCS can be used for a one-fix
update ofthe INS and SAHRS, continuous update of the
system navigation solution, or for steering. The
AN/URC-107 (JTIDS) tacan requires the selection of
DATA SE., NORM, or POLL on the JTIDS control
panel (Figure 20-4) to supply digital tacan information
to the MCS. This is required for tacan displays on the
MFD, navigation updates, and tacan steering. Refer to
paragraphs2 0.3.6.2,U pdates,2 0.3.6.3,C ontinuousP osition
Updating, and 20.3.6.5, Display Steering Modes.
The tacan has 126 X channels and 126 Y channels
available 1 MHZ apart. The tacan uses two aircraft antennas,
automatically switching between the two at 5-
second intervals until a threshold signal is received. The
AN/ARN-1 18 requires approximately 2 minutes for
warmup; AN/URC-107 (JTIDS) is operational once tacan
self-test is complete. If stable range and bearing
indications are not available after this time, tune another
station or check circuit breakers.
Note
JTIDS tacan has shown reduced receiver
sensitivity on channel 83. Use of channel
83Y (G/Aand A/A) and 83X (A/Aonly)may
not receive accurate information outside 40
miles.
The tacm has a memory feature that allows tracking
to continue uninterrupted by momentary loss of received
signals. A range signal that has been tracked for at least
10 seconds will be retained in memory for 13 to 17
seconds after signal loss; a bearing signal tracked for at
least 15s econdsis retainedf or 2 to 4 secondsa fter signal
loss. This feature allows for automatic antenna switching
without loss of tacan outputs.
If the signal Born a tacan station becomes unreliable
or is lost for more than memory time, then the
tacan switches to self-test automatically. This may
cause the BDHI relative bearing to be 270’ for 2 to 4
seconds. If the signal is not acquired during the selftest,
the BDHI bearing pointer will continuously slew
in a counterclockwise direction and the TEST light on
the tacan control panel will light. If the light remains
NAVAIR 0%F14AAD-1
on, a failure is indicated and tacan information should
be disregarded. As in all tacan sets, undetected failures
can occur, so information provided by the tacan should
becross-checkedwithotheravailablenavigationinformation.
The AN/ARN-118 tacan uses 115 Vat from the ac
essential No. 2 bus through circuit breaker 3D5,28 Vdc
6om dc essential bus No. 2 via circuit breaker 8E7, and
26 Vat Born the 26-volt essential bus through circuit,
breaker 3D4. In addition to the power and circuit breakers
used by the AN/ARN- 118, the ANKIRC- 107 tacan
also requires 115 Vat from essential No. 2 bus through
circuit breaker 4D3 and 4D4. Refer to Chapter 2 for the
alphanumeric circuit breaker listing.
20.1.9.1 Tacan Controls and Indicators. Two
identical TCN control panels (Figure 20-4), one in each
cockpit, are provided to permit either crewmember to
operate the tacan. To determine which crewmember
controls the tacan, each cockpit has an alternate action
TACAN CMD pushbutton that illuminates either PLT
or IWO to show which cockpit has command. Both
buttons allow each crewmember to either give or take
command of the tacan. A BDHl in each cockpit provides
range and bearing to a tuned tacan station. Other tacan
displays may be selected.
20.1.9.2 Tacan Testing. Tacan testing includes
continuous monitoring and commanded self-test. Continuous
monitoring checks certain internal timctious of
the tacan on a continuous basis. Failure of one of these
checks causes the TEST light on the TCN panel to illuminate.
Commanded self-test is either manually or automatically
initiated. The TEST button is a momentary
action pushbutton switch that is pressed to place the
tacan into the commanded self-test mode manually. The
test may be accomplished in all operating modes. Commanded
self-test interrupts normal operation for a 22-
second cycle and provides a high-confidence test of the
tacan except for the antennas.W hen TEST is selected
in T/R, a power check is initiated for the transmitter,
receiver, distance, and beating circuita. The BDHI hearing
pointer should swing to 270’ in 2 to 7 seconds and
the range OFF flag should appear. After approximately
7-seconds, the BDHI bearing pointer should swing to
180’ and thenO FF flag should disappear.T he distance
indicatorshouldread 000.0 nm. The BDBIshould return
　
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