SECTION III. NAVIGATION EQUIPMENT
3-3-1. VHF NAVIGATION AND INSTRUMENT LAND-
ING SYSTEM (AN/ARN-123).
The VHF navigation and instrument landing system (AN/
ARN-123) is an integrated navigation receiver consisting of
a 160 channel VOR receiver, a 40-channel localizer receiv-
er, a 40 channel glideslope receiver, and a market beacon
receiver. Each receiver operates independently. The sys-
tem consists of a control panel on the console, a receiver
on the avionics shelf, and three antennas on the fuselage.
The set includes VOR and marker beacon self-test capabil-
a. VOR/Localizer Receiver. The VOR/localizer re-
ceiver processes signals in the frequency range 108.00
through 117.95 MHz. The VOR/localizer information is pre-
sented on the course deviation bar of the HSI on the pilots
and copilots instrument panels. VOR bearing information is
displayed on the No. 2 pointer of the indicator. If the received
signal is weak or the set malfunctions, a red NAV flag will
appear on the indicator. The VOR/localizer antenna is on the
bottom of the helicopter at sta. 79.
b. Glideslope Receiver. The glideslope receiver sec-
tion of the AN/ARN-123 processes signals in the frequency
range of 329.15 through 335.00 MHz. Glideslope informa-
tion is displayed on the HSI. The set will also cause a red
GS warning flag to appear on the indicator when the re-
ceived signal is unreliable or the glideslope receiver mal-
functions. The glideslope antenna is on the forward pylon
above the windshield.
c. Marker Beacon Receiver. The marker beacon re-
ceiver is a fixed -frequency receiver (75 MHz) which re-
ceives signals from a ground marker beacon transmitter
to determine helicopter position. The audio output of the
marker beacon receiver is applied through the inter-
phone system to the headsets as a direct input (no inter-
phone control box switch setting necessary). Three
marker beacon lights are on each HSI MODE SELECT
panel. The lights are labeled MKR BCN and indicate
marker beacon passage. Also specific tones will be
heard over the interphone while flying over each beacon.
Table 3-3-1 presents the indication as each beacon is
passed. The lights are tested by momentarily pressing
any one of three lights. The marker beacon antenna is
under the fuselage is under the fuselage forward of the
forward cargo hook. Power to operate the set is from the
DC essential bus through the NAV VOR circuit breaker
on the No.1 PDP. Power is supplied by the 26-volt AC
instrument bus through the NAV VOR circuit breaker on
the No. 1 PDP.
Table 3-3-1. Marker Beacon Indicator
3-3-2. OPERATION CHECK/SELF - TEST.
This test requires an external VOR RF signal
generated by a ground station, or ramp test
Set the course indicator OBS control for a 315
degrees indication under the course index.
Move the control unit VOR/MB switch to the test
The CDI deviation needle should indicate center
The VOR/LOC flag should be buried.
The RMI should point to the 315 degrees ra-
The marker beacon lamp(s) should illuminate.
3-3-3. Controls and Function, VHF Navigation and
Instrument Landing System Set. (fig. 3-3-1)
Provides power to set
when turned from OFF.
Turning knob clock-wise
from TEST position. At
TEST, the MKR BCN
Megahertz Select Knob
Selects last two digits of
frequency in 50 -kilohertz
Adjusts audio output lev-
el of marker beacon re-
ceiver. Provides power to
the marker beacon when
turned from OFF.