TM 55-1520-228-10
3-32 Change 11
3-64. RADAR ALTIMETER (without MWO
1-1520-228-50-52).
NOTE
Simultaneous operation of the AN/
APR-39, radar warning receiver and the
AN/APN-209 radar altimeter will cause
a strobe to appear on the AN/APR-39
CRT and an audio tone can be heard in
the headset for IGE hover.
3-65. DESCRIPTION – RADAR ALTIME-
TER.
The radar altimeter AN/APN-209 (figure 3-16) is a short
pulse, terrain tracking and altitude sensing radar system
that measures and visually indicates by pointer and digi-
tal display actual clearance in feet between the helicop-
ter and terrain over a range from zero to 1500 feet. The
indicator contains all the electronic components neces-
sary for the generation, reception, and tracking of the
radar pulses. The indicator provides precise altitude in-
dications with a manually set low-level and high-level
warning flag to warn when a predetermined low and high
altitude limit has been reached.
3-66. CONTROLS AND FUNCTIONS – RA-
DAR ALTIMETER.
Refer to figure 3-16.
3-67. OPERATING PROCEDURES – RA-
DAR ALTIMETER.
NOTE
Refer to TM 11-5841-284-23&P for
additional operating instructions. Partic-
ular attention shall be given to “Obstacle
Avoidance” as follows: The altimeter
system tracks the terrain below the air-
craft and, therefore, will not provide use-
ful information to aid in obstacle
avoidance. By the time a sufficient area
of an obstacle is within the antenna
beams so the altimeter set can display
the near object, the aircraft probably
could not be maneuvered to avoid the
object.
a. Altimeter Operation.
(1) LO SET control knob – Rotate clockwise
from OFF. Set low limit index as desired.
(2) HI SET control knob – Set high limit index as
desired.
b. Self-Test Operation.
(1) High limit index – Set to 800 feet.
(2) Low limit index – Set to 80 feet.
(3) HI SET control knob – Push and hold. Verify
pointer indicates 1000 ($100 feet), digital display reads
1000 ($100 feet), and HI level warning flag is exposed.
(4) HI SET control knob – Release. Verify point-
er indicates 0 ($5) feet, digital display reads -0 to 3 feet,
and low warning flag is exposed.
c. Stopping Procedure. LO SET control knob –
Rotate counterclockwise from LO.
3-67.1. RADAR ALTIMETER (with MWO
1-1520-228-10-50-52).
NOTE
Simultaneous operation of the AN/
APR-39, radar warning receiver and the
AN/APN-209 radar altimeter will cause
a strobe to appear on the AN/APR-39
CRT and an audio tone can be heard in
the headset for IGE hover.
3-67.2. DESCRIPTION – RADAR AL-
TIMETER.
The radar altimeter AN/APN-209 (V) (figure 3-16) is a
short pulse, terrain tracking and altitude sensing radar
system that measures and visually indicates by pointer
and digital display actual clearance in feet between the
helicopter and terrain over a range from zero to 1500
feet. The indicator contains all the electronic compo-
nents necessary for the generation, reception, and
tracking of the radar pulses. The indicator provides pre-
cise altitude indications with a manually set low-level
and high-level warning voice and flag to warn when a
predetermined low and high altitude limit has been
reached.
3-67.3. CONTROLS AND FUNCTIONS
– RADAR ALTIMETER.
Refer to figure 3-16.
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