TM 55-1520-228-10
Change 11 3-32.1
3-67.4. OPERATING PROCEDURES –
RADAR 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) Lower right knob – Press. The pointer and
digital display should read 1000 feet ($ 100). Also, the
HI indicator on the radar altimeter should be illuminated.
Release the knob. The reading should extinguish.
(2) Lower left knob – Adjust clockwise until the
LO bug is positioned “above” (greater in altitude than)
the pointer. A periodic audio warning “ALTITUDE LOW-
TOO-LOW” should be heard in all headsets. Also, the
LO indicator on the radar altimeter should be illumi-
nated.
(3) Master ICS volume control – Rotate on each
respective ICS unit. The audio warning volume should
fluctuate. The audio warning volume level can also be
altered by momentarily pressing the Push-To-Test
(PTT) knob (lower-right) on the radar altimeter itself af-
ter the voice warning has been initiated. Depress the
PTT knob once. The audio warning volume should be
1/2 the initial level. Depress the PT knob a second time.
the audio warning message should be disabled. Once
the volume level is reduced 1/2 initial level, the audio
warning volume level cannot be changed (except by
adjusting the master ICS volume control) or once dis-
abled it cannot be brought back.
(4) Lower left knob – Adjust counterclockwise
until the LO bug is “below” the pointer, then adjust the
knob clockwise until the LO bug is positioned “above”
the pointer again. The “ALTITUDE LOW - TOO LOW”
audio warning should be again heard at its initial “FULL”
volume level.
(5) Lower knob – Adjust counterclockwise until
the LO bug is “below” the pointer, (but not quite to the
OFF position). The warning audio should cease. The LO
indicator should be extinguished.
(6) Lower right knob – Depress and hold to put
the Radar Altimeter into the test mode. A periodic “ALTI-
TUDE HIGH-CHECK ALTITUDE” should be heard in all
headsets. Also, the HI indicator on the radar altimeter
should be illuminated.
(7) Push-To-Test knob – Release. The warning
audio message should cease. The HI indicator should
be extinguished.
c. Stopping Procedure. LO SET control knob –
Rotate counterclockwise from LO.
3-68. RADAR SIGNAL DETECTING SET
(AN/APR-39A(V)1).
Refer to TM 11-5841-294-12.
3-68.1. DESCRIPTION – RADAR SIG-
NAL DETECTING SET (AN/
APR-39A(V)1).
a. Description. The radar signal detecting set AN/
APR-39A(V)1 provides the pilot with visual and audible
warning when a hostile fire control threat is encoun-
tered. The equipment responds to hostile fire-control
radars but non-threat radars are generally excluded.
The equipment also receives missile guidance radar
signals and, when the signals are time-coincident with
a radar tracking signal, the equipment identifies the
combination as an activated hostile surface-to-air mis-
sile (SAM) radar system. The visual and aural displays
warn the pilot of potential threat so that evasive maneu-
vers can be initiated.
b. Function.
(1) The AN/APR-39A(V)1 receives, processes
and displays pulse type signals operating in the C-D and
H-M radio frequency bands. The emitters that it pro-
cesses and displays are derived from the emitter identi-
fication data (EID) contained in the user data module
(UDM) that is inserted in the top of the digital processor.
In normal circumstances the processor is classified con-
fidential if a classified UDM is installed.
(2) The UDM contains the electronic warfare
threat data that makes up the specific library for a specif-
ic mission(s) or a geographical location (it is theater-
ized). When a match of the electronic warfare data
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