The system performs only the function of
weather detection or ground mapping. It
should be used nor relied upon for
Do not operate radar system, even in
standby mode, without 115-Vac, 400-Hz
power, the receiver-transmitter cooling
blower will not operate, which could result
In weather detection mode, storm intensity levels
are displayed in three bright colors contrasted against
a deep black background. Areas of heaviest rainfall
will appear in red, less severe rainfall in yellow,
moderate rainfall in green, and little or no rainfall in
displayed in cyan, are provided to facilitate evaluation
of storm cells. The cyclic function further emphasizes
the heavy rainfall areas (red) of the weather display by
flashing them approximately once per second.
Selection of the map function causes system
parameters to be optimized on the three lowest ranges
to improve resolution and identification of small targets
at short ranges. The reflected signal from various
ground surfaces is displayed as magenta, yellow, or
cyan (most-to-least reflective).
The radar system consists of three units:
Indicator, Receiver-Transmitter, and Antenna. The
indicator is mounted in the cockpit and contains all the
controls used to operate the radar. The Receiver-
Transmitter is located on the radio rack. The Antenna,
which is fully stabilized for aircraft pitch and roll, is the
avionics compartment in the nose of the aircraft.
b. Radar System Switches and Functions.
Refer to Figure 3B-140.
(1) INT / OFF. Rotary control used to turn
system on and off, and to adjust (intensity) of display.
Turn-on, STBY, and 100 will be displayed.
(2) Display Area. Refer to Paragraph 3B -33c
(3) 10 / 25 / 50 / 100 / 200 / 300. Momentary
push buttons used to select one of six ranges. For
each selected range, five range marks are displayed.
At system turn-on, 100-mile range is automatically
selected. Internal memory for range push buttons is
(4) TILT. Rotary control used to select tilt
angle of antenna beam with relation to earth (with
stabilization on) or with relation to airframe (with
stabilization off). Clockwise rotation tilts beam upward
downward 0 to 10°.
(5) AZ MK. Slide control used to either
display or not display azimuth markers at 30° intervals.
(6) STAB. Slide control used to turn antenna
stabilization ON or OFF.
(7) TGT ALRT. Slide control used to turn
target alert function ON or OFF. When enabled, the
letter T in a red rectangle is displayed to identify that
target alert function is active. Target alert is active
only when radar gain is calibrated; i.e., in WX with
GAIN PRESET and in CYC or TEST. The symbol
TGT é in a red rectangle is displayed and flashes
once each second whenever a red-level target is
detected within the target alert section (range from 10
to 160 nm and within ±7.5° of aircraft heading). Target
alert is deactivated automatically when operating
controls are restored to valid alert settings.
(8) GAIN. Rotary control with one fixed-gain
detented position, PRESET. Used to adjust sensitivity
of radar receiver, primarily to resolve nearby strong
target signals while ground mapping. Sensitivity
increases with clockwise rotation. Full counter-
clockwise rotation to detent sets gain at preset level.
When control is not in detented position, VAR is
displayed unless preset gain has been automatically
(9) FRZ. Momentary push button used to
turn freeze function on or off with alternate presses.
When freeze is selected, display is not updated with
incoming target return data. To alert pilot, FRZ label is
displayed and is flashed on and off once each second.
FRZ is automatically deactivated whenever selection
of different control settings dictate a change in
(10) TEST. Momentary push button used to
select a special test pattern to allow verification of
system operation. In test position, transmitter is not
enabled; 100-mile range and preset range gain are
automatically selected; and TEST is displayed.
(11) MAP. Momentary push button used to
select ground-mapping display; MAP is displayed.