3-82 Change 3
TEST. Selection of TEST position selects
test mode and puts a test pattern on the screen to verify
system operation. TEST will be annunciated on the
EHSI in the radar mode field. TEST mode is inhibited
when system is in forced standby mode.
(9) Radar receiver gain control. This control (plac-
arded GAIN, MIN - MAX) is used the adjust receiver gain
when gain is variable. Pulling out on gain control makes
gain control variable. A fully automatic gain control is
provided when the gain control is in the preset (pushed
b. Weather Radar Normal Operation. Radar turn-on
1. Radar system mode selector switch - OFF.
2. Radar receiver gain control - Preset (pushed
3. Antenna tilt angle control - +15 degrees.
4. Weather (WX) pushbutton selector switch (dis-
play controller) - Depress to select weather
display mode on the EHSI.
5. Radar mode selector switch - SBY or TEST.
When power is first applied, the radar will be in
the WAIT mode for 45 seconds to allow the mag-
netron to warm up.
c. Weather Radar Modes of Operation.
(1) Standby mode. When SBY has been selected
with the radar system mode selector switch, the radar
antenna will be stowed in a tilt-up position and will be
neither scanning nor transmitting. Standby should be
selected any time it is desirable to keep power on the
system without transmitting.
(2) Forced standby. Provisions are included in the
weather radar controller to place the system into the
forced standby mode when the radar is operating and
weight is on the aircrafts wheels. The forced standby
mode is a safety feature that stops the radar from trans-
mitting on the ground to eliminate the microwave radi-
ation hazard. In the forced standby mode, the transmitter
and antenna scan are both inhibited and the memory
Forced standby may be overridden (restoring normal
operation) by simultaneously depressing both range
switches on the radar control panel.
(3) Weather detection mode. Normal weather
detection mode is selected by placing the radar system
mode selector switch to the WX position, and selecting
WX on the display controller. To assist the pilot in catego-
rizing storms, the radar receiver gain is calibrated in the
WX mode with the GAIN control in the preset position.
The radar is not calibrated when variable gain is being
used. Calibration is restored if rain echo attenuation com-
pensation technique (RCT) or target alert (TGT) is se-
lected. In the weather detection mode precipitation is
displayed in five levels as black, green, yellow, red, and
In order to permit the user to interpret the display, tar-
gets are displayed in various colors. Each color repre-
sents a specific target intensity. The relationship
between the colors on the display and the national
weather service video integrated processor (VIP) level is
shown in table 3-12. Rain echo attenuation compensa-
tion technique may be used in the WX mode to compen-
sate for the attenuation of the radar signal as it passes
through a storm. It does this by increasing or decreasing
the gain of the receiver as weather is detected. Depress-
ing the RCT pushbutton switch on the weather radar se-
lects and deselects the rain echo attenuation
compensation technique (REACT) circuitry and selects
and deselects the blue field display which indicates that
the receiver is at maximum gain and the reference levels
are at final values. Any returns detected beyond this point
are displayed as magenta (Selecting RCT prevents vari-
able gain from operating).
(4) Ground mapping mode. Ground mapping
mode is selected by setting the radar system mode se-
lector switch to the GMAP position. The TILT control is
then used to tilt the antenna down until the desired
amount of terrain is displayed. The degree of tiltdown will
depend upon the aircraft altitude and the selected range.
In the GMAP mode the receiver characteristics are al-
tered to provide equalization of ground-target reflection
versus range. As a result, leaving the gain control in the
depressed (preset) position will generally provide the
desired mapping display. However, the pilot may desire
to decrease the gain manually by selecting manual gain
control and rotating the GAIN control. With experience,
the pilot will develop the ability to interpret the color dis-
play patterns that indicate water regions, coast lines, hilly
or mountainous regions, cities, or even large structures.
(5) Fault monitoring. Critical functions in the re-
ceiver/transmitter/antenna are continuously monitored.
3-32. LIGHTNING SENSOR SYSTEM (LSZ-850).
The lightning sensor system is to be used for
hazardous weather avoidance, not weather pen-