When power is first applied, the radar
will be in the WAIT mode for 45
seconds to allow the magnetron to
Weather Radar Modes of Operation.
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.
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 aircraft's wheels. The forced standby
mode is a safety feature that stops the radar from
transmitting on the ground to eliminate the microwave
radiation hazard. In the forced standby mode, the
transmitter and antenna scan are both inhibited and the
Forced standby may be overridden (restoring normal
operation) by simultaneously depressing both range
switches on the radar control panel.
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
categorizing 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 compensation technique (RCT) or target alert
(TGT) is selected. In the weather detection mode
precipitation is displayed in five levels as black, green,
yellow, red, and magenta.
In order to permit the user to interpret the display,
targets are displayed in various colors. Each color
represents a specific target intensity. The relationship
between the colors on the display and the national
weather service video integrated processor (VIP) level is
compensation technique may be used in the WX mode to
compensate 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. Depressing the RCT pushbutton switch on the
weather radar selects 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 variable gain from operating.)
Ground mapping mode. Ground mapping
mode is selected by setting the radar system mode
selector 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
altered to pro vide 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
display patterns that indicate water regions, coast lines,
hilly or mountainous regions, cities, or even large
Fault monitoring. Critical functions in the
receiver/transmitter/antenna are continuously monitored.
3-32. LIGHTNING SENSOR SYSTEM (LSZ-850).
The lightning sensor system is to be
avoidance, not weather penetration.
The lightning sensor system (LSS) is used to detect
and locate areas of lightning activity within a 100 nautical
mile radius around the aircraft. The system provides the
operator with a visual display of the position and rate of
occurrence of the lightning activity on the EHSI. The
lightning sensor system detects both visible and high
discharges (lightning) indicating areas of turbulent activity.
After evaluating the LSS display, and its relation to
precipitation as indicated by the weather radar display,
the operator can effectively plan the proper course to
avoid hazardous weather. The lightning sensor system
consists of a receiver/processor, an antenna, a mode
selector switch (located on the radar control panel, fig. 3-
29), and the pilot's and copilot's EHSI. The system is
powered by a 2-ampere circuit-breaker placarded LSS,
located on the overhead circuit breaker panel (fig. 2-9).
Because the system is a passive device (it does not
transmit), it can be operated safely on the ground.
Weather in all directions around the aircraft may be
monitored, even before starting engines.
Lightning Sensor System Mode Selector Switch
OFF. Disables lightning sensor system.
SBY. In the standby (SBY) mode, lightning
data is not displayed. However, the receiving and
processing equipment is active and lightning strikes are
being counted and accumulated.