TM 1-1510-223-10 3-82           Change 3 (f) 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 in) position. b.   Weather Radar Normal Operation. Radar turn-on procedure. 1.   Radar system mode selector switch - OFF. 2.   Radar receiver gain control - Preset (pushed in) position. 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. NOTE 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 aircraft’s 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 erased. 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 magenta. 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). WARNING The lightning sensor system is to be used for hazardous weather avoidance, not weather pen- etration.