TM 1-1510-224-10 NOTE When power is first applied, the radar will   be   in   the   WAIT   mode   for   45 seconds   to   allow   the   magnetron   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 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 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 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 shown in table 3-12. Rain echo attenuation 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.) (4) 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 structures. (5) Fault  monitoring.    Critical  functions  in  the receiver/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 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 energy invisible electromagnetic and electrostatic 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. a. Lightning  Sensor  System    Mode  Selector  Switch (fig.  3-29). (1) OFF.  Disables lightning sensor system. (2) 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. 3-84