TM 1-1510-225-10 3C-54 If  the  system  fails  any  of  the  internal  tests,  an error  message  will  display  indicating  what  test  failed and   what   functions   may   be   inoperative.      In   most cases,  all  other  systems  will  continue  to  operate.    If continued operation is possible, the message, PRESS ANY KEY TO CONTINUE, will display. When    initially    turned    on,    the    system    may complete its self-test  program  before  the  CRT  comes on.    In  that  case,  it  is  possible  that  the  first  message that  will  be  seen  is  the  main  menu.    This  is  normal operation. If  the  weather  screen is selected immediately, it is  possible  the  advisory  message  FLAG  will  display where heading information is normally displayed.  This usually means the gyro system has not yet come up to speed.        FLAG    should    be    replaced    with    heading information momentarily. (2)   Main   Menu.    The  main  menu  provides access  to  the  two  weather  mode  views  and  additional system functions, including checklists, time/date information,  options,  and  navaid  display.  To  select  a specific   menu   item,   press   the   NEXT  button  on  the display   until   the   desired   item   is   highlighted.      Then press the GO button to view the selected menu item. (3)   Weather   Modes.      Two   weather   mode views  are  available  from  the  main  menu  by  pressing either the 360°  button or the  120°  button.  The symbol ®  means  go  to.    When  the   weather  mode  is  initially selected,   it   will   always   be   in   the   200   nm   range.   Pressing the button beside the range setting will cycle through the additional range selections from 200 nm to 100 nm to 50 nm to 25 nm and back to 200 nm.  The 25  nm  range  is  indicated  by  a  solid  ring  to  advise  of close proximity to potential thunderstorms.  Either view can  be  selected  from  the  main  menu  or  the  opposite view.    When  changing  from  one  view  to  another,  the range remains constant. The  120°  view  provides  an  expanded  view and therefore   thunderstorm   information   is   displayed   in greater detail.  Refer to Figure 3C-23. Press the   CLEAR  button  to  erase  all  weather data   from   the   display   and   system   memory.      The intensity  of  a  thunderstorm  can  be  identified  by  the speed  with  which  the  discharge  points  appear.    The system    continually    receives    and    processes    new electrical    discharge    information.        Monitor    this    by pressing the  CLEAR  button  often.    The  more  intense the storm, the faster the discharge points reappear. Figure 3C-23.  120° Weather Mode Multiple  discharges,  which  appear  as  clusters, are indicative of thunderstorm activity.  A large number of discharge points indicate a faster rate of occurrence and,  therefore,  a  more  severe  thunderstorm.    Fewer discharge points indicate a smaller, but not  necessarily,   weaker,   cell.      Thunderstorm   conditions change   rapidly   and   monitoring   their   activity   over   a period    of    time    by    use    of    the    CLEAR    button    is recommended.      Any   grouping   of   discharge   points within    the    25    nm   range   is   cause   for   immediate avoidance. The  Stormscope  System  should  never  be used to attempt thunderstorm penetration.   The FAA and AIM recommend avoiding by at least 20 miles any thunderstorm identified  as  severe  or  giving  an  intense radar echo. CAUTION Persistent clusters of two or more discharge  points  indicate  thunderstorms. There are several atmospheric phenomena that  can  cause  isolated  discharge  points.   Clusters  of  two  or  more  discharge  points indicate   thunderstorm   activity   when   they re-appear   persistently   after   clearing   the screen. Additionally, should the heading stabilization fail, it is necessary to press the CLEAR button for properly oriented data following an aircraft heading change. WARNING