TM  55-1510-220-10 extinguishes.  Roll steering output returns to normal limit of 25 degrees. (3) Data   display,   left   and   right:   Composed   of lights  which  illuminate  to  display  numbers,  decimal  points, degree   symbols,   left   and   right   directions,   and   latitude   or longitude directions. (4) INSERT/  ADVANCE/  HI  PREC  key.  Allows insertion of loaded data into computer.  Enters displayed data into INS.  When pressed before pressing any numerical key, alternates display of normal and high precision data. (5) ALERT light.  Illuminates amber to alert pilot 1.3  minutes  before  impending  automatic  course  leg  change. Extinguishes   when   switched   to   new   leg,   if   AUTO-MAN switch  is  set  to  AUTO.    Flashes  on  and  off  when  passing waypoint,  if  AUTO-MAN  switch  is  set  to  MAN.    Light  will extinguish   if   AUTO   is   selected   or   if   a   course   change   is inserted. (6) WARN  light.    Lights  red  to  alert  pilot  1  .;S self-test  circuits  have  detected  a  system  fault.    illumination may   be   caused   by   continuous   or   intermittent   condition. Intermittent  conditions  light  until  reset  by  TEST  switch.    If continuous   condition   does   not   degrade   attitude   operation, light goes out when mode selector is set to ATT. (7)     Keyboard.    Consists  of  10  keys  for  entering load data into data and TO-FROM displays. N, S, E.  and W (on  keys  2,  8,  6,  and  4)  indicate  direction  of  latitude  and longitude.  TAC and DISP (on keys 7 and 9) enable loading and  display  of  TA(.'AN  station  data.    MV/P  and  DISP  (on keys  3  and  9)  are  associated  with  loading  and  display  of magnetic    variation,    magnetic    heading,    and    the    pattern steering   mode.      R/B   and   DISP   (on   keys   5   and   9)   are associated with loading and display of UTM coefficients and waypoint move parameters. (8) CLEAR  key.    When  pressed,  illuminates  and erases  data  loaded  into  data  displays  or  FROM-TO  display. Used  to  cancel  erroneous  data.    After  clearing,  data  loading can be resumed. (9) WYPT   CHG   key.      When   pressed,   enables numbers     in     FROM-TO     display     to     be     changed.          If L.JSERT/ADVANCE   key   is   pressed,   computer   will   use navigation   leg   defined   by   new   number   in   all   navigation computations.    If  INSERT/  AD)VANCE  key  is  not  pressed, computer    will    .continue    using    original    numbers    in    all navigation computations; but distance/time information, based onnew leg, may be called up and read in data displays (in  case  of  waypoints).    When  not  in  TACAN  mix  mode, TACAN   station   number   is   inserted   to   display   DIS/TIME information. (10) AUTO-MAN   TEST   switch.      This   is   a   dual purpose control.  When the knob is pressed inward, the TEST switch  function  is  engaged.    When  the  knob  is  rotated  to either  the  AUTO  or  MAN  setting,  the  control  serves  as  a selector between those modes. (a) AUTO.  Selects automatic leg switching mode.  Computer switches from one leg to the next-whenever waypoint in TO side of the FROM-TO display is reached. (b) MAN.      Selects   manual   leg   switching mode.  Pilot must make waypoint changes manually. (c) TEST.    When  pressed,  performs  test  of INS    lights    and    displays,    remote    lights    and    indicators controlled by INS, and computer input/ output operations. Used with other controls to activate display of numerical codes  denoting  specific  malfunctions  and  resets  malfunction warning circuits. During   alignment,   activates   the   HSI   test.      Continued pressing  of  switch  provides  constant  INS  outputs  to  drive cockpit displays in a predetermined fashion. NOTE The   INS   can   provide   test   signals   to   the Horizontal   Situation   Indicator   (HSI)   and connected  displays.    Pressing  TEST  switch during STBY, ALIGN, or NAV modes will cause all digits on connected digital displays to  indicate  "8's"  and  illuminates  the  HSI and   ALERT   lights.      Additional   HSI   test signals are provided when INS is in ALIGN and   the   data   selector   is   at   any   position other    than    DSRTK/STS.        Under    those conditions, pressing TEST switch causes the HSI  to  indicate  heading,  drift  angle,  and track angle error all at "0°" or "30°".  At the   same   time,   cross   track   deviation   is indicated at "3.75" nautical miles (one dot) right  or  left  and  INS-controlled  HSI  flags are retracted from view. Output  test  signal  are  also  supplied  to the autopilot when INS steering is selected. Rotating AUTO-MAN switch to Change 5  3-48