TM 55-1510-220-10 (j) Waypoint   key.      The      waypoint   key. placarded WP, is used to enter and examine waypoint data. (k) Mark key.  The  MARK  key is used for MARKand FREEZE functions. (2) GPS  key,  load,  and  zeroize  panel  controls. indicators, and functions (fig.  3-25B). (a) GPS   zeroize      switch.      Actuating   the guarded switch.  placarded ZEROIZE GPS, will declassify the GPS receiver. (b) GPS    key  connector.      Connects  GPS key. (c) Load  switch.    This  pushbutton  switch initiates loading process. (d) Load status indicator light.  Illuminates to indicate load status. (e) Dust  cap.    Covers  GPS  key  connector when not in use. c. GPS System Modes of Operation. (1) Off  mode.    When  the  PULL  OFF  mode  has been  selected.    power  is  removed  from  the  system.    except panel lighting. NOTE Critical  memory  and  other  circuits  which cannot  be  turned  off  remain  powered  by batteries in the receiver. (2) Initialize  mode.    When  the  INIT  (initialize) mode  has  been  selected,  position  and  time  estimates  can  be entered  via  the  keypad.    Waypoint  data  may  be  entered  and examined.      and   option   selections   made.      No   navigation functions can be performed.  If the INS is in NAV mode.  the INS   position   from   the   INS   and   altitude   from   the   pilot's encoding  altimeter  will  be  displayed  on  the  CDI.  This  data will be used by the GPS for initial position and altitude. (3) Navigation   mode.      Selection   of   the   NAV (navigation)  mode  enables  normal  GPS  functions  (satellite tracking and navigation).  including data transfer to and from the INS. (4) Test   mode.      Selection   of   the   PULL   TEST mode initiates a full command test of GPS user equipment for line replaceable unit (LRU) fault identification and isolation. d. GP.S Normal Operation. (1) GPS   start   procedures.      The   GPS   must   be initialized prior to being used for navigation.  There are three types of start: normal, quick, and cold.  A position estimate, time estimate, and almanac (or ephemeris) data are required for  a  normal  start.    A  quick  start  uses  stored  position,  time, and recent ephemeris information.  A cold start is used only when the GPS is unable to perform a normal startup. (a) GPS normal start. 1. Mode  selector  switch  INIT.  When built-in-test is complete the display will show   data   corresponding   to   the   data selector switch position. NOTE Data   display   will   not   be   illuminated   for about    30    seconds    after    GPS    has    been turned    on.        Ensure    that    the    display brightness  control  has  been  set  to  the  full clockwise    position    to    receive    the    INIT display, then adjust as desired. NOTE If the GPS has been OFF for more than 30 seconds when INIT mode was selected. the set   will   perform   the   initial   built-in-test which takes approximately 30 seconds. 2. Data     selector     switch     POS.     If ENTER    POS    message    is    displayed press line select key 3 next to message. Position must be entered. 3. Displayed   position   Check.   Verify or    enter    new    updated    position    and altitude as required . 4. Data selector switch TRKGS. Verify  correct  track  and  groundspeed are displayed. If not valid, enter correct values. 5. Slew  key  Press.    Check,  verify,  or enter   current   time,   year,   and   day   of year on page 2. Change 5       3-76C