TM 1-1510-218-10 3B-34 1.     Message Key and Annunciator 2.     Cursor Key 3.     Mode Key 4.     Sensor Key 5.     OBS/LEG Key 6.     Frequency Key 7.     Brightness Control Switch 8.     Power Switch 9.     Numeric Entry Keys 10.     Alphabetic Entry Keys 11.     ENTER Key 12.     Clear Key 13.     Hold Key 14.     Data Key 15.     Navigation Key 16.     Waypoint Key 17.     Flight Plan Key 18.     Direct Key 19.     Display Screen Figure 3B-18.  FMS Control Display Unit (KR 87) (j)    Multiple    waypoints    (waypoints    that serve as members of any combination of high and low altitude waypoints, DR/STAR's, or approach intersections). c.     Configuring   the   Data   Base.      Not   all   the worldwide  navigation  data  contained  on  the  diskette will   fit   into   the   FMS   system's   internal   data   base (memory) at one time.  It is necessary to choose which geographical regions and which navigational elements within  those  geographical  regions  are  desired  to  be loaded  at  one  time.    The  diskette  may  be  used  as often as necessary during the 28-day valid period. d.    Supplemental Data Base.  In addition to the published   navigation   data   base   the   FMS   has   an additional  nonvolatile  memory  capacity  that  may  be utilized  for  storing  waypoints,  flight  plans,  and  other user  defined  data.    This  additional  memory  can  store 100  flight  plans,  800  waypoints, and 175 user-defined navaids and airports. e.     Data Base Revision Cycle.  Every 28 days, several  days  prior  to  the  effective  date  of  the  next revision,    a    diskette    is    sent    to    each    data    base subscriber    that    includes    a    complete    new    set    of worldwide  data.    The  update should be accomplished before the effective date of the revision.  If the FMS is not in operation at 0000 GMT on the effective date, the system automatically switches to the revised data.  If the FMS is in operation at 0000 GMT on the effective date, the system automatically switches to the revised data the next time it is turned on.  If the FMS does not get  updated  with  the  latest  revision  data  prior  to  the effective date, the system will continue to function but will provide a message stating:  D/BASE OUT DATED. f. Data Base Battery.   A small battery located internally  in  the  FMS  computer  keeps  the  data  base alive when power is removed from the system.  Typical battery   life   is   6   years.      When   about   one   week   of battery life remains, the system will display a message stating: D/BASE BATT LOW. Maintenance technicians should replace the battery at this time. g.    ICAO  Identifiers.     In  order  to  access  data from the data base it is necessary to use International Civil  Aviation  Organization  (ICAO)  identifiers.    In  most cases   the   proper   ICAO   identifiers   may   be   taken directly    from    navigation    publication    such    as    high altitude    charts,    low    altitude    charts,    area    charts, approach plates, DR's, STAR’s, and other references. (1)   Airport ICAO Identifiers. Airport reference   points    are    stored    by    the    airport    ICAO identifier.    The  majority  of  airport  identifiers  have  four letters beginning with a prefix letter that corresponds to the geographic area in which it is located (for example, KJFK).      The   prefix   letter   for   the   continental   United States is "K".  The prefix letter for Hawaii and Alaska is "P".      Some   airport   identifiers   are   a   combination   of three  or  four  letters  and  numbers  such  as  3LA,  7TX6, or   M33.      Most   published   airport   identifiers   in   the continental   United   States   are   in   the   official   ICAO format.      The   exception   is   an   airport   identifier   that consists of only three letters and no numbers, such as