TM 1-1520-218-10 3C-171 mission  duration  is  entered  in  days  and  defines  the expected  length  of  an  aircraft  mission  requiring  GPS keys.  If more keys are loaded into the GPS receiver than are needed, the entry of duration will zeroize the excess  keys.    If  duration  exceeds  the  availability  of keys,   the   FMS   will   annunciate   the   need   to   load additional keys.  The duration displayed on the page is the  current  duration  of  the  keys  loaded  into  the  GPS receiver. NOTE When the GPS receiver is configured for Y- Only mode and no keys are loaded into the GPS     receiver     to     decrypt     the     satellite telemetry, RAIM processing is disabled and RAIM protection will be unavailable. The  SA/AS  mode  selection  allows  the  operator to select between a mixed mode satellite constellation with  both  keyed  and  unkeyed  satellite  transmissions, or   restrict   the   receiver   to   Y -only   keyed   satellites, excluding the use of satellites not currently keyed for P(Y) code encryption. s.    Navigation Radio Information. (1)   Navigation   Radio   Information   Overview.   The   FMS-800  provides  navigation  radio  information upon valid entry of an airport identifier.  The crew may access  the  Navigation  Radio  Information  page via the NAV function key on the CDU.  Refer to Figure 3C-123 and Table 3C-85. Selection   of   the   airport   identifier,   with   a   valid airport  ID  in  the  scratchpad  and  loaded  on  the  data cartridge, will load the airport navigation information of that airport from the data cartridge.  The entered ID will also be entered on the Communications Radio page. (2)   Navigation Radio Information Page Functionality.      Data   lines   2   through   4   display   the following data. 1.   The    name    of    the    approach    which includes  the  type  of  NAV  aid  and the runway.    The  possible  types  of  NAV aids are ILS, LOC, Back Course (BC) and  for  an  LOC,  BC,  Localizer  type Directional   Aid   (LDA),   or   Simplified Directional Facility (SDF). 2.   The frequency of the NAV aid. 3.   The  NDB  frequency  associated  with the    approach,   i f    any.        The    NDB frequency     is     the     frequency     of     a compass  locator  at  the  outer,  middle, or inner marker beacons. Figure 3C-123.  Navigation Radio Information Page Table 3C-85.  Navigation Radio Information Page Procedure NO. DESCRIPTION/FUNCTION 1 Pressing   the   function   key   NAV   will access the Navigation Radio Information page. 2 Indicates the frequency of the recommended airport navigation aid. 3 Indicates page 1 of 4. 4 The NDB frequency. 5 The frequency of the navigation aid. 6 The runway ID. 7 Type of navigation aid. 8 When    a    valid    airport    ID    is    in    the scratchpad, LS1 retrieves the navigation  information  for  that  ID  from the data cartridge. 9 The airport ID. (3)   Vertical  Scrolling.    Vertical  scrolling  has the following characteristics. 1.   Will access additional approach frequency data for other runways and wrap around in both directions if more than one page of information exists. 2.   Data   line   1   will   remain   fixed   during scrolling. The  frequencies  will  be  displayed  in  groups  of three  per  page.    A  maximum  of  12  frequencies  or  4 pages may be accessed.