TM 1-1520-218-10 3C-168 Figure 3C-119.  Pilot Position Page Table 3C-80.  Pilot Position Page Procedure NO. FUNCTION/DESCRIPTION 1 Pressing  PSN  function  key  will  access  the pilot position page. 2 Computed   magnetic   variation   at   present position. 3 This  line  select  key  is  non-operational if a computed wind speed is available or if the FMS is displaying an INU wind.   Otherwise,  the  following  three  actions  will occur. 1.  Selection    with    a    valid    entry    in    the scratchpad will enter the wind. 2.  Selection  with  an  empty  scratchpad  will copy the wind entry into the scratchpad. 3.  Selection with a  – in the scratchpad will set the wind speed to 0 knots. 4 Track displays MAG track. 5 Navigation source selected on pilot/copilot lateral steer pages. The status and validity of the navigational source is   indicated   on   the   title   lines   of   the   Pilot   Position pages.      Table   3C-81  lists  the  indications  and  their meanings.          Any     automatic     downgrading     of     the navigation source is annunciated on the CDU. A  NAV  error  annunciation  and/or  the  HSI  flag are  provided  when  either  the  status  of  the  selected navigation   sensors   has   degraded   or  the  95%  error exceeds  a  threshold  determined  by  the  current  flight plan   guidance   mode;   EN   ROUTE,   TERMINAL,   or APPROACH.        When    these    alerts    are    provided, examine   the   current   state   of   the   GPS   navigation solution   and   compare   the   solution   to   the   other   on- board   navigation   systems.      If   necessary,   select   a different    navigation    sensor    to    provide    continued guidance of the aircraft. (a)   GPS Display.   The GPS INAV page shows   the   present   position   output   from   the   GPS receiver.  It also shows a 95% error figure of merit for the probable system accuracy, given the current GPS satellite   navigational   quality   (satellite   tracking   state and    geometry)    as    shown    in    Figure    3C-120    and Table 3C-82.    If  GPS/A/H  is  indicated  on  the  title  line, the  FMS-800  is  using  airspeed  and  heading  sensor inputs  to  smooth  the  GPS  data.    This  is  required  to have  a  valid  bank  (roll)  command  output  to  the  flight director and autopilot. The  MODE  indicates  the  current  GPS  receiver tracking/aiding mode of INIT, TEST, or NAV/PVA. The STATE indicates the lowest tracking state of the  four  primary  satellite  tracking  channels:  STATE  1 is    acquisition,    STATE    3    is    code    track    only    (in jamming),  and  STATE  5  is  code  and  carrier  lock  (no jamming). The    number    of    satellites    being    tracked    for primary  navigational  purposes  is displayed.  Normally four satellites are tracked to provide a fully determined position   (a   four   dimensional   position   requires   four satellites).    Less  than  four  may  result  in  GPS's  data being invalid. Table 3C-81.  Display of Navigation Mode on Position Pages SELECTED NAV SOLUTION DISPLAYED MODE CONDITIONS FOR DISPLAY GPS GPS/A/H GPS navigation data is smoothed with airspeed and heading GPS GPS/ - /H GPS   navigation   data   is   being   smoothed   with   GPS   groundspeed   and heading GPS GPS/ - / -   GPS is not being smoothed with airspeed and heading data GPS - - - /A/H GPS is invalid; FMS is dead reckoning with airspeed and heading data MODEL MODEL The   model   aircraft   function   is   providing   the   navigation   solution.      This function is available only while on the ground.