TM 1-1520-218-10 3C-190 Figure 3C-140.  Timer Page Access and Usage Table 3C-103.  Timer Page Access and Usage Procedure   NO. DESCRIPTION/FUNCTION 1 Press   IDX   function   key   for   access   to index page. 2 Access timers page. 3 Timer 1 is counting down. 4 Timer 3 is counting up. 5 Enter    a    new    countdown    time    in    the scratchpad. 6 Set timer 3 to the new countdown time. Table 3C-103.  Timer Page Access and Usage Procedure  (Continued) NO. DESCRIPTION/FUNCTION 7 Freeze  the  timer  display  by  pressing  the LAP  line  select  keys.    The  timer  keeps running    and    an    asterisk    replaces    the arrow.      Unfreeze   the   timer   display   by pressing the LAP line select key. 8 Press  the  line  select  key  for  timer  3  to automatically  toggled  to  OFF  and  set  to the  new  time.    Press  the  line  select  key again to start the countdown. (3)   Model    Aircraft    Function.        The    model aircraft is a mission simulation capable of following all flight   plan   maneuvers   to   include   holding   patterns, vertical navigation, and intercepts.  The model aircraft can   only   be   operated   when   the   weight   on   wheels discrete  indicates  the  aircraft  is  on  the  ground.    The ability  of  the  model  to  correctly  navigate  is  limited  to the  mid-latitude  (<  70)  regions  and  airspeed  above 10 knots.      Higher   latitudes   and   low   airspeeds   may produce unexpected results in system response due to instabilities in the model. Prior to accessing the Model Aircraft page, enter the initial present position on the Start 1 page.  Access the  Model  Aircraft  page  by  pressing  the   MODEL line select     key     on     the     Index     2     page.          Refer     to Figure 3C-141  and  Table  3C-104.    Toggle the  MODE line  select  key  to   RUNNING  to  run  the  model.    All steering  displays  will  reflect  guidance  information  as though  the  aircraft  were  flying  and  executing  the  flight plan.  Toggle the  MODE line select key to  STOPPED to stop the model. The   heading/track   and   speed   values   on   the Model  Aircraft  page  will  correctly  reflect  the  current aircraft    model's    state    and    can    be    re-entered    to different  values.    The  modes  of  heading  available  are steering  (STR)  mode  and  heading  (HLD)  hold  mode.   When   STR   mode   is   selected,  the  model’s  heading changes in response to steering commands calculated to follow the flight plan.  When HLD mode is selected, the model maintains the entered heading.  Toggle the HDG  line  select  key  on  the  model  aircraft  page  to select the desired mode. Altitude  may  be  entered  to  any  desired  value.   When the desired vertical path has been captured, the model tracks the vertical flight plan.  When no altitude has been assigned, a level altitude will be maintained.