TM 1-1510-225-10 3A-95 If  no  descent  reference  waypoint  with  crossing altitude is programmed, the system will use the arrival airport   and   elevation,   ARP   reference   point,   not   a runway, to fix top of descent as long as an AFIS flight plan is not used. One minute prior to arriving at #TOD, the system issues   the   VNAV   WPT   ALERT   message   and   the discrete  waypoint  light  will  flash  for  10 seconds, then be steady. (d)   Pre-Selected  Altitude  Intercept  Point (#PRESL).    When  the  system  has  an  input  from  an altitude  pre-selector  and  the  aircraft  is  flying  toward this  altitude,  a  profile  waypoint  (#PRESL)  appears  on the  VNAV  page.    #PRESL,  however,  never  becomes the vertical TO waypoint.  When the pre-selector input is valid, ETE and RANGE to #PRESL can be found on the VNAV Data page. (e)   Descent Reference Waypoints.   Descent   reference   waypoints   have   a   fixed   altitude crossing.  To create a descent reference waypoint, the pilot  can  program  a  flight  path  angle  or  a  cross  at altitude constraint. If   a   programmed   FPA   violates   a   prior   vertical constraint, the system reassigns the descent reference waypoint,  using  the  default  FPA  from  the  VNAV  Data page. v.   Remote Tuning. (1)   Tuning   Communications   Radios.       This procedure   enables   the   pilot   to   keyboard   tune   the aircraft radios via the CDU. 1.   TUNE key – Press.  The Comm Radio Tune page will be displayed. 2.   Line select key  – Press (if necessary) to   position   cursor   over   appropriate PRESET field. 3.   Frequency – Insert. NOTE Trailing zeroes are not required. 4.   ENTER  key   –  Press.    TRANSFER? will automatically appear. 5.   ENTER  key    –   Press.      The   entered PRESET frequency transfers to ACTIVE     and     displays     for     a     few seconds   before   it   goes   to   dashes.   The  new  frequency  also  displays  as the ACTIVE frequency on the appropriate comm control unit. NOTE (MAN)  adjacent  to  active  comm  frequency indicates    that    the    frequency    has    been entered  using  the  comm  control  unit.    No prompts  are  displayed  when  active  comm frequency has been keyboard entered. The  PRESET  frequency  displayed  on  the control head is not necessarily the PRESET  frequency  displayed  on  the  CDU.   Each may be entered independently. Depending   on   the   system   configuration, the   cursor   can   appear   over  the  PRESET field for either COMM 1 or COMM 2. (2)   Tuning NAV Radios By Keyboard Method If Station Identifier Is Used. 1.   TUNE  key   –   Press   until   Navigation Tune page is displayed. 2.   Line  select  key    –   Press   to   position cursor    opposite    the    desired    radio (NAV 1 or NAV 2). 3.   Station   identifier   –    Insert    or    verify entry. 4.   ENTER    key    –    Press.        The    new frequency    is    displayed    immediately and is annunciated with (KEY) adjacent  to  the  frequency  field.    If  the identifier is not found immediately, the IDENT  field  will  go  to  dashes  until the station   is   located   in   the   database.   Once   located,   the   identifier   will   be displayed and the (KEY) annunciation will shift to the identifier line. NOTE When  the  CDU  keyboard  is  used  to  tune  a navaid, the database will pair the frequency and identifier to the nearest usable navaid.   Therefore, the identifier entered may not be the same as the identifier that is displayed.   If the navaid is out of range, or a frequency conflict exists, dashes will be displayed in the IDENT field and the new frequency  will be displayed. 5.   Frequency  –  Verify  that  the  ACTIVE frequency   on   the   control   head   and CDU displays agree.