TM 1-1510-224-10 4. Heading    marker    (EHSI)        -    Set desired intercept heading for course interception. The EHSI will now display the relative position of the  aircraft  to  the  center  of  the  localizer  beam  and  the desired inbound course.  With the heading marker set for intercept,   the   heading   select   mode   can   be   used   to perform the intercept.  Outside the normal capture range of the localizer signal (between one and two dots on the EHSI),  depressing  the  APR  pushbutton  switch  on  the flight   director   mode   selector   will   cause   the   EADI   to annunciate LOC in white and HDG in green.  The aircraft will  now  be  flying  the  desired  heading  intercept  and  the system   will   be   armed   for   automatic   localizer   beam capture. With    the    aircraft    approaching    the    selected course  interception,  the  lateral  beam  sensor  (LBS)    is monitoring localizer beam deviation, beam rate, and true airspeed.    At  the  computed  time,  the  LBS  will  trip  and capture  the  localizer  signal.    The  flight  control  computer will   drop   the   heading   select   mode   and   generate   the proper   roll   command   to   bank   the   aircraft   toward   the localizer beam center.  When the LBS trips, the EADI will display  LOC  in  green.    LOC  will  be  enclosed  in  a  white box for 5 seconds. The glideslope  portion  of  the  approach  mode  is used for the automatic intercept, capture, and tracking of the  glideslope  beam.    The  beam  is  used  to  guide  the aircraft  down  to  the  runway  in  a  linear  descent.    Typical glideslope  beam  angles  vary  between  2  and  3  degrees, depending   on   terrain.      When   the   glideslope   mode   is used as the vertical portion of the approach, it allows the pilot  to  fly  a  fully  coupled  ILS  approach.    The  mode  is interlocked,  so  that  glideslope  capture  is  inhibited  until localizer capture has occurred. As the aircraft approaches the glideslope beam, the vertical beam sensor monitors true airspeed, vertical speed, and glideslope deviation to determine the correct capture point.  At glideslope capture, the computer drops any     other     vertical     mode     that     was     in     use,     and automatically  generates  a  pitch  command  to  smoothly track    the    glideslope    beam.        Gain    programming    is performed  on  the  glideslope  signal  to  compensate  for the   aircraft   closing   on   the   glideslope   transmitter   and beam  convergence  caused  by  the  directional  properties of  the  glideslope  antenna.    Glideslope  programming  is normally accomplished as a function of radio altitude and vertical    speed.        If    the    radio    altimeter    is    not    valid, glideslope    gain    programming    is    accomplished    as   a function   of   preset   height-   above-the-runway   estimates and run-down as a function of true airspeed. The ILS approach mode is cancelled by: Depressing   NAV   or   APR   pushbutton   switch- indicator on the flight director mode selector. Selecting a VOR frequency on the selected VHF navigation receiver control panel. Selecting go-around mode. Selecting standby mode. Selecting back course mode. Coupling   flight   control   computer   to   the   cross- side EFIS. Selecting    an    alternate    ATT,    HDG,    or    NAV source on the display controller. When   the   aircraft   satisfies   the   localizer   track conditions,  the  course  error  signal  is  removed  from  the lateral  steering  command.    This  leaves  radio  deviation, roll attitude, and lateral acceleration to track the localizer signal, and to compensate for localizer beam standoff in the    presence    of    a    crosswind.        The    system    will automatically  compensate  for  a  crosswind  of  up  to  45 degrees course error. (12)Pitch   attitude   hold   mode.      The   pitch attitude   hold   mode   is   the   basic   vertical   flight   director mode.    It  is  activated  when  a  flight  director  lateral  (roll) mode   is   selected   without   an   accompanying   vertical (pitch)  mode.    There  is  no  annunciation  for  pitch  hold mode   although   the   basic    AP   ENG    annunciation    is available.  The pitch command on the EADI provides the pilot  with  a  pitch  reference  corresponding  to  the  pitch attitude  existing  at  the  moment  the  lateral  mode  was selected.    This  pitch  reference  can  be  changed  with  the touch   control   steering   (TCS )   switch   located   on   the control wheels.  The reference pitch attitude can also be changed as a function of the pitch wheel on the autopilot controller  when  the  autopilot  is  engaged.    Pitch  attitude hold  mode  may  be  cancelled  by  selecting  any  vertical mode or the automatic capture of a vertical mode. (13)Vertical speed  hold  mode.    The  vertical speed  hold  mode  is  used  to  automatically  maintain  the aircraft at a selected vertical speed reference.  To initiate the   mode,   the   aircraft   is   maneuvered   to   the   desired climb  or  descent  attitude  to  establish  the  vertical  speed reference,  then  the  mode  is  engaged  by  depressing  the VS   pushbutton   switch-indicator   on   the   flight   director mode   selector.      The   reference   vertical   speed   can   be changed  by  pushing  the  touch  control  steering  (TCS) switch on the control wheel and maneuvering the aircraft to a new vertical speed reference and then releasing the switch.        The    vertical    speed    reference    can    also    be changed  by  the  use  of  the  pitch  wheel  on  the  autopilot controller. When  the  vertical  speed  mode  is  engaged,   VS (green) will be annunciated on the EADI, and the vertical speed  target  will  be  displayed  in  the  lower  left  corner  of the EADI.  When the vertical speed reference is changed by  using  the  pitch  wheel  on  the  autopilot  controller,  the EADI's    will    indicate    the    commanded    vertical    speed reference.  Actual aircraft vertical speed will be displayed on  the  vertical  speed  indicator.    Selecting  vertical  speed (VS) will reset all previously selected vertical modes. 3-55