TM 1-1510-223-10 1. VHF navigation receiver control panel - Set desired localizer frequency. 2. V/L pushbutton selector switch (display controller) - Depress to select LOC1 or LOCZ 3. Course pointer (EHSI) - Set inbound course on heading dial. 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,   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 NAV or APR pushbutton switch on the flight director mode selector will cause the EADI to annunciate LOC and GS 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    and    glideslope    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. If   both   radio   altitude   and   glideslope   deviation   are valid,   distance   is   calculated   using   radio   altitude   and glideslope  deviation  data  If  only  radio  altitude  is  valid, distance is first estimated for capture.  It is assumed that an    approach    to    the    runway    is    being    made    without glideslope,   and   distance   is   calculated   based   on   radio altitude  only.    If  radio  altitude  information  is  not  valid, distance is estimated as a function of glideslope deviation and true airspeed.  If neither radio altitude nor glideslope data  is  valid,  distance  is  estimated  as  a  function  of  true airspeed and time, The glideslope 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. (10) Back course mode.   The  back  course  mode (BC)    provides    for    automatic    intercept,    capture    and tracking of the back course localizer signal.  When flying a  back  course  localizer  approach,  glideslope  capture  is automatically inhibited.  The back course mode is set up and  flown  exactly  like  a  front  course  localizer  approach, with the following differences: Back  course  (BC)  is  selected  on  the  flight  director mode selector. With   the   aircraft   outside   the   normal   back   course localizer  capture  limits,  the  EADI  will  annunciate  BC  in white and HDG in green. At back course capture, the EADI will annunciate BC in   green   (BC   will   be   enclosed   in   a   white   box   for   5 seconds). When  the  back  course  mode  has  been  selected  on the flight director mode selector, logic in the flight control computer was established to internally reverse the polarity of   the   course   error   and   localizer   signals,   and   provide expanded   localizer   display   on   the   EADI.      Also   a   gain change  takes  place  in  the  computer  when  BC  has  been selected,   since   the   aircraft   will   now   be   closer   to   the localizer transmitter by the length of the runway plus 1000 feet.  At back course capture, the flight control computer will  generate  a  roll  command  to  capture  and  track  the back course localizer signal. The back course mode is cancelled by: Depressing the BC 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 heading mode Coupling   flight   control   computer   to   the   cross-side EFIS Selecting an alternate ATT, HDG, or NAV source on the display controller. 3-53