TM 1-1510-224-10 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  then  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 is 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. (11)ILS approach mode.    The  ILS  approach mode   provides   for   automatic   intercept,   capture,   and tracking   of   the   front   course   localizer   and   glideslope signals.  This allows flying a fully coupled ILS approach. Set-up for the ILS approach mode is as follows: 1. VHF navigation receiver control panel - Set desired localizer frequency. 2. V/L pushbutton selector switch (display controller)  - Depress to select LOC1 or LOC2. 3. Course pointer (EHS I) - Set inbound course on heading dial. 3-54