TM 1-1510-224-10 mode, perform the following: 1. VOR navigation receiver control panel - Set desired VOR frequency. 2. V/L pushbutton selector switch (display   controller)      -   Depress   to select VOR1 or VOR2. 3. Course pointer (EHSI)  - Set desired course on heading dial. 4. Heading     marker     (EHSI)          -     Set desired intercept heading for selected course. With   the   aircraft   outside   the   normal   capture range   of   the   VOR   signal   (typically,   course   deviation indicator   on   EHSI   off   course   by   more   than   2   dots), engage the   NAV  switch-indicator  on  the  flight  director mode    selector.        HDG    switch-indicator    on    the    flight director mode selector panel will illuminate   ON,  and  the NAV    switch-indicator    will    annunciate    ARM.        HDG (green) and  VOR ARM  (white)  will  also  be  annunciated on  the  EADI.    The  flight  control  computer  is  now  armed to   capture   the   VOR   signal,   and   is   generating   a   roll command to fly the heading select mode. When   reaching   the   lateral   beam   sensor   trip point,   the   system   will   automatically   drop   the   heading select  mode  and  will  switch  to  the  VOR  capture  phase. The EADI will display the following indications: VOR annunciator (white) will extinguish. HDG annunciator (green) will extinguish. NAV   (green)   will   be   annunciated   and   will   be enclosed  in  a  white  box  for  5  seconds  to  indicate  the capture phase. The  heading  pushbutton  switch-indicator  on  the autopilot/flight  director  mode  selector  will  extinguish  and the   NAV   pushbutton   switch-indicator   will   switch   from ARM to  CAP. The   flight   control   computer   will   generate   the proper  roll  command  to  capture  and  track  the  selected VOR radial. Course  select  error  signal  is  established  by  the heading   selected   by   the   course   pointer   on   the   EHSI. This signal represents the difference between the actual aircraft   heading   and   the   desired   course.      The   course error signal is then sent from the symbol generator to the flight control computer. The   radio   deviation   signal   is   routed   from   the navigation  receiver  to  the  symbol  generator  and  flight control computer.  The signal is lateral gain programmed in the flight control computer. The  lateral  gain  programming  is  performed  as  a function of DME distance to the station (if available), true airspeed, and barometric altitude. This gain programming   adjusts   for   the   aircraft   going   toward   or away from the VOR station. NOTE If  possible,  avoid  using  DME  hold  or  having N/A    as    a    distance    display    annunciation during  VOR  capture  and  tracking.    When  in this   condition   the   flight   control   computer cannot use DME distance for gain programming. When    flying    a    VOR    intercept,    the    optimum intercept   angle   is   less   than   45   degrees.      When   the aircraft  satisfies  VOR  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 VOR signal, and to compensate for  beam  standoff  in  the  presence  of  a  crosswind.    The system will automatically compensate for a crosswind of up to 45 degrees course error. As  the  aircraft  approaches  the  VOR  station,  it will   enter   a   zone   of   unstable   radio   signals   (zone   of confusion).    This  zone  radiates  upward  from  the  station in the shape of a truncated cone.  In this area, the radio signal   becomes   highly   erratic   and   it   is   desirable   to remove   it   from   the   roll   command.      The   overstation sensor   monitors   entry   into   the   zone   of   confusion   and removes radio deviation from the roll command. The system also uses the collocated DME signal (if available)  to adjust tracking gains. When   over   the   VOR   station,   the   system   will accept and follow a course change of up to 30 degrees. (5)      VOR   approach   mode.        The    set-up procedure  for  the  VOR  approach  mode  is  the  same  as for    VOR    tracking,    except    the    VORAPR    pushbutton switch-indicator on the mode selector panel is depressed instead    of    the    NAV    switch-indicator.        ARM    will    be annunciated   by   the   VORAPP   switch-indicator   on   the mode selector panel and  APR  will be displayed in white on the EADL The  flight  control  computer  will  now  apply  the gains appropriate for a VOR approach.  Upon capture of the selected course, the VOR APP mode selector switch will    annunciate    capture    (CAP),    and     APR     will     be annunciated on the EADI in green. (6)    TACAN  navigation  and  approach  mode. TACAN navigation and approaches are accomplished in a  similar  manner  to  VOR  navigation  and  approaches. Prior to engaging the mode, perform the following: 1. TACAN   navigation   receiver   control panel - Set desired channel. 2. INS/TCN pushbutton selector switch (display    controller)    -    Depress    to select TCN. 3. Course  pointer  (EHSI)  -  Set  desired course on heading dial. 3-52