TM 1-1510-218-10 3B-13 (4)   Double    Needle    Pointer.      Indicates   #2 ADF or #2 VOR bearing as selected by double needle switch. (5)   Single Needle Pointer.  Indicates #1 ADF or  VOR/TACAN  bearing  as  selected  by  single  needle switch. (6)   Double  Needle  Switch.    Selects  desired signal to be displayed on double needle pointer. (a)   ADF    Position.        Selects    #2    ADF bearing information. (b)   VOR    Position.        Selects    #2    VOR bearing information. (7)   Single Needle Switch. (a)   ADF    Position.        Selects    #1    ADF bearing information. (b)   VOR Position. Selects #1 VOR/waypoint bearing information. 3B-13.  PILOT'S HORIZONTAL SITUATION INDICATOR. a.     Description.  The pilot's Horizontal Situation Indicator (HSI) combines numerous displays to provide a presentation of the aircraft position.  Refer to Figure 3B-6.      The   indicator   displays   aircraft   displacement relative   to   VOR,   localizer,   glideslope   beam,   GPS, TACAN,    and    selected    heading,    with    respect    to magnetic  north.    Any  warning  flag  in  view  indicates that  portion  of  the  HSI  display  is  unreliable.    Display brightness   is   controlled   by   a   dimming   knob  that  is concentric with the   DH SET  knob  and  located  on  the pilot's ADI. b.    Associated Controls/Indicators and Function.  Refer to Figure 2-9 Sheet 1. (1)   COURSE   Knob.      Positions   the   course pointer. (2)   HEADING  Knob.    Positions  the  heading bug to a pre-selected heading. c.     Controls/Indicators and Function. (1)   Distance Display (DIST).  Provides digital displays  of  DME/TACAN,  waypoint  or  GPS  distance.   DME/TACAN  and  waypoint  distance  is  displayed  in 1/10-mile  increments.    GPS  distance  is  displayed  in whole mile increments.  The  display  will  show  dashes when the distance input data is invalid or absent. (2)   Rotating Heading (Azimuth) Dial.   Displays gyro stabilized magnetic compass information on a dial that rotates with the aircraft throughout 360°.   The azimuth ring is graduated in 5° increments. (3)   Lubber    Line.        Fixed    heading    marks located at the fore (upper) and aft (lower) position. (4)   Heading    Bug.        The    notched    orange heading  bug  is  positioned  on  the  rotating  heading  dial by    the    heading    knob,    to    select    and    display    a preselected   compass    heading.        Once    set    to    the desired    heading,    the    heading    bug    maintains    its position  on  the  heading  dial.    The  difference  between the  bug  and  the  fore  (upper)  lubber  line  index  is  the amount  of  heading  select  error  applied  to  the  flight director  computer.    In  the  heading  mode  the  ADI  will display   the   proper   bank   commands   to   turn   to   and maintain this selected heading. (5)   COURSE   Display.      Provides   a   digital readout of selected magnetic course. (6)   Course    Pointer.        The    yellow    course pointer is positioned on the heading dial by the remote course knob, to a magnetic bearing that coincides with the selected course being flown.  The course pointer is also   positioned   by   the   RNAV   or   VLF   modes   of operation.  The course pointer rotates with the heading dial to provide a continuous readout of course error to the computer. (7)   Bearing  Pointer.    Indicates  ADF  or  NAV relative   bearing   as   selected   by   the   bearing   pointer source switch. (8)   ADF    Annunciator.        When    illuminated, indicates ADF bearing information is being displayed. (9)   Bearing   Pointer   Source   Switch.      The bearing  pointer  source  switch,  located  on  the  pilot's HSI,   provides   for   selecting   between   ADF   and   NAV bearing    information    as    presented    by    the    bearing pointer.      Each   push   of   the   select   switch   alternates selection of ADF or NAV.  Upon power-up or following long-term power interruption, NAV is displayed. (10)   NAV   Annunciator.        When    illuminated, indicates NAV bearing information is being displayed.