TM 1-1510-218-10 3B-21 1.     Selected Altitude Display 2.     Altitude Selector SET Knob Figure 3B-11.  Altitude Select Controller 3B-20.  GYROMAGNETIC COMPASS SYSTEM. a.     Description. Two identical compass systems   provide   accurate  directional  information  for the  aircraft  at  all  latitudes  of  the  earth.    For  heading reference, two modes of operation are used: directional   gyro   (FREE)   mode,   or   slaved   (SLAVE) mode.        In    areas    where    magnetic    references    are reliable,  the  system  is  operated  in  the  SLAVE  mode.   In   this   mode,   the   directional   gyro   is   slaved   to   the magnetic  flux  valve  that  supplies  magnetic  reference for   correction   of   the   apparent   drift   of   the   gyro.      In FREE mode, the system is operated as a free gyro.  In this mode, latitude corrections are manually introduced using the  INCREASE  /  DECREASE  switches,  Figure 17,   Sheet   2.      The   slave/free   mode   is   selected,   as desired, using the SLAVE / FREE switch, Figure 2-17, Sheet 2. b.    Controls and Functions.  (1)   COMPASS #1   Switch.    Selects  desired source of magnetic heading information for pilot's flight director/autopilot, HSI, flight management system and copilot's RMI.  Refer to Figure 2-17, Sheet 2. (2)   COMPASS # 2   Switch.    Selects  desired source  of  magnetic  heading  information  for  copilot's flight director/ autopilot, HSI, and pilot's RMI. (3)   ALL    SYSTEMS    ON    COMPASS    1    / NORM  /  ALL  SYSTEMS  ON  COMPASS  2  Switch. This  switch,  located  adjacent  to  the  pilot's  compass switch, allows the pilot to select all systems to operate off  compass  1  or  compass  2.    When  the  switch  is  in the  NORM  position,  magnetic  heading  information  is provided   to   the   pilot's   flight   director/autopilot,   HSI, flight management system, and copilot's RMI. (4)   GYRO SLAVE / FREE Switch.  Controls system mode of operation. (a)   SLAVE.      Places   system   in   SLAVE mode. (b)   FREE.        Places    system    in    FREE mode. (5)   INCREASE / DECREASE Switch. Provides manual fast synchronization for the system. (a)   INCREASE.    Causes  gyro  heading output to increase. (b)   DECREASE.    Causes  gyro  heading output to decrease. (6)   Compass    Synchronization    Annunciator. Two compass slave annunciators, located on both the pilot's and copilot's HSI's, provide a visual indication of system synchronization. 3B-21.  NAV RECEIVERS (KFS-579A, KNR-634). a.     Description. Two NAV (KFS-579A/ KNR-634 and KFS-564A/KNR-634) airborne navigation receivers are provided which allow selection and storing of navigation frequencies.  Refer to Figures 3B-12 and Figure 3B -13. The  NAV  receivers  receive  and  interpret  VHF omnidirectional radio range (VOR) and localizer (LOC) signals  in  the  frequency  range  of  108.00  to  117.95 MHz,  glideslope  signals  in  the  frequency  range  of 329.15 to 335.00 MHz, and marker beacon signals to 75 MHz. In  addition,  the  KFS-579A  #1  NAV/TAC  control tunes    the    KTU-709    DME/TACAN    system    to    252 TACAN   channels.      Fifty-two   TACAN   channels   are paired with frequencies in the COMM band.  These are channels   1   through   16,   and   60   through   69,   which correspond  to  VHF  frequencies  134.40  MHz  through 135.95 MHz respectively. Marker   beacon   receivers   are   utilized   with   the NAV receivers, to provide accurate fixes informing the pilot of his passage over beacon stations.  Three types of   beacons   are   used.      They   are   the   outer   (blue annunciator)    marker,    middle    (amber    annunciator) marker,  and  inner  (white  annunciator)  marker.    The three   markers   are   used   in   conjunction   with   radio instrument   landing   systems.      The   markers   are   all transmitted   at   a   frequency   of   75   MHz   using   three different frequencies of AM modulation.