TM 1-1510-225-10 3C-36 1.  TACAN Channel Display 2.  VOL On/Off Knob 3.  X/Y Switch 4.  Channel Selector/Volume Control 5.  TEST Push Button Figure 3C-16.  TACAN Control Panel 1.  Distance To Station N.M. (Slant Range) 2.  Groundspeed (KTS) 3.  Time To Station (Minutes) Figure 3C-17.  TACAN Indicator NOTE THE  TACAN  portion  of  a  VORTAC  station will   be   read   on   the   HSI   only   when   the proper  channel  is  selected  on  the  TACAN control  panel  and  TACAN  is  selected  with the     HSI     selector     switch.          With     VOR selected, the VIR-32 receivers are tuned to the  VOR  portion  and  the  DME-42 receives the DME portion. The   TACAN   system   may   be   operated   on   the flight  director  system  or  connected  to  and  used  with the  autopilot  system.    When  employed  as  the  primary means  of  navigation,  aircraft  flight  may  be  controlled manually   or   by   the   autopilot   magnetic   bearing   to TACAN stations may be shown on the RMI's when the VOR  ADF  /  TACAN  ADF  push  buttons,  to  the  lower left of the pilots' RMI and to the far right of the copilot's instrument   panel,   are   pressed   to   the   TACAN   ADF position.  Also, the  VOR  ADF  push  button  for  the  #1 (yellow)  needle  on  the  RMI’s  must  be  pressed  to  the VOR  position.    Course  deviation  only  may  be  shown on the HSI’s when the  TACAN selector for the HSI is pressed.  TACAN slant range is displayed on each HSI range in the digital distance display.  TACAN distance, groundspeed, and time-to-station  are  all  displayed  on the TACAN indicator located on the copilot’s instrument panel. NOTE Under  conditions  of  bright  direct  sunlight, the  VOR  ADF  /  TACAN  ADF  push  button indicate the selected channel. The  TACAN  control  panel  enables  selection  of the    TACAN    frequency    (channel)    to    be    used    and provides self-test of TACAN circuits.  X or Y channel is selected by the X / Y switch.  Y channels differ from X channels in frequency assignment and pulse spacing.   Y    channels    were    developed    to    relieve    frequency congestion.        Use    of    the    Y    channels    has    been implemented along with 0.05 MHz spacing for VOR/VORTAC  stations  and  Y  channels  are  paired with    these    new    frequencies    (for    example,    VOR frequency 113.1 is TACAN channel 78X; VOR 113.15 is TACAN channel 78Y).   DoD FLIP charts will include the  Y  designation  in  the  data  block  for  Radio  Aids  to Navigation.  The small (outer) control provides system power   ON   /   OFF   and   station   identity   tone   volume control.    TACAN  circuits  are  protected  by  a   TACAN circuit breaker on avionics portion of the copilot's right sidewall panel. b.    Controls, Indicators, and Functions.  (1)   TACAN  Control  Panel.    Refer  to  Figure 3C-16. (a)  TACAN  Channel  Display  –  Indicates selected channel. (b)  VOL On/Off Knob  – Provides system power and volume control. (c)  X / Y Switch  – Selects either  X or  Y mode. (d)  Channel  Selectors  –  Selects  desired channel. (e)  TEST  Push  Button  –  When  pressed, activates functional self-test. (2)   TACAN Indicator.  Refer to Figure 3C-17.