TM 1-1510-218-10 3A-16 NOTE Nominal   tune   time   of   the   pa-coupler   is approximately 5 seconds; therefore, the RF TEST lamp indications below are only valid for   approximately   5   seconds   after   initial keying. 5.   If the RF TEST lamp stays illuminated continuously,   the   receiver-exciter   is faulty.  If the  RF TEST lamp blinks on and off, the pa-coupler is faulty. 6.   Tune    Cycle    Complete.        If    the    RF TEST lamp is not illuminated, the tune tone   drops,   and   a   beeping   tone   is heard  at  the  end  of  the  time,  the  pa- coupler  and  coupler  mount  failed  to tune the antenna. 7.   If  RF  TEST  lamp  is  not  illuminated, switch  to  the  USB  mode  and  supply audio  input  while  holding  the  system keyed.      If   sidetone   is   not   audible, check audio interphone or microphone system  before  replacing  the  eceiver- exciter.        Presence    of    a    sidetone indicates  that  the  system  is  working properly. 3A-12.  EMERGENCY LOCATOR TRANSMITTER (ELT). a.   Description. An Emergency Locator Transmitter  (ELT)  is  provided  to  assist  in  locating  an aircraft and crew in the event an emergency landing is necessitated.      The   output   frequency   is   121.5   and 243 MHz   simultaneously.      Range   is   approximately line-of-sight.  The aircraft may be equipped with one of three  different  ELT’s:  the  TR70-13,  the  TR70-17,  or the ELT-10.  All three have a RESET  switch and  ON / OFF  /  ARM  switch  located  on  the  transmitter.    The TR70-13   and   ELT-10   are   equipped   with   a   switch, accessible through an access opening in the right side of the aft fuselage.  In the event the impact switch has been inadvertently actuated, the  beacon  can  be  reset by  actuating  the  remote  mounted  switch  to  the   RE ARM (aft) position (TR70-13) or by firmly pressing the RESET  switch on the front of the case.  Access to the ELT is through the door on the bottom of the aft right fuselage. b.  Controls and Functions.  (1)   TR70-17. (a)  ON  /  OFF  /  ARM   Switch.    Controls operation of the set. 1   ON.          Turns     set     on     for     test purposes. 2   OFF.  Turns set off. 3   ARM .  Arms set so that it will turn on automatically in an impact. NOTE The TR70-17 has no remote switch. (2)   TR70-13, Remote Switch. (a)  RE   ARM   /   ARM   /   XMIT   Switch.   Resets, arms, or activates transmitter. 1   RE  ARM.    Resets  transmitter  if  it has been activated. 2   ARM.  Arms transmitter to activate automatically on impact.   Switch on front of transmitter must be set to ARM. 3   XMIT.  Activates transmitter for test purposes.  Switch on front of transmitter may be set to OFF or  ARM. (3)   ELT-10, Remote Switch. (a)  ARM    /    XMIT    Switch.        Arms    or activates transmitter. 1   ARM.        Arms    transmitter    when switch on front of transmitter is set to ARM. 2   XMIT.  Activates transmitter for test purposes. Section III.  NAVIGATION 3A-13.  DESCRIPTION. The overall navigation equipment group provides the  pilot  and  copilot  with  the  instrumentation  required to establish and maintain an accurate flight course and position   and   to   make   an   approach   on  instruments under    Instrument    Meteorological    Conditions    (IMC).   The  navigation  configuration  includes  equipment  for determining  attitude,  position,  destination  range  and bearing, heading reference and groundspeed.