TM 1-1510-218-10 3-2 b.    Microphone  Jacks.     The  pilot  and  copilot are each provided a microphone jack, placarded  MIC, located   on   the   extreme   left   and   right   sides   of   the instrument  panel,  Figure  2-17,  for  use  with  the  hand held  microphone  or  headset  microphone.    There  is  a microphone   jack   for   the   oxygen   mask   microphone, located next to the oxygen outlets. (1)   MIC HEADSET Jack .  This jack provides a means of connecting microphone headset assembly to audio system. (2)   MIC Jack .  This jack provides a means of connecting  hand–held  microphone  with  push–to–talk capability to the audio system. c.     Microphone Jack Selector  Switches.   The pilot   and   copilot   are   each   provided   with   a   switch, placarded  MIC  HEADSET  /  OXYGEN  MASK, located on  the  extreme  left  and  right  sides  of  the  instrument panel. (1)   MIC HEADSET / OXYGEN MASK Switch.    Selects  which  microphone  will  be  connected to audio system. (2)   MIC HEADSET.  Utilizes either hand-held microphone   or   headset–microphone   assembly   with audio system. (3)   OXYGEN MASK.  Utilizes microphone in oxygen mask assembly with audio system. d.    External   Headset-Microphone   Jack.      A jack  on  the  nose  gear  strut,  placarded  MIC JACK, is available   for   use   by   ground   personnel.      The   jack connects headphones and microphone to the aircraft's interphone system. e.     Cockpit Floor Foot Microphone Switch.  A floor–mounted  foot  microphone  switch  is  installed  on the  floor  on  the  copilot's side.  The switch allows the copilot  to  key  the  system  selected  by  the  transmitter selector    switch    on    the    audio    control    panel    while performing other operations. Section III.  NAVIGATION 3-6.  NAVIGATION 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.      The common  avionics  in  the  navigation  equipment  group consists of the gyromagnetic compass systems. 3-7.  GLOBAL POSITIONING SYSTEM (KLN 90B). a.     Description. The Global Positioning System   (GPS)   is   a   satellite-based   radio   navigation system that utilizes precise range measurements from GPS satellites to determine precise position anywhere in    the    world.        The    KLN    90B    provides    en    route navigation     information     and     non-precision     (except localizer, LDA, and SDF) instrument approach navigation. b.    Components.  (1)   KLN   90B   Panel.        Located    above    the weather  radar  on  the  instrument  panel  are  the  GPS sensor, the navigational computer, a CRT display, and all controls required to operate the unit, Figure 3-1.  It also houses the database cartridge that plugs directly into the back of the unit.  Refer to Figure 3–1. (2)   External Annunciators/Switches.  A panel located  just  to  the  right  of  the  fire  handles    D2  T  or above   the   KLN   90B   control   panel   C      D1   on   the instrument  panel  contains  switches  to  select   OBS  or LEG  during  en  route  navigation  and  a  switch  to  arm the unit during approach.  It also has annunciators to indicate  when  a  message  is  active,  when  waypoint sequencing    is    about    to    occur,    and    when    altitude alerting   is   occurring.      The   annunciator   panel   also contains  a  jack  to  load  the  database  from  a  laptop computer.  Refer to Figure 3-2. (3)   Antenna.    A  GPS  antenna  is  located  on the top of the fuselage at approximately STA 220. c.     Power.    Vdc  to  the  KLN  90B  is  provided through a dc circuit breaker panel through a 5-ampere circuit breaker labeled  KLN 90B C  D or FMS #2  T1  .