TM 1-1510-225-10 2-10 2-6.  EXHAUST AND PROPELLER DANGER AREAS. Exhaust    and    propeller    danger    areas    to    be avoided by personnel while aircraft engines are being operated  on  the  ground  are  depicted  in  Figure  2-4.   Distance  to  be  maintained  with  engines  operating  at idle   are   also   shown.      Temperature   and   velocity   of exhaust  gases  at  varying  locations  aft  of  the  exhaust stacks  are  shown  for  maximum  power.    The  danger area extends to 40 feet aft of the exhaust stack outlets.   Distances  to  be  maintained  with  engines  operating  at idle and propeller danger areas are also shown. 2-7.  LANDING GEAR SYSTEM. The retractable tricycle landing gear is electrically  controlled  and  hydraulically  actuated.    The landing  gear  is  extended  and  retracted  by  a  hydraulic power   pack,   located  in  the  left  wing  center  section, forward  of  the  main  spar.    The  power  pack  consists primarily of a hydraulic pump, a 28 Vdc motor, a gear selector    valve    and    solenoid,    a    two    section    fluid reservoir,   filter   screens,   a   gear-up  pressure  switch, and   a   low   fluid   level   sensor.      Engine   bleed   air, regulated  to  18  to  20  psi,  is  plumbed  into  the  power pack  reservoir  and  the  system  fill  reservoir  to  prevent cavitation of the pump.  The fluid level sensor activates an yellow caution annunciator, placarded  HYD FLUID LOW,  located  on  the  caution  /  advisory  annunciator panel,  whenever  the  fluid  level  in  the  power  pack  is low.  Test the annunciator by pressing the  HYD FLUID SENSOR TEST switch located on the pilot's subpanel for the aircraft.  Refer to Figure 2-5, Sheets 1  through 8. Power  for  the  hydraulic  power  pack  is  supplied through the landing gear motor relay and a 60-ampere circuit  breaker  located  under  the  floorboard  forward  of the main spar.  The motor relay is energized by power furnished    through    the   2-ampere   LANDING   GEAR RELAY circuit breaker located on the pilot's subpanel.   A  time  delay  module  that  senses  operation  voltage through a 5-ampere circuit breaker protects the power pack  motor.    Both  are  located  beneath  the  aisleway floorboards,  forward  of  the  main  spar.    Landing  gear extension  or  retraction  is  normally  accomplished  in  6 to 7 seconds.  Voltage to the power pack is terminated after    the    fully    extended    or    retracted    position    is reached.  If electrical power has not terminated within 14 seconds, a relay and  2-ampere landing gear circuit breaker  will  open  and  electrical  power  to  the  system power pack will be interrupted. The landing gear system utilizes folding braces, called drag legs, which lock into place when the gear is   fully   extended.      The   nose   landing   gear  actuator incorporates an internal down lock to hold the gear in the   fully   extended   position.      The   two   main   landing gears    are    held    in    the    fully    extended    position    by mechanical  hook  and  pin  locks.    The  landing  gear  is held  in  the  up  position  by  hydraulic  pressure.    The power  pack  pressure  switch  and  an  accumulator  that is pre-charged with nitrogen to 800 ± 50 psi control the pressure.  Gear doors are opened and closed through a  mechanical  linkage  connected  to  the  landing  gear.   The  nose  wheel  steering  mechanism  is  automatically centered and the rudder pedals relieved of the steering load when the landing gears are retracted.  Air-oil type shock   struts,   filled   with   compressed   nitrogen   and hydraulic fluid, are incorporated with the landing gear. a.   Landing   Gear   Control   Switch.      Landing gear   system   operation   is   controlled   by   a   manually actuated, wheel-shaped switch, placarded  LDG GEAR CONTROL  UP  /  DN,  located  on  the  pilot's  subpanel.   The  control  switch  and  associated  relay  circuits  are protected   by   a  2 -ampere   circuit  breaker,  placarded LANDING    GEAR    RELAY,    located    on    the    pilot's subpanel. b.  Landing    Gear    Down    Position    Indicator Lights.     Visual  indication  of  landing  gear  position  is provided   by   three   individual   green    GEAR    DOWN position indicator lights located on the pilot's subpanel.   Testing   of   the   indicator   lights   is   accomplished   by pressing  the  annunciator  test  switch.    The  circuit  is protected   by   a  5 -ampere  circuit  breaker,  placarded LANDING   GEAR   IND,   on   the   right   sidewall   circuit breaker  panel.    Refer  to  Figure 2-6, Sheets 1 through 5, for the circuit breaker panels for the C-12R, C-12T3, and C-12F3 (OSA) (ANG) aircraft. c.   Landing   Gear   Position   Warning   Lights.   Two  parallel-wired  red  indicator  lights,  located  in  the LDG   GEAR   CONTROL  switch  handle,  illuminate  to show that the gear is in transit or unlocked.  The red indicator lights in the handle also illuminate when the landing   gear   warning   horn   is   actuated.      Both   red indicator  lights  indicate  the  same  warning  conditions, but  two  are  provided  for  a  fail-safe  indication in case one   bulb   bums   out.      The   circuit   is   protected   by   a 5-ampere circuit breaker, placarded  LANDING GEAR IND, on the right sidewall circuit breaker panel. d.  Landing Gear Warning Indicator Light Test Switch.    A  test  switch,  placarded   HDL  LT  TEST, is located on the pilot's subpanel.  When this test switch is   pressed,   failure   of   the   landing   gear   handle   to illuminate red indicates two defective bulbs or a circuit fault.    The  circuit  is  protected  by  a  5-ampere  circuit breaker, placarded   LANDING  GEAR  WARN,  on   the right sidewall circuit breaker panel.