TM 1-1510-218-10 2-15 2-8.  LANDING GEAR SYSTEM D2 T . The retractable tricycle landing gear is electrically  controlled  and  hydraulically  actuated.   The landing  gear  assemblies  are  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, gear up pressure switch  and  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 a yellow caution light, placarded HYD FLUID LOW, on the annunciator panel, whenever the fluid level in the power   pack   is   low.      The   annunciator   is   tested  by pressing   the    HYD   FLUID   SENSOR   TEST   switch located on pilot's subpanel.  Refer to Figure 2-8. Power  for  the  power  pack  is  supplied  from  the No.  5  dual  fed  buss,  through  a  landing  gear  motor relay  and  a  60-ampere  circuit  breaker  located  under the  floor  board  forward  of  the  main  spar.    The motor relay   is   energized   by   power   furnished   through   a 2-ampere  LANDING GEAR CONTROL circuit breaker located on the overhead circuit breaker panel, and the downlock    switches.         The    power    pack    motor    is protected   by   a   time   delay   module,   which   senses operation  voltage  through  a  5-ampere  circuit  breaker.   Both  are  located  beneath  the  aisle  way  floorboards forward of the main spar.   Landing gear extension or retraction is normally accomplished in 5 to 6 seconds.   Voltage to the  power pack is terminated after the fully extended or retracted position is reached (approximately  23  seconds).    If  electrical  power  has not terminated after the normal extension or retraction time  lapse,  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  that  lock  in  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.    However,  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  pressure  is  controlled  by  the  power  pack pressure   switch   and   an   accumulator   that   is   pre- charged with nitrogen to 800 ± 50 psi.  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  gear  is  retracted.    Air-oil  type  shock  struts, filled   with   compressed   air   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 on the left subpanel.   The control switch and associated relay circuits are protected by a 2-ampere circuit breaker, placarded  LANDING GEAR CONTROL,  located  on  the  overhead  circuit  breaker panel. b.  Landing    Gear    Down    Position-Indicator Lights.    Landing  gear  down  position  is  indicated  by three   green   lights   on   the   left   subpanel,   placarded GEAR DOWN D2  T1 .  Refer to Figure 2-8, Sheets 1 and 2.  Visual indication of the landing gear position is provided  by  individual  green   GEAR  DOWN indicator lights, placarded   NOSE  L  /  R,  on  the  left  subpanel.  T2  .  Refer  to  Figure  2-8,  Sheet  3.     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 overhead circuit breaker panel. c.   Landing   Gear   Position   Warning   Lights.    Two  red  parallel-wired  indicator  lights  located  in  the LDG GEAR CONTROL  D2 T1 or LDG GEAR CONTR T2 switch handle illuminate to show that the gear is in transit or unlocked.   The  red  lights  in  the  handle  also illuminate   when   the   landing   gear   warning   horn   is actuated.    Both  red  lights  indicate  the  same  warning conditions,    but    two    are    provided    for    a    fail-safe indication in the event one bulb burns out.   The circuit is  protected  by  a  5-ampere circuit breaker, placarded LANDING GEAR IND, on the overhead circuit breaker panel. d.  Landing  Gear  Warning  Light  Test  Switch.   A test switch, placarded  HDL  LT  TEST, is located on the left subpanel.  Failure of the landing gear handle to illuminate    red    when    this    test    switch    is    pressed indicates  two  defective  bulbs  or  a  circuit  fault.    The circuit   is   protected   by   a   5-ampere   circuit   breaker, placarded  LANDING GEAR WARN, on the overhead circuit breaker panel.