TM 1-1510-223-10 The   landing   gear   system   utilizes   folding   braces called  drag  legs,  that  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.      However,   the   two   main landing  gear  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  precharged  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    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  CONTR  - UP - DN, on the pilot's subpanel (fig.  2-6).  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 (fig.  2-7). b. Landing Gear Down Position Indicator Lights. Visual indication of the 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 over-head circuit breaker panel (fig.  2-7). c. Landing Gear Position Warning Lights.   Two red  parallel-wired  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 overhead circuit breaker panel (fig. 2-7). d. Landing  Gear  Warning  Indicator  Light  Test Switch.      A   test   switch,   placarded   HDL   LT   TEST,   is located in the pilot's subpanel (fig.  2-6).  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   HORN,   on   the overhead circuit breaker panel (fig.  2-7). e. Landing Gear Warning System.   The landing gear  warning  system  is  provided  to  warn  the  pilot  that the landing gear is not down and locked during specific flight regimes. Various warning modes result, depending upon the position of the flaps. At airspeeds above 140 KIAS with flaps in the UP or   APPROACH   position   and   either   or   both   POWER levers    retarded    below    approximately    84%    N₁,    the landing  gear  switch  handle  annunciator  will  illuminate. The horn is automatically silenced by an altitude sensing switch,   provided   to   silence   the   landing   gear   warning horn  when  above  12,500  feet.    This  prevents  the  horn from  sounding  above  12,500  feet  when  either  POWER lever   is   pulled   back,   provided   the   flaps   are   at   the approach position or above. At airspeeds below 140 KIAS with flaps in the UP or  APPROACH  positions  with  either  or  both  POWER levers    retarded    below    approximately    84%    N₁,    the warning   horn   will   sound   and   the   landing   gear   switch handle indicator lights will illuminate.  The horn can be silenced   by   moving   the   WARNING   HORN   SILENCE switch   located   adjacent   to   the   landing   gear   switch handle, to the up position.  However, the annunciators in the landing gear switch handle cannot be canceled.  The gear   warning   silence   switch   is   a   magnetically   held switch.  Once actuated it will stay in the up position until both   POWER   levers   are   advanced   above   86%   N₁, and/or   airspeed   increases   above   approximately   153 KIAS. In   either   case   (airspeeds   above   or   below   140 KIAS) the landing gear warning system will be rearmed if both power levers are advanced above 86% N₁. With  the  landing  gear  retracted  and  flaps  beyond the APPROACH position, the warning horn and landing gear    switch    handle    annunciators    will    be    activated regardless  of  the  power  setting.    The  horn  cannot  be silenced  in  this  case,  until  either  the  landing  gear  is lowered,    or    the    flaps    are    retracted    to    the    UP    or APPROACH position. f. Landing   Gear   Warning   Horn   Test   Switch. The  warning  horn  and  gear  handle  indicator  lights  can be tested by placing the switch placarded STALL WARN TEST  -  OFF  -  LDG  GEAR  WARN  TEST  to  the  LDG GEAR WARN TEST position (fig.  26).  The gear handle warning  lights  will  illuminate,  and  the  warning  horn  will sound.  Releasing the LDG GEAR WARN TEST switch to   the   OFF   position   will   extinguish   the   gear   handle indicator   lights,   and   silence   the   warning   horn.      The landing  gear  warning  horn  circuit  is  protected  by  a  5- ampere   circuit   breaker,   placarded   LANDING   GEAR HORN,  located  on  the  overhead  circuit  breaker  panel (fig.  2-7). g. Landing   Gear   Safety   Switches.     A   safety switch  on  each  main  landing  gear  shock  strut  controls the  operation  of  various  aircraft  systems  that  function only    during    flight    or    only    during    ground    operation. These switches are mechanically actuated whenever the main landing gear 2-14