TM 1-1510-224-10 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,  that  lock  into  place  when  the  gear  are 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  gear  are held  in  the  fully  extended  position  by  mechanical  hook and   pin   locks.      The   landing   gear   are   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  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 CONTR  UP  DN,  on  the  pilot's  subpanel  (fig.    2-8).    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.  2-9). 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  overhead  circuit  breaker panel (fig.  2-9). 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 failsafe indication in case one bulb burns out.  The circuit is protected by a 5-ampere circuit breaker,    placarded    LANDING    GEAR    IND,    on    the overhead circuit breaker panel (fig.  2-9). d. Landing Gear Warning Indicator Light Test Switch.      A   test   switch,   placarded   HDL   LT   TEST,   is located in the pilot's subpanel (fig.  2-8).  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   HORN,   on   the overhead circuit breaker panel (fig.  2-9). 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% N,, 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   and   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   cancelled. 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% N, 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 LDC GEAR WARN TEST  position  (fig.    2-8).    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 2-20