TM 55-1510-222-10 overhead    circuit    breaker    panel    (fig.    2-6),    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  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, 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 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. 2-5). The control switch and   associated   relay   circuits   are   protected   by   a   2- ampere   circuit   breaker,   placarded   LANDING   GEAR CONTROL located in the overhead circuit breaker panel (fig. 2-6). b. Landing  Gear  Down  Position  Annunciators. Visual indication of the landing gear position is provided by  three,  individual,  green  GEAR  DOWN  annunciators located in the left subpanel.  Testing of the annunciators 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. 2-6). c. Landing Gear Position Warning Annunciators.        Two    red    parallel-wired    annunciators, located  in  the  LDG  GEAR  CONTROL  switch  handle, illuminate to show that the gear is in transit or unlocked. The red annunciator in the handle also illuminates when the  landing  gear  warning  horn  is  actuated.    Both  red annunciators  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 (fig. 2-6). d. Landing    Gear    Warning    Annunciator    Test Switch.      A   test   switch,   placarded   HDL   LT   TEST,   is located  in  the  pilot's  subpanel  (fig.  2-5).    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. 2-6). 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   with   either   or   both   power levers    retarded    below    approximately    84%    N1,    the warning   horn   will   sound   and   the   landing   gear   switch handle  annunciators  will  illuminate.    The  horn  can  be silenced    by    actuating    the    GEAR    WARN    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  magneticlly  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 2-11