TM 1-1510-223-10 shock  struts  are  extended  (normally  after  takeoff),  or compressed (normally after landing).  The safety switch on   the   right   main   landing   gear   strut   deactivates   the landing     gear     control     circuits,     cabin     pressurization circuits, and the flight hour meter when the shock strut is compressed.      This   switch   also   activates   a   downlock hook,   preventing   the   landing   gear   from   being   raised while  the  aircraft  is  on  the  ground.    The  hook,  which unlocks   automatically   after   takeoff,   can   be   manually overridden    by    pressing    down    on    the    red    button, placarded    DN    LOCK    REL    located    adjacent    to    the landing gear handle (fig.  2-6).  If the override is used, the  landing  gear  warning  horn  will  sound  intermittently and two red parallel-wired indicator lights located in the landing    gear    control    switch    handle    will    illuminate, provided the BATTERY switch is on.  The safety switch on the left main landing gear strut activates the left and right engine ambient air shut-off valves when the strut is extended. h. Landing Gear Alternate Extension. After  an  emergency  landing  gear  extension has  been  made,  do  not  move  any  landing gear    controls,    or    reset    any    switches    or circuit breakers until the aircraft is on jacks. The  failure  may  have  been  in  the  gear-up circuit which could cause the gear to retract while the aircraft is on the ground. If   for   any   reason   the   three   green   GEAR DOWN   indicator   lights   do   not   illuminate (e.g., in case of an electrical system failure), continue  pumping  until  sufficient  resistance is  felt  to  ensure  that  the  gear  is  down  and locked.  Do not stow the hand pump handle. Stowing   the   handle   will   release   hydraulic pressure.        If    the    three    GEAR    DOWN indicator    lights    are    not    illuminated,    the landing gear downlocks may not be engaged and hydraulic pressure may be the only thing holding the landing gear down. An   extension   lever,   placarded   LANDING   GEAR ALTERNATE    EXTENSION,    is    located    on    the    floor between the crew seats.  A manual pumping action with the   handle   lowers   the   landing   gear.      The   hydraulic pump,  which  is  utilized  to  manually  lower  the  gear  is located under the floor. To  engage  the  system,  pull  the  LANDING  GEAR CONTROL   circuit   breaker,   located   on   the   overhead circuit breaker panel (fig.  2-7), and ensure that the LDG GEAR  CONTR  handle  is  in  the  DN  position.    Remove the extension lever from the securing clip and pump the lever  up  and  down  until  the  three  green  GEAR  DOWN indicator   lights   illuminate.      As   the   handle   is   moved, hydraulic fluid is drawn from the hand pump suction port of  the  power  pack  and  routed  through  the  hand  pump pressure   port   to   the   actuators.      After   an   alternate extension of the landing gear, ensure that the extension lever  is  in  the  full  down  position  prior  to  stowing  the pump   handle   in   the   retaining   clip.      When   the   pump handle is stowed, an internal relief valve is actuated to relieve the hydraulic pressure in the pump. After    a    practice    alternate    extension,    stow    the extension handle, reset the LANDING GEAR CONTROL circuit   breaker,   and   retract   the   gear   in   the   normal manner with the landing gear control handle. i. Tires.  The aircraft is equipped with dual 22 x 6.75  x  10,  8  ply  rated,  tubeless  rim-inflation  tires  on each  main  gear  and  a  22  x  6.75  x  10,  8  ply  rated, tubeless tire on the nose wheel. j. Steerable    Nose    Wheel.        The    aircraft    is maneuvered on the ground by the steerable nose wheel system.  Direct linkage from the rudder pedals (fig.  2-8) to the nose wheel steering linkage allows the nose wheel to be turned 12°  to the left of center or 14°  to the right. When   rudder   pedal   steering   is   augmented   by   main wheel  braking  action,  the  nose  wheel  can  be  deflected up to 48°  either side of center.  Shock loads which would normally    be    transmitted    to    the    rudder    pedals    are absorbed by a spring mechanism in the steering linkage. Retraction of the landing gear automatically centers the nose  wheel  and  disengages  the  steering  linkage  from the rudder pedals. k. Wheel Brake System.   The main wheels are equipped  with  multiple-disc  hydraulic  brakes,  actuated by master cylinders attached to the toe brake sections of the rudder pedals.  Brake fluid is supplied to the system from  a  reservoir  in  the  nose  compartment  Braking  is permitted    from    either    set    of    rudder    pedals.        No emergency    brake    system    is    provided.        Repeated application    of    brakes    with    insufficient    cooling    time between    applications    will    cause    a    loss    of    braking efficiency,  and  may  cause  brake  or  wheel  failure,  tire blowout, or destruction of wheel assembly by fire. 2-8.    PARKING BRAKE. Dual parking brake valves are installed below the cock-pit floor. Both valves can be closed simultaneously by pressing both brake pedals to build up pressure,     then     pulling     out     the     handle     placarded PARKING  BRAKE,  on  the  pilot's  subpanel  (fig.    2-6). Pulling  the  handle  full  out  sets  the  check  valves  in  the system   and   any   pressure   being   applied   by   the   toe brakes   is   maintained   The   parking   brake   is   released when the brake handle is pushed in.  The parking brake may  be  set  from  either  cockpit  position.    The  parking brake shall not be set during flight. 2-15