TM 55-1510-219-10 2-8.  PARKING BRAKE. CAUTION Parking brakes shall not be set during flight. Dual parking brake valves are installed below the cockpit 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  left  subpanel.    Pulling  the  handle  full  out  sets  the check   valves   in   the   system   and   any   pressure   being applied by the toe brakes is maintained.  Parking brakes are released when the brake handle is pushed in.  The parking  brake  may  be  set  from  either  cockpit  position. Parking brakes shall not be set during flight. 2-9.  ENTRANCE AND EXIT PROVISIONS. NOTE Two   keys   are   provided   in   the   loose tools  and  equipment  bag.    Both  keys will  fit  the  locks  on  the  cabin  door, emergency hatch, tailcone access door    and    the    right    and    left    nose avionics doors. a. Cabin Door. CAUTION Structural  damage  may  be  caused  if more than one person is on the cabin door  at  a  time.    The  door  is  weight limited to less than 300 pounds. A   swing-down   door   (fig.      2-7),   hinged   at   the bottom,  provides  a  stairway  for  normal  and  emergency entry and exit.  Two of the steps are movable and fold flat against the door in the closed position.  A step folds down over the door sill when the door opens to provide a   platform   (step)   for   door   seal   protection.      A   plastic encased cable provides support for the door in the open position, a handhold, and a convenience for closing the door from inside.  A hydraulic damper permits the door to lower gradually during opening.  A rubber seal around the door seals the pressure vessel while the aircraft is in flight.      The   door   locking   mechanism   is   operated   by either  of  the  two  mechanically  interconnected  handles, one inside and  the  other  outside  the  door.    When  either  handle  is rotated, three rotating-cam-type latches on either side of the  door  capture  posts  mounted  on  the  cargo  door.    In the closed position, the door becomes an integral part of the  cargo  door.    A  button  adjacent  to  the  door  handle must be depressed before the handle can be rotated to open  the  door.    A  bellows  behind  the  button  is  inflated when  the  aircraft  is  pressurized  to  prevent  accidental unlatching  and/or  opening  of  the  door.    A  small  round window just above the second step permits observation of the pressurization safety bellows.  A placard adjacent to the window instructs the operator that the safety lock arm   is   in   position   around   the   bellows   shaft   which indicates a properly locked door.  Pushing the red button adjacent  to  the  window  will  illuminate  the  inside  door mechanism.    A  CABIN  DOOR  annunciator  light  in  the caution/advisory  panel  will  illuminate  if  the  door  is  not closed and all latches fully locked. b. Cargo Door.  A swing-up door (fig.  2-7), hinged at  the  top,  provides  cabin  access  for  loading  cargo  or bulky  items.    After  initial  opening  force  is  applied,  gas springs will completely open the cargo door automatically.      The   door   is   counterbalanced   and   will remain in the open position.  A door support rod is used to   hold   the   door   in   the   open   position,   and   to   aid   in overcoming  the  pressure  of  the  gas  spring  assemblies when  closing  the  door.    Once  closed,  the  gas  springs apply  a  closing  force  to  assist  in  latching  the  door.    A rubber  seal  around  the  door,  seals  the  pressure  vessel while in flight.  The door locking mechanism is operated only  from  inside  the  aircraft,  and  is  operated  by  two handles,  one  in  the  bottom  forward  portion  of  the  door and the other in the upper aft portion of the door.  When the upper aft handle is operated per placard instructions, two rotating cam-type latches on the forward side of the door   and   two   on   the   aft   side   rotate,   capturing   posts mounted on the fuselage side of the door opening.  The bottom  handle,  when  operated  per  placard  instructions, actuates  four  pin  lug  latches  across  the  bottom  of  the door.  A button on the upper aft handle must be pressed before the handle can be released to open the door.  A latching  lever  on  the  bottom  handle  must  be  lifted  to release   the   handle   before   the   lower   latches   can   be opened.      These   act   as   additional   aids   in   preventing accidental opening or unlatching of the door.  The cabin and cargo doors are equipped with dual sensing circuits to   provide   the   crew   remote   indication   of   cabin/cargo door  security.    An  annunciator  light  placarded  CABIN DOOR will illuminate if the cabin or cargo door is open and  the  BATT  switch  is  ON.    If  the  battery  switch  is OFF,  the  annunciator  will  illuminate  only  if  the  cargo door is not securely closed and latched.  The cargo door sensing circuit receives power from the hot battery bus. 2-15