TM 1-1510-223-10 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 compartment doors. a. Cabin Door. Structural damage may occur if more than one person is present on the airstair cabin door at one time.  The door is weight limited to 300 pounds. An   airstair   door   (fig.      2-9),   hinged   at   the   bottom, provides a stairway for normal and emergency entrance and exit.  Two of the steps 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 a handhold  and  support  for  the  door  in  the  open  position 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  air-craft  is  pressurized  to  prevent  accidental unlatching   and/or   opening   of   the   door.      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  on  the caution/  advisory  panel  will  illuminate  if  the  door  is  not closed   and   all   latches   fully   locked.      The   cabin   door opening is 21.5 inches wide by 50.0 inches high. b. Cargo  Door.     A   swing-up   door   (fig.      2-9), hinged at the top, provides access for loading cargo or bulky  items.    The  cargo  door  opening  is  52.0  inches wide  by  52.0  inches  high.    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 or latch 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 with remote indication of cabin/cargo door security.  An annunciator placarded CABIN DOOR will illuminate if the cabin or cargo door is open and the BATTERY  switch  is  on.    If  the  BATTERY  switch  is  off, the  annunciator  will  illuminate  only  if  the  cabin  door  is not securely closed and latched.  The cabin/cargo door sensing circuit receives power from the hot battery bus. When operating the cargo door, ensure that the    cabin    door    is    closed    and    locked. Operating   the   cargo   door   while   the   cabin door  is  open  may  damage  the  door  hinge and adjacent structure. (1) Opening the cargo door. Avoid   side   loading   of   the   gas   springs   to prevent damage to the mechanism. 1. Handle access door (lower forward comer of door) - Unfasten and open. 2. Handle  -  Lift  hook  and  move  to OPEN position. 3. Handle access door - Secure. 4. Handle    access    door    (upper    aft comer   of   door)   -   Unfasten   and open. 2-17