TM 1-1510-225-10 2-27 2-9.  ENTRANCE AND EXIT PROVISIONS. NOTE Two  keys  are  provided  in  the  loose  tools and equipment bag.  Both keys fit the locks on    the    cabin    door,    emergency    hatch, tailcone access door, and the right and left nose avionics compartment doors.  a.   Cabin Door. CAUTION 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   cabin   door,   hinged   at   the   bottom, provides    a    stairway,    for    normal    and    emergency entrance and exit.  Refer to Figure 2-8.  In the closed position,   the   door   becomes   an   integral   part   of   the cargo door.  The cabin door is provided with steps, two of   which   fold   flat   against   the   door   in   the   closed position.  A step folds down over the doorsill when the door  opens  to  provide  a  platform  (step)  for  door  seal protection.     T3    F3 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.      R    Two    plastic-encased   cables   provide   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   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.   A button adjacent to the door handle must be pressed 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 placard adjacent to the window instructs  the  operator  that  the  safety  lock  arm  is  in position   around   the   bellows   shaft   that   indicates   a properly locked door.  Pushing the red button adjacent to the window will illuminate the inside door mechanism.  T3 F3 A DOOR UNLOCKED annunciator on the caution/advisory panel will illuminate if the door is not closed and all latches fully locked.    R A  DOOR UNLOCKED   warning   light   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 46.0 inches high. b.  Cargo Door.  A swing-up cargo door, hinged at the top, provides  access for loading cargo or bulky items.  Refer to Figure 2-8.  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 counter-balanced 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,  cam-type latches  (two  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 DOOR   UNLOCKED,   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/cargo   door   is   not   securely   closed   and latched.  The cabin/cargo door sensing circuit receives power from the hot battery bus. CAUTION 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. To   prevent   damage   to   the   mechanism, avoid side loading of the gas springs.  (1)   Opening the Cargo Door. 1.   Handle  Access  Door  (lower  forward corner of door)  – Unfasten and open. 2.   Handle  – Lift hook and move to OPEN position. 3.   Handle Access Door – Secure.