TM 55-1510-220-10 inside  door  mechanism.    A  CABIN  DOOR  annunciator 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 50.0 inches high. b. Cargo Door.  A swing-up door (fig.  2-9), 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 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  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 in 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. The   cargo   door   opening   is   52.0   inches   wide   by   52.0 inches high. CAUTION Insure 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 cargo door. CAUTION Avoid    side    loading    of    the    gas springs  to  prevent  damage  to  the mechanism. 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. 4.  Handle access door (upper aft corner of door) Unfasten and open. 5.  Handle Press button and lift to OPEN position then latch in place. 6.  Handle access door Secure. 7.    Door  support  rod  Attach  one  end  to cargo door ball stud (on forward side of door). 8.  Support rod detent pin Check in place. 9.    Cabin  door  sill  step  Push  out  on  and allow    cargo    door    to    swing    open.        Gas    springs    will automatically open the door. 10.    Door  support  rod  Attach  free  end  to ball stud on forward fuselage door frame. (2) Closing cargo door. CAUTION Avoid    side    loading    of    the    gas springs  to  prevent  damage  to  the mechanism. 1.          Door     support     rod     Detach     from fuselage door frame ball stud, then firmly grasp free end of  rod  while  exerting  downward  force  to  overcome  the pressure of gas spring assemblies, Then remove support rod from door as gas spring assemblies pass over-center position. 2.  Cargo door - Pull closed, using finger hold cavity in fixed cabin door step. 2-17