TM  55-1510-221-10 a. Cabin   Door. Structural  damage  may  be  caused  if  more than  one  person  is  on  the  cabin  door  at  a time.   The   door   is   weight   limited   to   300 pounds  or  less. A  swing-down  door  (fig.  2-9),  hinged  at  the  bot- tom,  provides  a  stairway  for  normal  and  emergency entrance  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  pro- tection.  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  gradu- ally  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   han- dles,   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  acciden- tal  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  opera- tor  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   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  sup- port  rod  is  used  to  hold  the  door  in  the  open  posi- tion,  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 2-16 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  han- dle  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 bat- tery   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. 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. Avoid  side  loading  of  the  gas  springs  to prevent  damage  to  the  mechanism. 1. 2. 3. 4. 5. Handle   access   door   (lower   for- ward   corner   of   door)   -Unfasten and  open. Handle  -  Lift  hook  and  move  to OPEN   position. Handle  access  door  -  Secure. Handle  access  door  (upper  aft  cor- ner  of  door)  -  Unfasten  and  open. Handle  -  Press  button  and  lift  to OPEN  position  then  latch  in place.