switch to shutoff the power to the hoist motor and electric brake. Loss of electric power causes the brake to automatically stop the elevator. If the brake fails to stop the elevator, the governor sheave grips the governor rope, causing the broken-rope safety device to stop the elevator. A slack, cable sensing, safety device is provided for each suspension rope and the governor rope. Located in the  area  between  the  winch  drums  and  the  overhead sheaves, these devices function by applying a spring-loaded  follower  roller  to  the  wire  rope.  Rope slack  causes  a  proximity  switch  to  shutoff  electrical power  to  the  hoisting  winch  motor  and  brake,  which stops the elevator. If  the  elevator  over  travels  upward  beyond  the maximum up stop position, an over travel limit switch is  actuated.  This  stops  the  elevator  by  shutting  off power to the hoisting winch motor and brake. If  the  elevator  over  travels  downward  beyond  the hold deck loading station level, spring bumpers in the bottom  of  the  elevator  trunk  stop  the  platform.  The slack-cable switches are actuated to cut off power to the hoisting winch motor and brake. An operator-attended control panel is located next to all elevator doors. All operator control panels have a display of selector switches, push buttons, and indicator lamps  suited  for  the  control  functions  required  at  the station  served.  All  control  panels  have  an  emergency stop-run   switch   from   which   all   operations   of   the elevator can be stopped. The   main   operator   control   panel   and   electrical power switch are located at the 2nd deck-level station. An elevator can be dispatched to another level from any operator control panel. The lower-stage elevator control system   can   dispatch   the   elevator   to   another   level. However,  it  can't  retrieve  the  elevator  from  another level. IMPROVED WEAPONS HANDLING SYS- TEM (IWHS) LOWER-STAGE WEAPONS ELEVATORS.—The    IWHS    lower-stage    weapons elevator (fig. 11-11) services magazines and ammunition handling areas from the 7th deck level up to  and  including  the  main  deck  (hangar  deck).  The IWHS is a highly sophisticated system controlled by a PDP-14    programmable    controller    that    continually tracks the location of the platform to within one-twelfth of  an  inch.  Because  of  the  complexity  of  the  IWHS, elevator   operators   and   maintenance   personnel   are extensively    trained    in    hydraulics,    electricity,    and electronics. Four cables attached at the corners lift the platform. The platform machinery is located at the 3rd deck level. The    hatches    are    opened    hydraulically.    They    are designed to automatically undog-open-latch and unlatch-close-dog. The elevator doors are also operated hydraulically. The    IWHS    incorporates    the    following    safety features:   An over speed governor slack-cable device   An over speed governor device   A  hydraulic  interlock  to  prevent  two  hatches from being opened at the same time   A  hydraulic  interlock  to  prevent  hatches  from closing when dogs are in the dogged position   An   electrical   interlock   to   prevent   opening   a magazine door unless the platform is at that level   An electrical interlock to prevent opening more than one magazine door at a time   A  pressure  switch  to  prevent  operation  of  the elevator  when  the  hydraulic  pressure  is  below 1,200 psi 11-19 Figure 11-11.—Typical IWHS lower-stage, weapons elevator.