TM  55-1510-221-10 a.    Landing    Gear    Down    Position-Indicator Lights.   Landing  gear  down  position  is  indicated  by three  green  lights  on  the  left  subpanel,  placarded GEAR   DOWN.   These   lights   may   be   checked   by operating   the   ANNUNCIATOR   TEST   switch.   The circuit   is   protected   by   a   5-ampere   circuit   breaker, placarded  LANDING  GEAR  IND,  on  the  overhead circuit breaker panel (fig. 2-26). b.   Landing   Gear   Position   Warning   Lights. Two   red   bulbs,   wired   in   parallel   and   activated   by microswitches   independent   of   the   GEAR   DOWN position  indicator  lights,  are  positioned  inside  the clear  plastic  grip  on  the  landing  gear  control  switch. These  lights  illuminate  whenever  the  landing  gear switch  is  in  either  the  UP  or  DN  position  and  the gear  is  in  transit.  Both  bulbs  will  also  illuminate should  either  or  both  power  levers  be  retarded  below approximately  79  to  81%  N₁ when  the  landing  gear is  not  down  and  locked.  To  turn  the  switch  lights OFF  during  single-engine  operation,  the  power  lever for  the  inoperative  engine  must  be  advanced  to  a position  which  is  higher  than  the  setting  of  the  warn- ing  horn  microswitch.  Extending  the  landing  gear will  also  turn  the  lights  off.  Both  red  lights  indicate the  same  warning  conditions,  but  two  are  provided for  a  fail-safe  indication  in  the  event  one  bulb  burns out.  The  circuit  is  protected  by  a  5-ampere  circuit breaker,   placarded   LANDING   GEAR   IND,   on   the overhead  circuit  breaker  panel  (fig.  2-26). c.  Landing  Gear  Warning  Light  Test  Button. A  test  button,  placarded  HDL  LT  TEST,  is  located on  the  left  subpanel.  Failure  of  the  landing  gear switch  to  illuminate  red,  when  this  test  button  is pressed,   indicates   two   defective   bulbs   or   a   circuit fault.  The  circuit  is  protected  by  a  5-ampere  circuit breaker,   placarded   LANDING   GEAR   RELAY CONTROL,   on   the   overhead   circuit   breaker   panel (fig.  2-26). d.  Landing  Gear  Warning  Horn.  When  either power  lever  is  retarded  below  approximately  79  to 81  N,  when  the  landing  gear  is  not  down  and  locked or  if  the  flaps  are  extended  beyond  40%  and  the landing  gear  is  not  down  and  locked,  a  warning  horn located   in   the   overhead   control   panel   will   sound intermittently.  To  prevent  the  warning  horn  from sounding  during  long  descents  or  an  ILS  approach, a  pressure  differential  “Q”  switch  is  connected  into the   copilot’s   static   line.   The   switch   prevents   the warning  horn  from  sounding  until  airspeed  drops below  140  KIAS.  An  altitude  sensing  switch  is installed   in   series   with   the   140   KIAS   “Q“   switch which   prevents   the   warning   horn   from   sounding after  climbing  through  12,500  feet  MSL.  The  horn will  be  engaged  when  the  aircraft  descends  through 10,500  MSL.  The  warning  horn  circuit  is  protected by  a  5-ampere  circuit  breaker,  placarded  LANDING GEAR  WARN,  on  the  overhead  circuit  breaker panel (fig. 2-26). e.  Landing  Gear  Warning  Horn  Test  Switch. The  landing  gear  warning  horn  may  be  tested  by  the test  switch  on  the  right  subpanel  (fig.  2-6).  The switch,  placarded  STALL  WARN  TEST  -  OFF  - LDG  GEAR  WARN  TEST,  will  sound  the  landing gear   warning   horn   and   illuminate   the   landing   gear position  warning  lights  when  moved  to  the  momen- tary  LDG  GEAR  WARN  TEST  position.  The  circuit is  protected  by  a  5-ampere  circuit  breaker,  placarded LANDING  GEAR  WARN,  on  the  overhead  circuit breaker  panel  (fig.  2-26). f.   Landing   Gear   Safety   Switches.   A    safety switch  on  each  main  landing  gear  shock  strut  con- trols   the   operation   of   various   aircraft   systems   that function  only  during  flight  or  only  during  ground operation.  These  switches  are  mechanically  actuated whenever  the  main  landing  gear  shock  struts  are extended   (normally   after   takeoff),   or   compressed (normally   after   landing).   The   safety   switch   on   the right   main   landing   gear   strut   activates   the   landing gear  control  circuits,  cabin  pressurization  circuits and  the  flight  hour  meter  flight  time  function  on  the copilot’s   clock   when   the   strut   is   extended.   This switch   also   activates   a   down-lock   hook,   preventing the  landing  gear  from  being  raised  while  the  aircraft is  on  the  ground.  The  hook,  which  unlocks  automat- ically  after  takeoff,  can  be  manually  overridden  by pressing   down   on   the   red   button,   placarded   DN LOCK  REL  located  adjacent  to  the  landing  gear switch.  If  the  override  is  used  and  the  landing  gear control  switch  is  raised,  power  will  be  supplied  to the   warning   horn   circuit   and   the   horn   will   sound. The  safety  switch  on  the  left  main  landing  gear  strut activates  the  left  and  right  engine  ambient  air  shut- off  valves  when  the  strut  is  extended. g.   Landing   Gear   Alternate   Engage   Handle. During   manual   landing   gear   extension,   the   landing gear  motor  must  be  disengaged  from  the  landing gear   drive   mechanism.   This   is   accomplished   by   a manually-operated   clutch   disengage   lever   (fig.   2-7) located  adjacent  to  the  landing  gear  alternate  exten- sion  handle  (fig.  2-7).  To  disengage  the  clutch,  pull the  alternate  engage  handle  up  and  turn  clockwise. To  engage  the  clutch,  turn  the  alternate  engage  han- dle  counterclockwise  and  release. 2-12