TM 55-1510-222-10 reversible    type;    controlled    by    engine    oil    pressure through single action, engine driven propeller governors. The  propeller  is  flange  mounted  to  the  engine  shaft. Centrifugal   counterweights,   assisted   by   a   feathering spring,   move   the   blades   toward   the   low   RPM   (high pitch) position and into the feathered position. Governor boosted  engine  oil  pressure  moves  the  propeller  to  the high    RPM    (low    pitch)    hydraulic    stop    and    reverse position.    The  propellers  have  no  low  RPM  (high  pitch) stops;   this   allows   the   blades   to   feather   after   engine shutdown.  Low pitch propeller position is determined by the  low  pitch  stop  which  is  a  mechanically  actuated, hydraulic  stop.    Ground  fine  and  reverse  blade  angles are controlled by the power levers in the ground fine and reverse range. 2-42.  FEATHERING PROVISIONS. Both  manual  and  automatic  propeller  feathering systems are provided. Manual feathering is accomplished   by   pulling   the   corresponding   propeller lever   aft,   past   a   friction   detent.      To   unfeather,   the propeller   lever   is   pushed   forward   into   the   governing range.  The automatic feathering system will sense loss of   torque   and   will   feather   an   unpowered   propeller. Feathering  springs  will  feather  the  propeller  when  it  is not turning. a.          Automatic     Feathering.          The     automatic feathering   system   provides   a   means   of   immediately dumping   oil   from   the   propeller   servo   to   enable   the feathering spring and counterweights to start feathering action  of  the  blades  in  the  event  of  an  engine  failure. Although   the   system   is   armed   by   a   switch   on   the overhead    control    panel,    placarded    AUTOFEATHER TEST  OFF  ARM,  the  completion  of  the  arming  phase occurs   when   both   power   levers   are   advanced   above 89%    N.,    at    which    time    both    annunciators    on    the caution/advisory    annunciator    panel    indicate    a    fully armed system.  The annunciator panel annunciators are green  and  placarded  #1  AUTOFEATHER  (left  engine) and #2 AUTOFEATHER (right engine). The system will remain   inoperative   as   long   as   either   power   lever   is retarded   below   approximately   the   89%   N,   position, unless  TEST  position  of  the  AUTOFEATHER  switch  is selected to disable the power lever limit switches.  The system   is   designed   for   use   only   during   takeoff   or landing,   and   should   be   turned   off   when   establishing cruise   climb.      During   takeoff   or   landing,   should   the torque for either engine drop to an indication between 20 14%, the autofeather system for the opposite engine will be    disarmed.        Disarming    is    confirmed    when    the AUTOFEATHER annunciator of the opposite engine  becomes  extinguished.    If  torque  drops  further, to a reading between 13 and 7%, oil is dumped from the servo   of   the   affected   propeller   allowing   a   feathering spring  to  move  the  blades  into  the  feathered  position. Feathering also causes the AUTOFEATHER annunciator of the feathered propeller to extinguish.  At this     time,     both     the     #1     AUTOFEATHER     and     #2 AUTOFEATHER    annunciators    are    extinguished,    the propeller of the defective engine has feathered, and the propeller  of  the  operative  engine  has  been  disarmed from autofeathering capability.  Only manual feathering control remains for the second propeller. b.    Propeller  Autofeather  Switch.    Autofeathering is   controlled   by   the   AUTOFEATHER   switch   in   the overhead control panel (fig. 2-13). c.          Autofeather     Annunciators.          Autofeather annunciators  consist  of  two  green  annunciators  on  the caution/advisory annunciator panel placarded #I AUTOFEATHER    and    #2    AUTOFEATHER.        When illuminated, the annunciators indicate that the autofeather system is armed.  Both annunciators will be extinguished if either propeller has been feathered or if the   system   is   disarmed   by   retarding   a   power   lever. Autofeather   circuits   are   protected   by   one   5-ampere circuit  breaker  placarded  AUTO  FEATHER,  located  in the overhead circuit breaker panel (fig. 2-6). 2-43.  PROPELLER GOVERNORS. Two  governors,  a  constant  speed  governor,  and an  overspeed  governor,  control  propeller  RPM.    The constant    speed    governor,    mounted    on    top    of    the reduction   housing,   controls   the   propeller   through   its entire  range.    The  propeller  control  lever  controls  the propeller  by  means  of  this  governor.    If  the  constant speed  governor  should  malfunction  and  request  more than 1700 RPM, the overspeed governor cuts in at 1802 RPM and dumps oil from the propeller to keep the RPM from  exceeding  approximately  1802  RPM.  A  solenoid, actuated  by  the  GOVERNOR  TEST  switch  located  in the  overhead  control  panel  (fig.  2-13),  is  provided  for resetting the overspeed governor to approximately 1540 to 1580 RPM for test purposes.  If the propeller sticks or moves  too  slowly  during  a  transient  condition  causing the  propeller  governor  to  act  too  slowly  to  prevent  an overspeed     condition,     the     power     turbine     governor, contained  within  the  constant  speed  governor  housing, acts  as  a  fuel  topping  governor.    When  the  propeller reaches  106%  of  selected  N2RPM,  the  power  turbine governor   limits   the   fuel   flow   to   the   gas   generator, reducing 2-43