TM  55-1510-221-10 Table  2-3.  Fuel  Sump  Drain  Locations NUMBER DRAINS LOCATION 1 Leading  Edge  Tank Outboard  of  nacelle,  underside  of  wing 1 Integral   Tank Underside  of  wing,  forward  of  aileron 1 Firewall   Fuel   Filter Underside  of  cowling  forward  of  firewall 1 Sump   Strainer Bottom  center  of  nacelle  forward  of  wheel  well 1 Gravity   Feed   Line Aft  of  wheel  well 1 Auxiliary   Tank At  wing  root,  just  forward  of  the  flap tion.  An  internal  float  switch  actuates  an  electric scavenger  pump  which  delivers  the  fuel  to  the  fuel purge  line  just  aft  of  the  fuel  purge  shutoff  valve.  A check  valve  in  the  line  prevents  the  backflow  of  fuel during  engine  purging.  The  circuit  breaker  for  both pumps  is  located  in  the  fuel  section  of  the  overhead circuit   breaker   panel;   placarded   SCAVENGER PUMP.   A   vent   line,   plumbed   from   the   top   of   the collector   tank,   is   routed   through   an   inline   flame arrestor  and  then  downward  to  a  drain  manifold  on the  underside  of  the  nacelle. fer  of  auxiliary  fuel,  which  is  automatically  con- trolled,  the  nacelle  tanks  are  maintained  full.  A check   valve   in   the   gravity   feed   line   from   the   out- board  wing  prevents  reverse  fuel  flow.  Normal  grav- ity  transfer  of  the  main  wing  fuel  into  the  nacelle tanks   will   begin   when   auxiliary   fuel   is   exhausted. The  system  will  gravity  feed  fuel  only  to  its  respec- tive  nacelle  tank,  i.e.  left  or  right  (fig.  2-16).  Fuel will  not  gravity  feed  through  the  crossfeed  system. i.   Fuel   Vent   System.  Each  fuel  system  is vented  through  two  ram  vents  located  on  the  under- side  of  the  wing  adjacent  to  the  nacelle.  To  prevent icing  of  the  vent  system,  one  vent  is  recessed  into the   wing   and   the   backup   vent   protrudes   out   from the  wing  and  contains  a  heating  element.  The  vent line  at  the  nacelle  contains  an  inline  flame  arrestor. j.  Engine  Oil-to-Fuel  Heat  Exchanger.  A n engine  oil-to-fuel  heat  exchanger,  located  on  each engine   accessory   case,   operates   continuously   and automatically  to  heat  the  fuel  delivered  to  the  engine sufficiently   to   prevent   the   freezing   of   any   water which  it  might  contain.  The  temperature  of  the delivered  fuel  is  thermostatically  regulated  to  remain between  21°C  and  32°C. b.  Operation  With  Failed  Engine-Driven  Boost Pump   or   Standby   Pump.   Two  pumps  in  each  fuel system  provide  inlet  head  pressure  to  the  engine- driven  primary  high-pressure  fuel  pump.  If  crossfeed is  used,  a  third  pump,  the  standby  fuel  pump  from the  opposite  system,  will  supply  the  required  pres- sure.  Operation  under  this  condition  will  result  in  an unbalanced  fuel  load  as  fuel  from  one  system  will  be supplied  to  both  engines  while  all  fuel  from  the  sys- tem  with  the  failed  engine  driven  and  standby  boost pumps  will  remain  unused.  A  triple  failure,  which  is highly  unlikely,  would  result  in  the  engine  driven primary   pump   operating   without   inlet   head   pres- sure.  Should  this  situation  occur,  the  affected  engine can  continue  to  operate  from  its  own  fuel  supply  on its   engine-driven   primary   high-pressure   fuel   pump. 2-34. FUEL SYSTEM MANAGEMENT. 2-35. FERRY FUEL SYSTEM. a.   Fuel   Transfer   System.   When   the   auxiliary tanks  are  filled,  they  will  be  used  first.  During  trans- Provisions   are   installed   for   connection   to   long range  fuel  cells. Section  V.  FLIGHT  CONTROLS 2-36. DESCRIPTION. The   aircraft’s   primary   flight   control   systems consist  of  conventional  rudder,  elevator  and  aileron control  surfaces.  These  surfaces  are  manually  oper- ated  from  the  cockpit  through  mechanical  linkage using  a  control  wheel  for  the  ailerons  and  elevators, and   adjustable   rudder/brake   pedals   for   the   rudder. Both  the  pilot  and  copilot  have  flight  controls.  Trim control   for   the   rudder,   elevator   and   ailerons   is accomplished   through   a   manually   actuated   cable- drum   system   for   each   set   of   control   surfaces.   The autopilot  has  provisions  for  controlling  the  position of   the   ailerons,   elevators,   and   rudder.   Chapter   3 describes  the  operation  of  the  autopilot  system. 2-34