TM 1-1510-224-10 extended    range    system    is    in    use,    of    the    preflight inspection  includes  draining  a  small  amount  of  fuel  from this drain to check for fuel contamination.  Whenever the extended range system is removed from the aircraft and the  fuel  line  is  capped  off  in  the  fuselage,  the  remaining fuel in the line shall be drained. h.  Fuel Purge System.   Each engine is provided with  a  fuel  purge  system.    The  system  is  designed  to ensure   that   any   residual   fuel   in   the   fuel   manifolds   is consumed    during    engine    shutdown.        During    engine operation,  compressor  discharge  air  is  routed  through  a filter   and   check   valve,   pressurizing   a   small   air   tank mounted  on  the  engine  truss.    On  engine  shutdown  the pressure    differential    between    the    air    tank    and    fuel manifolds causes air to be discharged from the air tank, through  a  check  valve,  and  into  manifolds,  out  through the  nozzles  and  into  the  combustion  chamber.    The  fuel forced    into    the    combustion    chamber    is    consumed, causing a momentary rise in engine TGT. i.      Fuel   Vent   System.      Each   fuel   system   is vented through two ram vents located in the underside of the  wing  adjacent  to  the  nacelle,  and  a  secondary  vent, located in the aileron cove near the wing tip.  To prevent icing  of  the  vent  system,  one  vent  is  recessed  into  the wing and the other ram vent protrudes out from the wing and  contains  a  heating  element.    The  vent  line  at  the nacelle contains an inline flame arrester. j.      Engine   Oil-to-Fuel   Heat   Exchanger.      An engine  oil-to-fuel  heat  exchanger,  one  located  on  each engine   accessory   case,   operates   continuously   during engine  operation  to  heat  fuel  delivered  to  the  engine  to prevent the freezing of water which the fuel may contain 3hl.Fuel System Management. k.    Fuel  Transfer  System.    When  the  auxiliary tanks are filled, they will be used first.  During transfer of auxiliary    fuel,    which    is    automatically    controlled,    the nacelle  tanks  are  maintained  full.    A  check  valve  in  the gravity    feed    line    from    the    outboard    wing    prevents reverse  fuel  flow.    Normal  gravity  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 respective nacelle tank, i.e., left or right (fig. 2-22). Fuel will not gravity feed through the crossfeed system. I.    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   pressure.      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   system   with   the   failed engine-driven   and   standby   boost   pumps   will   remain unused. 2-33.  FERRY FUEL SYSTEM. Provisions   are   installed   for   connection   to   long range fuel cells. 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 flap 1 Extended Range Outboard of fuselage on underside of wing center section BT001965 2-49