TM 55-1510-220-10 WARNING Pressurized flight is prohibited due to a cracked windshield.  Conduct flight with the  CABIN  PRESS  switch  in  the  DUMP position   and   the   BLEED   AIR   VALVE switches  in  the  ENVIRO  OFF  or  PNEU ONLY position. NOTE For    further    information    on    cracked windshield   procedures,   see   the   RC-12 Series Maintenance Manual. Section VIII.  OTHER LIMITATIONS 5-35.  MAXIMUM DESIGN SINK RATE. The  maximum  design  sink  rate  below  13,500  lbs. gross   weight   is   600   feet   per   minute.      The   maximum design  sink  rate  above  13,500  lbs.  gross  weight  is  480 feet per minute. 5-36.  INSTRUMENT LANDING SYSTEM LIMITS. During  ILS  approach  do  not  operate  the  propellers in the 1750 to 1850 RPM range. 5-37.  INTENTIONAL ENGINE CUT SPEED. Inflight   engine   cuts   below   the   safe   one-engine inoperative speed (Vsse, 107 KIAS) are prohibited. 5-38.  LANDING ON UNPREPARED RUNWAY. CAUTION Except    in    an    emergency,    propellers should  be  moved  out  of  reverse  above 40   knots   to   minimize   propeller   blade erosion, and during crosswind to minimize  stress  imposed  on  propeller, engine   and   airframe.      Care   must   be exercised   when   reversing   on   runways with loose sand or dust on the surface. Flying    gravel    will    damage    propeller blades  and  dust  may  impair  the  pilot's forward visibility at low aircraft speeds. 5-39.  MINIMUM OIL TEMPERATURE REQUIRED FOR FLIGHT. Engine oil is used to heat the fuel upon entering the fuel   control.      Since   no   temperature   measurement   is available for the fuel at this point, it must be assumed to be the same as the FAT.  The minimum oil temperature graph (fig.  5-3) is provided for use as a guide in preflight planning, based on known or forecast operating conditions,   to   allow   the   operator   to   become   aware   of operating   temperatures   where   icing   at   the   fuel   control could    occur.        If    the    plot    should    indicate    that    oil temperatures   versus   FAT   are   such   that   ice   formation could occur during take-off or in flight, anti-icing additive per MILI-27686 should be mixed with the fuel at refueling to  insure  safe  operation.    In  the  event  that  authorized fuels  (Prist)  are  not  available  the  limitation  of  this  chart apply. CAUTION Anti-icing    additive    must    be    properly blended with the fuel to avoid deterioration    of    the    fuel    cell.        The additive  concentration  by  volume  shall be     a     minimum     of     0.060%     and     a maximum of 0.15%. Approved procedure for adding anti-icing concentrate  is  contained  in  Chapter  2, Section XII. JP-4 fuel per MILT-5624 has anti-icing additive per MILI-27686  blended  in  the  fuel  at  the  refinery  and  no further treatment is necessary.  Some fuel suppliers blend anti-icing    additive    in    their    storage    tanks.        Prior    to refueling, check with the fuel supplier to determine if fuel has  been  blended.    To  assure  proper  concentration  by volume  of  fuel  on  board,  blend  only  enough  additive  for the unblended fuel. Change 2 5-11