TM 1-1510-218-10 8-29 are blocked, lowering the ice vanes will not rectify the condition.    Ice  vanes  should  be  retracted  at  +15  °C FAT and above to assure adequate engine oil cooling. (3)   Stalling  airspeeds  should  be  expected  to increase   when  ice   has   accumulated   on   the   aircraft causing  distortion  of  the  wing  airfoil.    For  the  same reason,   stall-warning   devices   are   not   accurate   and should not be relied upon.  Keep a comfortable margin of airspeed above the normal stall airspeed.  Maintain a    minimum    of    140    knots    during    sustained    icing conditions to prevent ice accumulation on unprotected surfaces of the wing.  In the event of windshield icing, reduce airspeed to 226 knots or below. h.    Descent.  Brake icing should be considered if  moisture  was  encountered  during  previous  ground operations   or   in   flight   in   icing   conditions   with   gear extended. i. Landing.  Landing on an icy  runway should be   attempted   only   when   absolutely   necessary   and should not be attempted unless the wind is within 10° of   runway   heading.      Application   of   brakes   without skidding  the  tires  on  ice  is  very  difficult,  due  to  the sensitive brakes.  In order  not  to  impair pilot  visibility, reverse   thrust   should   be   used   with   caution   when landing  on  a  runway  covered  with  snow  or  standing water. j. Engine  Shutdown.    Engine  shutdown   is the same as in normal conditions. k.     Before  Leaving  the  Aircraft.    When  the aircraft  is  parked  outside  on  ice  or  in  a  fluctuating freeze-thaw     temperature     condition,     the     following procedures  should  be  followed.    After  wheel  chocks are  in  place,  release  the  brakes  to  prevent  freezing. Fill  fuel  tanks  to  minimize  condensation,  remove  any accumulation   of   dirt   and   ice   from   the   landing   gear shock   struts,   and   install   protective   covers   to   guard against possible collection of snow and ice. 8-63.  DESERT  OPERATION  AND  HOT  WEATHER OPERATION. Dust,  sand,  and  high  temperatures  encountered during    desert    operation    can    sharply    reduce    the operational life of the aircraft and its equipment.  The abrasive  qualities  of  dust  and  sand  on  turbine  blades and  moving  parts  of  the  aircraft  and  the  destructive effect    of    heat    upon    the    aircraft    instruments    will necessitate  hours  of  maintenance  if  basic  preventive measures  are  not  followed.    In  flight,  the  hazards  of dust  and  sand  will  be  difficult  to  escape,  since  dust clouds  over  a  desert  may  be  found  at  altitudes  up  to 10,000   feet.      During   hot   weather   operations,   the principle difficulties encountered are high TGT's during engine   starting,   over-heating   of   brakes,   and   longer takeoff   and   landing   rolls   due   to   the   higher   density altitudes. In areas where high humidity is encountered, electrical equipment (such as communication   equipment   and   instruments)   will   be subject    to    malfunction    by    corrosion,    fungi,    and moisture absorption by nonmetallic materials. a.     Preparation for Flight. Check the position of  the  aircraft  in  relation  to  other  aircraft.    Propeller sandblast can damage closely parked aircraft.  Check that the landing gear shock struts are free of dust and sand.  Check instrument panel and general interior for dust  and  sand  accumulation.    Open  main  entrance door  and  cockpit  vent  storm  windows  to  ventilate  the aircraft. CAUTION N₁    speeds    of    70%    or    higher    may    be required   to   keep   oil   temperature   within limits. b.    Engine   Starting.      Engine   starting   under conditions of high ambient temperatures may produce a higher than normal TGT during the start.  The  TGT should  be  closely  monitored  when  the  condition  lever is    moved    to    the    LOW    IDLE    position.        If    over temperature tendencies are encountered, the condition lever   should   be   moved   to   IDLE   CUTOFF   position periodically during acceleration of gas generator RPM (N₁).        Be     prepared     to     abort     the     start     before temperature limitations are exceeded. c.     Warmup  Ground  Tests.    To  minimize  the possibility of damage to the engines during dusty/sandy conditions, activate ICE VANES. d.    Taxiing.     When   practical,   avoid   taxiing over  sandy  terrain  to  minimize  propeller  damage  and engine  deterioration  that  results  from  impingement  of sand  and  gravel.    During  hot  weather  operation,  use minimum braking action to prevent overheating. e.     Takeoff.    Avoid  taking  off  in  the  wake  of another aircraft if the runway surface is sandy or dusty. f. During Flight. During flight operation is the same as in normal conditions. g.    Descent. Descent operations are the same as in normal conditions. h.    Landing.  Landing operations are the same as in normal conditions. i. Engine  Shutdown.    Engine  shutdown   is the same as in normal conditions.