TM  55-1510-221  -10 tlons. activate ICE VANES if the temperature is below 15°C. d.    Taxing. Use normal procedures in Section II. 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 Use normal procedures in Section II. Avoid taking off in the wake of another alrcraft of the runway  surface  is  sandy  or  dusty. II. f.   During   Flight.      Use  normal  procedures  in  Section g. Descent.   Use normal procedures in Section II. h.    Landing.  Use  normal  procedures  in  Section  II. i.  Engine  Shutdown.  Use  normal  procedures  in Section II. CAUTION During hot weather. if fuel tanks are completely filled.  fuel  expansion  may  cause  overflow, thereby  creating  a  fire  hazard. j.  Before  Leaving  Aircraft.  Use  normal  procedures  in Section  II.  Take  extreme  care  to  prevent  sand  or  dust  from entering  the  fuel  and  oil  system  during  servicing.  During hot weather. release the brake immediately after installing wheel  chocks  to  prevent  brake  disc  warpage. 8-71.   TURBULENCE   AND   THUNDERSTORM OPERATION. CAUTION Due to the comparatively light wing loading, control in severe turbulence and thunderstorms is  critical. Since  turbulence  imposes  heavy loads   on   the   aircraft   structure.   make   all necessary  changes  in  aircraft  attitude  with  the least  amount  of  control  pressures  to  avoid excessive  loads  on  the  aircraft’s  structure. Thunderstorms  and  areas  of  severe  turbulence  should  be avoided. If such areas are to be penetrated. it will be necessary to counter rapid changes in attitude and accept major Indicated altitude variations. Penetration should be of  an  altitude  which  provides  adequate  maneuvering margins as a loss or gain of several thousand feet of altitude may be expected. The recommended penetration speed in severe turbulence is 158 KIAS. Pitch attitude and constant  power  settings  are  vital  to  proper  flight  technique. Establish recommended penetration speed and proper attitude prior to entering turbulent air to minimize most difficulties.  False  Indications  by  the  pressure  Instruments due to barometric pressure variations within the storm make  them  unreliable.  Maintaining  a  pre-established attitude  will  result  in  a  fairly  constant  airspeed.  Turn cockpit and cabin lights on to minimize the blinding effects of lighting. Do not use autopilot altitude hold. Maintaln constant power settings and pitch attitude regardless of airspeed  or  altitude  indications.  Concentrate  on  maintaining a level attitude by reference to the Flight Director/Attitude Indicator.  Maintain  original  heading.  Maker  no  turns unless   absolutely   necessary. 8-72.  ICE  AND  RAIN  (TYPICAL). WARNING While  in  icing  conditions.  if  there  is  an unexplained  30%  increase  of  torque  needed to   maintain   airspeed   in   level   flight,   a cumulative  total  of  two  or  more  inches  of  ice accumulation  on  the  wing,  an  unexplained decrease of 15 knots IAS. or an unexplained deviation   between   pilot’s   and   copilot’s airspeed   indicators,   the   icing   environment should be exited as soon as practicable. Ice accumulation  on  the  pitot  tube  assemblies could cause a complete loss of airspeed indication. The   following   conditions   indicate   a   possible accumulation of ice on the pitot tube assemblies and unprotected  aIrplane  surfaces. if any of these conditions are  observed.  the  icing  environment  should  be  exited  as soon  as  practicable. (1)  Total    ice  accumulation  of  two  inches  or  more  on the  wing  surfaces.  Determination  of  ice  thickness  can  be accomplished by summing the estimated ice thickness on the  wing  prior  to  each  pneumatic  boot  deice  cycle  (e.g.  four cycles  of  minimum  recommended  1/2-inch  accumulation. (2) A 30 percent Increase in torque per engine required to maintain a desired airspeed in level flight (not to  exceed  85  percent  torque)  when  operating  at recommended  holding/loiter  speed. (3) A decrease in Indicated airspeed of 15 knots after  entering  the  icing  condition  (not  slower  than  1.4 power off stall speed) if maintaining original power setting in Ievel flight. This can be determined by comparing pre- Change  5 8-28.1