TM   1-1510-223-10 f.    During    Flight.    Use   normal   procedures   in   Section II. 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. 8-50.   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  150  KIAS.  Constant  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. Maintain   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. 8-51. 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. a.   Typical   Ice.   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  ½-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  level  flight.  This  can  be  determined  by  comparing  pre- icing  condition  entry  speed  to  the  indicated  speed  after  a surface and antenna deice cycle is completed. (4)   Any  variations  from  normal  indicated  airspeed between the pilot’s and copilot’s airspeed indicators. Icing  occurs  because  of  supercooled  water  vapor  such as  fog,  clouds  or  rain.  The  most  severe  icing  occurs  on aircraft  surfaces  in  visible  moisture  or  precipitation  with  a true   outside   air   temperature   between   -5°C   and   +l°C. However,   under   some   circumstances,   dangerous   icing conditions   may   be   encountered   with   temperatures   below -10°C. The surface of the aircraft must be at a temperature of  freezing  or  below  for  it  to  stick.  If  severe  icing 8-32 Change  1