TM 1-1510-225-10 8A-27 The surface of the aircraft must be at a temperature of freezing  or  below  for  ice  to  stick.    If   severe   icing conditions   are   encountered,   ascend   or   descend   to altitudes where these conditions do not prevail.  If flight into   icing   conditions   is   unavoidable,   proper   use   of aircraft  anti-icing  and  deicing  systems  may  minimize the problems encountered.  Approximately 15 minutes prior  to  flight  into  temperature  conditions  which  could produce  frost  or  icing  conditions,  the  pilot  and  copilot windshield anti-ice switches should be set at NORMAL or  HIGH  temperature  position  (after  preheating)   as necessary    to    eliminate    windshield    ice.        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   with   ice   on   the   aircraft. 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. b.  Rain.    Rain  presents  no  particular  problems other  than  slippery  runways,  restricted  visibility,  and occasional incorrect airspeed indications. c.   Taxiing.    Extreme  care  must  be  exercised when  taxiing  on  ice  or  slippery  runways.    Excessive use   of   either   brakes   or   power   may   result   in   an uncontrollable skid. d.  Takeoff.    Extreme  care  must  be  exercised during takeoff from ice or slippery runways.  Excessive use   of   either   brakes   or   power   may   result   in   an uncontrollable skid. e.   Climb.      Keep   aircraft   attitude   as   flat   as possible and climb with higher airspeed than usual, so that the lower surfaces of the aircraft will not be iced by flight at a high angle of attack. f.   Cruise Flight.  Prevention of ice formation is far  more  effective  and  satisfactory  than  attempts  to dislodge the ice after it has formed.  If icing conditions are  inadvertently  encountered,  turn  on  the  anti-icing systems prior to the first sign of ice formation.  Do not operate  deicer  boots  continuously.    Allow  at  least  1/2 inch  of  ice  on  the  wing  deicer  boots  before  activating the   deicer   boots.      Continued   flight   in   severe   icing conditions should not be attempted.  If ice forms on the wing area aft of the deicer boots, climb or descend to an altitude where conditions are less severe. g.  Landing.    Extreme  care  must  be  exercised when  landing  on  ice  or  slippery  runways.    Excessive use   of   either   brakes   or   power   may   result   in   an uncontrollable  skid.    Ice  accumulation  on  the  aircraft will   result   in   higher   stalling   airspeeds   due   to   the change  in  aerodynamic  characteristics  and  increased weight of the aircraft due to ice buildup.  Approach and landing airspeeds must be increased accordingly. 8A-60.  ICING (SEVERE). a.   The   following   weather   conditions   may   be conducive to severe in-flight icing: 1.  Visible  rain  at  temperatures  below  0 C ambient air temperature. 2.  Droplets  that  splash  or  splatter  on  impact at  temperatures  below  0 C  ambient  air temperature. b.  The following procedures for exiting a severe icing  environment  are  applicable  to  all  flight  phases from takeoff to landing: 1.  Monitor    the    ambient    air    temperature. While severe icing may form at temperatures as cold as –18 C, increased vigilance   is   warranted   at   temperatures around    freezing    with    visible    moisture present. 2.  Upon  observing  the  visual  cues  specified in the limitations section of this manual for the identification of severe icing conditions, Paragraph 5-35, accomplish the following: a.  Immediately   request   priority   handling from   air   traffic   control   to   facilitate   a route  or  an  altitude  change  to  exit  the severe icing conditions in order to avoid extended  exposure  to  flight  conditions more  severe  than  those  for  which  the aircraft has been certified. b.  Avoid abrupt and excessive maneuvering     that     may     exacerbate control difficulties. c.   Do not engage the autopilot. d.  If  the  autopilot  is  engaged,  hold  the control wheel firmly and disengage the autopilot. e.  If an unusual roll response or uncommanded roll control movement is observed reduce the angle-of-attack. f.    Do  not  extend  flaps  during  extended operation in icing conditions.