Icing Conditions

'Icing' or 'icing conditions' are a source of hazard to aviation. When accumulating on the airplane structures, ice is decreasing lift and thrust and increasing drag and weigth which brings to degradated performance. Icing also is impacting gauge display, commands or seriously can compromise the engine working. Ice may exist under three forms mainly. Ice proper is transparent, heavy, swift to form and hard to remove. Frost is a lighter, whitish deposit as it is more nefarious to aerodynamics for cause of its rugosity. Soft icing is a combination of both with a mushroomy aspect on leading edges as its impact is also a combination of both previous

When Do Icing Conditions Form

Any cloud subjected to a temperature below 32° F may yield icing conditions. There is a risk of icing conditions when a plane is flying through a materialized humidity layer -like humidity shown in the form of rain, or clouds droplets- and when temperature is equal or below 33° F. The temperature further is lowered still through the aerodynamic encounter between the plane and humidity. Most favourable conditions to icing are found between 32° and 5° F. Such conditions are decreasing when temperature gets lower. Ascending currents however may transport humidity with such characteristics to higher altitudes and colder conditions -up to -40°F. Icing conditions may result either from statical, or dynamical condtions. At a low altitude, generally, small drops of fog or stratus are producing frost; at a medium altitude, altostratus and nimbostratus hold large drops as the most important icing occurs by 32° F or just below, in a 2,000 to 3,000-foot high layer. When layer has a height superior to 1,500ft, icing is not constant along the layer. Cumulus-type clouds, due to their ascendant currents, are holding large water drops, yielding ice as such conditions may reach to 30,000 to 40,000ft with temperature inferior to -40° F. Nature of weather fronts, seasons or terrain, on the other hand, may bring specific icing conditions, like icing areas found above mountain crests and upwind ones, up to 5,000ft above for example

Weather bulletins and forecasts are containing data concerning icing conditions. 'Trace' icing is a threat only when a plane is flying more than one hour in those conditions as such a icing is sublimating as it forms. 'Light' icing is a one accumulating slowly as it necessitates that the plane features anti-icing/deicing equipment as a non-equiped plane becomes threaten after one hour of flight in there. 'Moderate' icing is swiftly accumulating as plane non-equiped with anti-icing/deicing equipment must re-route immediately. 'Important' icing is accumulating so rapidly than even anti-icing/deicing equiped plane must re-route

Anti-Icing/Deicing Equipment

Planes, starting with advanced GA planes, comes equiped with anti-icing/deicing equipment. Anti-icing equipment, strictly, serves to prevent icing effects of impacting the plane with such features like pitot and static ports or stall detector heating, or protecting air intakes, propeller blades or windshield. Such features usually have to be preventively activated. Deicing equipement, as far as it is concerned, serves to get rid of icing which could settle in, as it consists generally into inflatable devices located unto wings and horizontal stabilizer leading edge. When inflating such devices evacuate ice or frost. Use procedures of anti-icing/deicing systems are contained into the plane POH. The more one goes beyond GA planes, up to airliners, the more and the longer a plane can withstand icing conditions

When a plane is not equiped with any anti-icing/deicing equipment, a pilot will have to closely monitor weather forecast along the route to draw a one which will avoid areas with possible icing conditions. When encountering such conditions during a flight, he will have to modify his altitude or re-route immediately. In terms of flight technique, one generally can remember the followings. In stratus-type clouds and even in any layer, or layer limit with icing conditions, just try to descent towards warmer air or to climb to colder one (where a temperature of about below 14° F). When encountering icing rain, the same as you will search for warmer air only (such weather conditions are a hint there is warmer air above). Just avoid any cumulus-looking clouds. When crossing a icing layer, fly with a slightly higher speed to counter any increased risk of stall. Avoid any sharp maneuver when icing formed due to a degradation of plane's aerodynamics, or, in such a case, increase your speed too for landing