CRITICAL SURFACE CONTAMINATION


An accumulation of frost, snow or ice on the wings or other horizontal surfaces will substantially alter the lifting characteristics of the airfoil. Even a very light layer of frost spoils the smooth flow of air over the airfoil by separating the vital boundary layer air, producing an increase in stall speed and a decrease in stall angle of attack. Incredibly, just a few millimeters of ice will increase the stall speed by as much as 20%. Any substantial accumulation of snow or ice, drastically disrupts the airflow over the wing. This will decrease the amount of lift the wing can produce, making flight difficult or impossible.


There are a number of major factors that contribute to critical surface contamination, and a knowledgeable pilot will recognize them as indicators of icing conditions.


Ambient temperature provides a good indication of the potential for icing conditions.


Aircraft surface temperature indicates the susceptibility of the aircraft to icing. Aircraft surface temperature is affected by solar radiation. An aircraft will have a warmer surface temperature on a sunny day than on an overcast day with identical ambient temperatures. When the fuel in a wing fuel tank is very cold, the cold fuel in the tanks can so chill the aluminum wing surface so that moisture in humid air or rain will turn to frost or ice over the fuel tank.


Be alert to the conditions that cause icing even before going out to your aircraft. Get a thorough weather briefing and the most up-to-date forecast so that you are aware of temperatures and precipitation at your stops and enroute.


Examine your aircraft very carefully prior to flight. Use your eyes and hands to examine the surfaces to ensure that your aircraft is “clean” before departing on a flight. Have the aircraft de- iced by ground crews if there is any contamination. Be sure that the de-icing fluid is used evenly on both sides of the aircraft and on the under, as well as the upper surfaces. Use wing covers to protect your aircraft when it is parked.


7 Surface Contamination


Surface Contamination 7


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