Comments Due on Definition of Known Icing

Comments are due today on an FAA draft letter of interpretation released April 3 on the meaning of the term “known icing conditions.” At press time, 82 comments had been filed, mainly by individuals. However, the National Air Transportation Association commented on the draft, saying, “Visible moisture and an aircraft surface temperature at or below zero degrees Celsius are two prerequisites for icing, but these two conditions do not guarantee ice will form. Therefore, icing can be determined only if there is a physical presence of ice.” The issue came to the fore after a June 2006 FAA regional counsel letter defined known icing as existing “when visible moisture or high relative humidity combines with temperatures near or below freezing.” Trade groups expressed concern about the definition, prompting the FAA to issue the draft interpretation, which said, “If the composite information indicates to a reasonable and prudent pilot that he or she will encounter visible moisture at freezing or near freezing temperatures…then known icing conditions likely exist.”