Defining "Known" in "Known Icing Conditions"

By Gene Benson

It's finally here! After very many years of ambiguity, the FAA has decided on the meaning of "known icing conditions". If you are a pilot who has wrestled with this question you might be shocked by the answer. Before we reveal what the FAA has to say, let's look at some background.

Here in the northeastern part of the United States there are three facts that are as unalterable as the laws of aerodynamics and the high tax rates. They are as follows: (1) It will get cold between the months of October and May. (2) There will frequently be clouds at the altitudes where general aviation airplanes fly. and (3) Structural icing can occur when an airplane flies through visible moisture in temperatures near or below freezing.

Ever since I first started training for my instrument rating in the early 1970s I've been hearing that it is not legal to fly in "known icing conditions" unless the airplane has been certified for flight in such conditions.  Obviously it's neither smart nor legal to launch off into conditions where pilots have been frantically issuing PIREPs for structural icing. It's also not smart, but up to now, not necessarily illegal, to embark on an instrument flight in an airplane not equipped to handle ice when the temperature at altitude will be below freezing and most of the flight will be in the clouds.

So what is a "known Icing condition"? I've been asked that question hundreds of times by my students. FAR Part 1 is titled, "Definitions and Abbreviations" so it certainly contains a definition of something as frequently discussed as "known icing".  Wrong!  "Known icing conditions" joins many other regulatory terms such as "congested area" that are not clearly defined as a part of the Federal Aviation Regulations.

Anything not defined is open to interpretation. Some pilots have considered icing to be "known" whenever their airplane will pass through visible moisture at a temperature near or below freezing. Others have not considered icing to be "known" unless ice was actually accumulating on their airplane. The FAA has rarely pressed the issue unless an accident or incident occurred or the flow of air traffic was seriously disrupted by a pilot declaring an emergency due to structural ice.

But the question has lingered. What exactly is a "known icing condition"? Recently, the FAA was confronted by a demand for a clarification. Time will tell whether or not safety and/or the furtherance of general aviation was well served by this action.

So here it is straight from the FAA legal counsel: "Reduced to basic terms, known icing conditions exist when visible moisture or high relative humidity combines with temperatures near or below freezing. Since clouds are a form of visible moisture, flying through clouds at an altitude that is near or below freezing would constitute flight into known icing conditions. Another factor to consider, as a practical matter, is the temperature of the aircraft exterior. When the air temperature is close to but above freezing, any part of an aircraft exterior that is below freezing may cause water droplets to freeze and ice to accumulate. When the air temperature is below freezing, any part of an aircraft exterior that is above freezing (e.g., engine cowling) may cause snow or ice crystals to melt, refreeze, and further accumulate as ice. The Federal Aviation Regulations do not allow for experimentation. Flight into known
icing conditions when the airplane flight manual or pilot operating handbook prohibits such flight would constitute a violation whether the aircraft accretes ice or not."

Click here to see the actual FAA interpretation letter.

So now it's very clear. If a pilot flies through a cloud, in an airplane not certified for flight into known icing conditions, when the temperature is near or below freezing, a violation of Federal Aviation Regulations has occurred. Effectively this eliminates most IFR operations in small general aviation airplanes in the northern part of the United States from early fall to mid spring.

Will this prevent pilots from flying in dangerous icing conditions and prevent accidents? Will the FAA now position inspectors at airports to write violations against pilots who arrive IFR on cloudy days during the winter? Will pilots engage in "scud running" to avoid flying IFR in cold clouds? Will the FAA largely ignore this legal interpretation and continue with the status quo? I don't know the answer. What do you think? How will this affect your flying? Please send me your comments at gene@genebenson.com or use the secure comment form by clicking here.

Copyright © 2006 Gene Benson