Most of what the average pilot thinks they understand about “known icing” is either confused or wrong – there is no prohibitive reg. under part 91 ( icing is an airframe limitation). Many misconceptions are implanted by well-meaning educators who are also mistaken or confused – sorry but let’s fix this now. I discover this ignorance continuously on flight tests, where applicants are supposed to understand this information (for good reason). I also witness confusion when discussing winter flights in the clouds with other pilots. It is not uncommon to see fear, misunderstanding and also incriminating accusations. Many well-meaning pilots condemn any flight in a “cold cloud” between September and June. A good place to start is with this Chief Council Opinion .
Flight into known ice is not directly referenced in part 91 and known icing conditions are only referenced in subpart F, which applies to large and turbine-powered multiengine airplanes and fractional ownership program aircraft. However, there are provisions in other subparts within part 91 that require a pilot to consider the consequences of flying in such conditions.
This is also an excellent “fire starter” for an exciting hangar discussion. Certainly, one sure way to create safety in aviation is always to just stay on the ground. But unfortunately, we have created a “boogeyman” that protects the innocents but also might keep every other pilot without a FIKI (flight into known icing) airplane from flying IFR (or even VFR) all winter long. This “cold cloud avoidance club” also points an accusing finger at any pilot who goes flying in the winter weather implying they are crazy and unsafe. This is an unfortunate situation that creates more heat than light so let’s dig in and find some middle ground.
Obviously, caution is a good thing, and I would be the first to admit there are definite, definable risks in winter IFR (as there are everywhere). But ignorance, denial, fear, and finger-pointing are not good strategies for successful aviation. As in any risk-management situation, we need to acquire definite skills, knowledge and training to fly safely in the winter weather. There are clouds that are safe and strategies to mitigate the icing risk. Please stay with me here and let’s poke the bear a little.
The legal prohibition – “operating limitation” – is in your POH or AFM, and you might have to do a little digging to find it. In addition to “approved” and “prohibited” operations for Flight Into Known Icing (FIKI), there are several levels of “semi-FIKI” aircraft, so the plot thickens. (Read your data carefully, you are legally bound to these restrictions). The FAA’s legal “gotcha” is actually CFR 91.13 prohibiting “careless and reckless operation” – which is included in every pilot violation or sanction. As always, you are PIC and you choose your conditions and tools to conduct aviation as you see fit; just do it legally and safely.
The definition of “known icing” has been changed numerous times by the FAA over the years. To find a solid legal definition you need to consult several good sources: Chief Counsel Letter of Interpretation, the Federal Register, the Advisory Circular and the AIM. Reading and understanding all of these in detail is the first step in flying safely in potentially icing weather; know the rules and cautions. (Also a good idea for flight tests)
“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 and that ice will adhere to the aircraft along the proposed route and altitude of flight, then known icing conditions likely exist.
Most recently – and what I hear often on most flight tests is – “known icing” is indicated (and flight prohibited) by “a current PIREP reporting icing.” For years this was regarded as the sure arbiter of “known icing,” and it certainly might be a time not to fly. Recently, the FAA, in the AIM, seems to even be backing off from this criterion as a definition or legal justification for pilot violation:
“Because of the variability in space and time of atmospheric conditions, the existence of a report of observed icing does not assure the presence or intensity of icing conditions at a later time, nor can a report of no icing assure the absence of icing conditions at a later time.”
The definition of “known icing” migrated from overly permissive to excessively restrictive in the late 1990s, limiting flight in any visible moisture below freezing. This draconian interpretation got the “cold cloud avoidance” started. As such, “known icing” became the boogeyman everywhere and always in winter clouds and the only legal IFR solution for non-FIKI pilots was “park it till June.” (Sorry for friends south of the equator). BTW, the ancient history of the “known icing” legal debate can be found here in AvWeb.
The current interpretation, issued in 2009, allows for pilot discretion in evaluating and choosing a “reasonable and prudent” course of action in most conditions: CFR 91.3 rules: (PIC). And if you examine most “textbook” icing accidents, you will see some really terrible conditions pilots failed to avoid and usually bad decisions made with partial information or “emotional planning tools.” In giving pilots discretion, the FAA is also providing enough rope to hang themselves. But “legal” does NOT mean “safe” and as in all aviation decisions, be comprehensive in your planning and cautious in your decisions.
Nearly one-quarter of all accidents due to airframe icing are caused by ice or frost that accumulated on the ground and wasn’t removed before takeoff, and carburetor or induction icing brings down three times as many airplanes as ice adhering to the skin. However, two-thirds of all fatal icing accidents are due to ice build-ups on the airframe in flight.
how does a safe pilot mitigate risk and fly IFR safely in the winter?
Parking the plane until June in the North is super safe, but totally ruins any utility and efficiency in aviation (cold cloud club). Launching without care or preparation to “get ‘r done” is a really bad expedient. Between these two polar forces of excessive caution vs. efficiency is where we negotiate safety in aviation. Flying on the east side of the Great Lakes for 40 years, I have seen pilots on both sides of this caution equation. I think the best answer is to prepare more carefully, fly with more caution (acknowledging the known hazards) and allow a greater margin of safety for escape in the event of surprises. Guidance for known ice approved operations is here in FAA AC 91.74B
So first, safety in potentially icing conditions requires a more comprehensive and careful preflight analysis, and there are amazing new tools especially from the NWS Forecast Icing Potential, FIP and Current Icing Potential: CIP CFR 91.103 (all available information). Knowing weather theory is also essential since this process is in motion. (Scott Dennsteadt’s excellent weather book is a great start for pilot education)
Second, obtain (and issue) PIREPS for any and all changes (especially for tops and temps.) PIREPS are the best real-time peer-to-peer information sharing system we currently have. During dynamic winter conditions where a few degrees of temperature make all the difference, information sharing is essential.
Lastly, always assure a safe escape route if you suddenly encounter icing, since it is impossible to forecast ice precisely and the consequences of unforecast icing are both terrifying and dangerous. Clear air below (but above the MEA) is best, but lateral diversions and big-picture awareness are essential for safety.
The FAA’s newest icing AC 91-74B is well written with lots of good information. And the NASA Glenn Research Website has a very good online training for pilots I highly recommend – knowledge, information and caution. Finding a savvy CFI with lots of experience in winter weather is your best educational resource (as always) since you need a mentor to explore any potentially-hazardous phenomenon safely. Stay warm and fly often!
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