What is known icing?


So how cold is cold enough to fly in the clouds? Does the FAA define it?

This is the METAR for the airport I fly out of. I know that there is a SR20 and Piper Warrior up flying.

KXXX 291553Z 34019G26KT 1SM -SN BLSN BKN016 OVC039 M17/M19 A2997

So there are clouds = visible moisture
It is below freezing = icing condition

visible moisture + icing conditions doesn’t this = known icing conditions or forecast icing conditions?

Why is there no AIRMET for icing? How can these airplanes be flying? They don’t have ice protection. Why doesn’t the FAA define this?


you need to go read an article in IFR Magazine about this - AOPA also has the letter from the FAA and their response on their website

aopa.org/whatsnew/newsitems/ … icing.html

they complain about the idiot who wrote the letter . . . the definition apparently is now ‘high humidity’ whatever that means.

The AIM states that visible moisture and below freezing temps create the potential for icing. In the ‘real world’ where we fly, it is much more complicated than that. I have flown at night IFR in a blinding snowfall and not picked up even a flake of ice, and likewise flown into a thin cloud I could see though and picked up a quick 1/4" of rime.

At temps that far below freezing - Minus 17C is 1F - the chance of snow sticking to an air frame that cold is fairly low. Take that same airframe, and have it be at 0, 1, 2 or 3C and fly it through rain or snow, and it’ll stick fast.

Drive a car through moderate snow at 32F, the snow will stick everywhere and the wiper will get coated. Drive that same car through snow at 15F and it not stick to anything. Same concept.

That being said, you have one mile visibility in snow and blowing snow and there are small airplanes flying around? Perhaps on an instrument approach, but just flying in the pattern? The runway must be somewhere between what 33 and 35 with winds like that as well? Just cause someone is doing it does not make it safe …


The AIM states:

Known Icing Conditions
Atmospheric conditions in which the formation of ice is observed or detected in flight.

AIM 7-1-23 Table 7-1-8
They could end there with a big fat period, but they add:

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.

From my point of view, I’ve always used the AIM definition when flying light airplanes. I don’t think that an airmet for icing is “known icing” either, any more than an airmet for thunderstorms means that you can’t fly either. Under the AIM definition, only PIREPs or your own observation is “known”.
I’ve heard that the FAA is going to back down a little bit on this issue and wait and see how the chellenges from AOPA and other groups pan out.


I am told that a certain airplane manufacturer, which has anti-icing but does not have certification for known icing on their planes, has told people that the only known icing conditions are those reported by another pilot and even that is only for a specific place and time. According to them, clouds and freezing temps and/or a forecast of icing does not constitute known icing. It should be noted that the FAA does not necessarily agree with this position.

For the purposes of flight planning and safety, I would say clouds and temps around (17 - 37 degrees F) freezing are a signal that you may encounter icing conditions. For legal purposes, it is possible that only a PIREP constitutes known icing, but ask yourself how far you want to push the envelop. The legal definition will probably only matter if something bad happens.

The FAA has several good resources about icing, including:


discussions.flightaware.com/view … 31&start=0

It’s amazing what kind of info can be found with a leeeeetle scrolling down… :unamused:


Generally, and it will depend on which source you read, ice will develop between +5 through -20.