Visible Moisture

[gslippett]

"In short, the FAA defines known ice as any visible moisture (cloud or limiting visibility due to moisture) with temperatures at or near freezing. If you go there in a non-known-ice-certified aircraft, you are in violation. Period."


This is from a letter written to a FSDO. Not directly answering your question I gather. Here is the link.
http://www.ifr-magazine.com/defining_known_ice_certification_faa_ifr.html

 

[gear_guy]

"In short, the FAA defines known ice as any visible moisture (cloud or limiting visibility due to moisture) with temperatures at or near freezing. If you go there in a non-known-ice-certified aircraft, you are in violation. Period."


This is from a letter written to a FSDO. Not directly answering your question I gather. Here is the link.
http://www.ifr-magazine.com/defining_known_ice_certification_faa_ifr.html

But it was VFR. The FAA defines VFR as greater than
3sm right? And you say the definition of visible moisture is any limiting visibility? In my opinion it was not limiting. It was 3sm, which again, is VFR.

 

[Fly91]

It boils down to the law when you live through an icing situation.

But what it should boil down to is:
High relative humidity or moisture you can actually see + 10c or less for reported ground temp = anti-ice "on". Better safe than sorry and you won't break the law.

If you're doing a circling approach, in 3sm visibility, there is moisture everywhere, you can actually see it just 3sm away, but your plane is also flying through it, you just can't see it. The FAA added "high relative humidity" to their legal interpretation of "known-icing" awhile ago.

C-172's and Warriors and a ton of other general aviation aircraft brweak the law every day in the cold months because of the "high relative humidity" addition to the law.

 

[gear_guy]

It boils down to the law when you live through an icing situation.

But what it should boil down to is:
High relative humidity or moisture you can actually see + 10c or less for reported ground temp = anti-ice "on". Better safe than sorry and you won't break the law.

If you're doing a circling approach, in 3sm visibility, there is moisture everywhere, you can actually see it just 3sm away, but your plane is also flying through it, you just can't see it. The FAA added "high relative humidity" to their legal interpretation of "known-icing" awhile ago.

C-172's and Warriors and a ton of other general aviation aircraft brweak the law every day in the cold months because of the "high relative humidity" addition to the law.

So then what does the FAA consider "high relative humidity" ?

 

[gslippett]

I agree....it's VFR 100% Heck, special VFR is 1sm, clear of clouds. What it seems is that they aren't speaking of whether it is VFR or not....Just emphasizing that it is a condition to accumulate ice one way or another. The fog, reducing visiblility to less than a mile from what I have seen is just a manufacturer recommendation to consider anti-ice on. Now, visibility can be reduced from particles in the air EX; smoke, temp inversion and then perhaps wouldn't be considered icing conditions. VISIBILITY REDUCED DUE TO HIGH HUMIDITY OR MOISTURE is their definition it appears.

 

[Fly91]

But it was VFR. The FAA defines VFR as greater than
3sm right? And you say the definition of visible moisture is any limiting visibility? In my opinion it was not limiting. It was 3sm, which again, is VFR.

VFR has nothing to do with icing conditions. VFR is 3sm OR greater. You can have icing conditions in what appears to be crystal clear weather. But 3sm is hardly good weather. At 3-1/4sm you wouldn't see a Boeing 747. That means there's alot of moisture that you're flying through.

 

[Fly91]

So then what does the FAA consider "high relative humidity" ?

Thats why I asked what the humidity was. The +5/-1 is a pretty close temp/DP spread, and that says why the visibility was 3sm. It was high humidity. So moisture was in the air, and you were flying through it, and it was cold.

I'll try to find what their definition of high humidity is, as far as exact numbers go. But I think they will probably leave that to us pilots using the temp/DP spread to figure out what we think is high relative humidity. WHY????? Because knowing how the FAA operates, they don't want to be liable for laying down strict numbers and then a pilot follows those numbers and still gets himself into icing trouble. Icing can happen when its not supposed to happen. Its just another grey area regulation. You can always ask the FAA for an "interpetation" of the reg.

Thats why I use anti-ice all the time, I probably use it more than anyone I know. I have my own rules. You can't die and you can't get busted or bitched at for using anti-ice when you don't need it, thats for sure.

 

[LJ45]

Thats why I asked what the humidity was. The +5/-1 is a pretty close temp/DP spread, and that says why the visibility was 3sm. It was high humidity. So moisture was in the air, and you were flying through it, and it was cold.

I'll try to find what their definition of high humidity is, as far as exact numbers go. But I think they will probably leave that to us pilots using the temp/DP spread to figure out what we think is high relative humidity. WHY????? Because knowing how the FAA operates, they don't want to be liable for laying down strict numbers and then a pilot follows those numbers and still gets himself into icing trouble. Icing can happen when its not supposed to happen. Its just another grey area regulation. You can always ask the FAA for an "interpetation" of the reg.

Thats why I use anti-ice all the time, I probably use it more than anyone I know. I have my own rules. You can't die and you can't get busted or bitched at for using anti-ice when you don't need it, thats for sure.

Lear says less than 1 mile in there AFM, which is approved, and you can't extrapolate the same temp/dew point from the surface and apply that at any other altitude.

 

[BoilerUP]

The FAA now deems any "area" that you are flying in that has high relative humidity is "known icing conditions."

That interpretation was rescinded back in late September.

 

[BoilerUP]

Given the circumstances, I would not have used EAI in that instance.

Cessna defines "icing conditions" in the Citation II AFM as temps between +10 degrees C and -30 degrees C, in precipitation or visible moisture (which includes visibilities <1sm).

Wouldn't hurt to use it in the given situation...but IMO wouldn't be necessary, either.