• NC Software is proud to announce the release of APDL - Airline Pilot Logbook version 10.0. Click here to view APDL on the Apple App store and install now.

Visible Moisture

gear_guy

Well-known member
Joined
Jun 16, 2004
Posts
438
Total Time
6000+
Ok. Here's the question. What is your definition of visible moisture? I just got corrected in the sim because I did not use engine anti-ice.

Conditions were: Visibility of 3sm, temp of +5C, ceiling of about 3000', no precipitation reported. I was shooting a circling approach and had good visual on the runway.

Manufacturer recomendations are to use cowl anti-ice when temps are <+8C and in visible moisture.

I told them I thought the definition of visible moisture was <1sm visibility. Am I wrong? And do you know where to get the FAA or AIM definition?

Under their theory I could not be in a C-172 and fly that day even though it was VFR.
 

Amish RakeFight

Registered Loser
Joined
Dec 28, 2005
Posts
8,006
Total Time
.
Clouds - Fog - Rain - Snow - Mist.

With 3 miles of vis., you're operating in an environment of visible moisture.


.
 

Amish RakeFight

Registered Loser
Joined
Dec 28, 2005
Posts
8,006
Total Time
.
Oh yeah, you probably already know this but ambient temps drop around the inlet (due to camber - air acceleration) as the speed of the air increases and creates a drop in temperature.
 

gear_guy

Well-known member
Joined
Jun 16, 2004
Posts
438
Total Time
6000+
With 3 miles of vis., you're operating in an environment of visible moisture.


.
Is this opinion or fact? I have always been told <1sm. Where do you get this info and can you point me in that direction?
 

gear_guy

Well-known member
Joined
Jun 16, 2004
Posts
438
Total Time
6000+
Oh yeah, you probably already know this but ambient temps drop around the inlet (due to camber - air acceleration) as the speed of the air increases and creates a drop in temperature.
I agree with this too, but there has to be a limit. I am sure you don't shoot approaches in VMC with 10sm visibility with the anti-ice on. Or do you?
 

Fly91

Registered Pilot
Joined
Jul 31, 2008
Posts
635
Total Time
lots
Ok. Here's the question. What is your definition of visible moisture? I just got corrected in the sim because I did not use engine anti-ice.

Conditions were: Visibility of 3sm, temp of +5C, ceiling of about 3000', no precipitation reported. I was shooting a circling approach and had good visual on the runway.

Manufacturer recomendations are to use cowl anti-ice when temps are <+8C and in visible moisture.

I told them I thought the definition of visible moisture was <1sm visibility. Am I wrong? And do you know where to get the FAA or AIM definition?

Under their theory I could not be in a C-172 and fly that day even though it was VFR.

What was the humidity?
 
Last edited:

Fly91

Registered Pilot
Joined
Jul 31, 2008
Posts
635
Total Time
lots
If by that you mean temp/dewpoint spread, it was +5C/-1C

I would have had anti-icing "on" throughout approach and landing.

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

You're right about not being able to fly with a C-172, any general aviation aircraft without anti-ice protection couldn't fly.
 

gslippett

Member
Joined
Sep 14, 2005
Posts
7
Total Time
3000
"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

Well-known member
Joined
Jun 16, 2004
Posts
438
Total Time
6000+
"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

Registered Pilot
Joined
Jul 31, 2008
Posts
635
Total Time
lots
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

Well-known member
Joined
Jun 16, 2004
Posts
438
Total Time
6000+
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

Member
Joined
Sep 14, 2005
Posts
7
Total Time
3000
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

Registered Pilot
Joined
Jul 31, 2008
Posts
635
Total Time
lots
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

Registered Pilot
Joined
Jul 31, 2008
Posts
635
Total Time
lots
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

Well-known member
Joined
Jan 2, 2005
Posts
1,081
Total Time
13,000
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

Citation style...
Joined
Nov 11, 2003
Posts
5,311
Total Time
1500+
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.
 
Top