Visible Moisture

[gear_guy]

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]

Clouds - Fog - Rain - Snow - Mist.

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


.

 

[Amish RakeFight]

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.

 

[THE Flying Ace]

Simuflite has said vis less than 1mi, rain, snow, etc.

 

[gear_guy]

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]

Simuflite has said vis less than 1mi, rain, snow, etc.

That's what I always heard too. But I need a document to point to.

 

[gear_guy]

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]

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?

 

[gear_guy]

What was the humidity?

If by that you mean temp/dewpoint spread, it was +5C/-1C

 

[Fly91]

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]

"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.