Clouds and Building Ice

[Please Hire Me]

Forgive me for what might be an insanely stupid question. I was in a little debate with my fiance (also a pilot ) and she was telling me that you will ALWAYS build up icing in the clouds, because it's "visible moisture." I say no, because if it's cold enough, the so-called "moisture" will be frozen.

SO... am I right? I feel ridiculous asking, but she often proves me wrong. I hear you dont have to worry about icing in the clouds unless you are withing 10 degrees of freezing temps.

Your input...?

 

[CaptBuzzard]

You won't always collect ice in the clouds. The temp has to be right. If you are well below the freezing level, then you most likely won't build up ice. If you are withing the freezing levels, then you may get ice. I have seen ice on the plane I fly anywhere from +2 C to -25 C. Those are the temps that I generally fly in this time of the year. I have read in an icing book that there has been icing reported at -50 C which at that point the air should be too cold for ice to form, but anything can happen.

 

[Sphincter Boy]

You can get such a thing as impact icing, but I've never heard of that bring anyone down. The minus 50 temp icing that you referred to occurs with SLD conditions.

 

[JetPilot500]

Supercooled water droplets are droplets of water that are below freezing but still in liquid form. Ice build up occurs when supercooled water droplets stick to the airplane. As these "water" droplets strike the airplane, they immediately change to the solid form, ice, if the surface is below freezing. When frozen droplets or ice crystals, strike the surface, they just bounce off. That is why icing typically occurs at temps from around 0°C and -20°C. Below -20°C, the droplets are pretty much completely frozen and will not stick. This is why, you will not usually have to worry about icing in Cirrus clouds.

Yes, icing can occur at any temp below freezing, but it is rare. One of those instances where you can get ice at very cold temps would be during convective activity. Lets say you are Flying at FL350 with lots of convective activity in the area and the OAT is -60°. Updrafts can drive water droplets into the high (and cold) atmostphere where they do not have time to completely freeze...until they strike your airplane surfaces.

But, generally, in stable conditions you will not get icing when the temperature is below -20°C.

Hope this helps,
JetPilot500

 

[bigsky]

as always there are exceptions such as convective activity, but I would say for the most part that clouds above fl280 are mostly tiny ice crystals and usually do not require any anti-ice. I know some airlines use -40 as a cut off point as whether or not to use engine anti-ice

 

[mckpickle]

ALWAYS.........no not always. But generally if the temp is with in a couple degrees of freezing and you have visible moisture than you will. However.............snow is already frozen so what you usually get, as stated above, is impact ice. IE the snow impacts the leading edge and builds a little. Snow is good to fly in because it's already frozen.

Now USUALLY at temps -10c and below there isnt much moisture because the air is too cold to hold said moisture, but i've seen severe ice at temps of -20. Hope it helps.


Oh And why the he11 are you going to marry a pilot? Are you nuts?

 

[tarp]

I think you have her with the ALWAYS comment but she is more right than you are with +/-10 degrees of freezing.

I've flown the Dork Jet and it has some pretty good numbers that coincide with what "generally" happens out there.

Temp < +10C and visible moisture - Be ready for ice.
Temp < -25C - Boots must be switched from Fast to Slow
Temp < -40C - Boots off.

Basically, from +10C to -25C, be ready for normal accretion of ice.

From -25C to -40C, the Dork folks felt that there wasn't that much ice that would stick to the airplane and the boots sure don't like expanding and contracting at those temps. i.e. icing possible but that really is getting cold.

From -40C and colder, well first what the heck are we doing trying to operate an airplane there, but the engineers doubted much ice and definitely didn't want us to try and stretch boots at that temp.

 

[eriknorth]

Check this out:

Aircraft Icing Handbook

 

[Please Hire Me]

Check this out:

Aircraft Icing Handbook

Great link! Thanks!!!

 

[freeflyer14]

What exactly is considered "known icing"? Is an airmet for ice considered known icing? Pilot reports of ice? How long would a pilot reporting ice constitute known icing?