We picked up rime ice.

[pierre smith]

IFR in IMC to Beaufort, S.C. yesterday, we picked up rime ice in the clouds, transitioning from 4,000' to 7,000'. It was 22 deg OAT, so I figured that any moisture would be frozen.....not so, it froze on the windshield and leading edges. We kept an eye on it and stayed above the clouds, noting the loss of 12 MPH..probably the landing gear and tailfeathers were also iced up.

Do super-cooled droplets stay liquid that cold? Apparently so.

Best,

[humptybump]

Pierre, once on top and no longer adding to the problem, did the ice sublimate or did it stay for most of the flight?

[n5lp]

Originally Posted by pierre smith

IFR in IMC to Beaufort, S.C. yesterday, we picked up rime ice in the clouds, transitioning from 4,000' to 7,000'. It was 22 deg OAT, so I figured that any moisture would be frozen.....not so,..

I guess that must be a 22 F. Prime icing temperature there and it can occur down below 0 F.

[rzbill]

Yeah Pierre,
The weather north of you in NC yesterday was just good enough that I could go VFR and stay out of the clouds for just the reason you state. It was snowing at surface but I still didn't trust the clouds.

[ILikePike]

I picked up some ice last week in the bonanza on a trip to HSV. It was 26 deg F in a layer from 4-7000, I got on top in the clear and the ice did sublimate. I was surprised that the moisture was not frozen. Being from the southeast, I am afraid of ice and try my best to avoid it. Therefore, I have little experience in dealing with it.

[pierre smith]

Originally Posted by humptybump

Pierre, once on top and no longer adding to the problem, did the ice sublimate or did it stay for most of the flight?

No, it stayed on, about 3/8" thick and about covered the leading edge for a couple of inches. We descended quickly, to avoid picking up more ice and it came off kinda quickly once the temps got around 36 F.

Best,

[SmilingJack]

I've picked up ice I a very wide range of temps at lower altitudes. Most all aircraft I have flown have the limitation of anytime TAT is 10c or below anti-ice systems must be selected on.

Just the other day at +13 I didn't select anti-ice and experienced what you did Pierre, ICE! And guess what happens next? The temp went up 1 degree and the airplane started yelling at me because it was to hot for anti-ice

The one aircraft I remember was a Challenger where they indicated in the AFM at altitudes above FL210(i think that was the altitude...give or take a thousand ft) anti ice was not needed due to the ice being crystals. While other aircraft don't state that and therefore must be used.

I know I am not talking RV's, but your experience is a great one to pass along to all of us while flying without anti-ice systems.

Flying in icing, departing in areas of frost...these are great topics to review and respect! Great Post!

[bkthomps]

Originally Posted by pierre smith

Do super-cooled droplets stay liquid that cold? Apparently so.

Best,

22F is not supercooled, and the way I understand it, if you saw it on the leading edge of these airfoils, your tail most likely had a pretty decent layer growing, search around and there is an inflight portrait of someone with quite a bit of ice on his tail

[bruceg]

This comes from AC 00-6A, Aviation Weather

SUPERCOOLED WATER
Water droplets colder than 0 C are
supercooled. When they strike an exposed object,
the impact induces freezing. Impact freezing of
supercooled water can result in aircraft icing.
Supercooled water drops very often are in abundance
in clouds at temperatures between 0 C and
-15 C with decreasing amounts at colder temperatures.
Usually, at temperatures colder than
-15 C, sublimation is prevalent; and clouds and
fog may be mostly ice crystals with a lesser amount
of supercooled water. However, strong vertical
currents may carry supercooled water to great
heights where temperatures are much colder than
-15 C. Supercooled water has been observed at
temperatures colder than -40 C.

[bkthomps]

Originally Posted by bruceg

This comes from AC 00-6A, Aviation Weather

SUPERCOOLED WATER
Water droplets colder than 0 C are
supercooled. When they strike an exposed object,
the impact induces freezing. Impact freezing of
supercooled water can result in aircraft icing.
Supercooled water drops very often are in abundance
in clouds at temperatures between 0 C and
-15 C with decreasing amounts at colder temperatures.
Usually, at temperatures colder than
-15 C, sublimation is prevalent; and clouds and
fog may be mostly ice crystals with a lesser amount
of supercooled water. However, strong vertical
currents may carry supercooled water to great
heights where temperatures are much colder than
-15 C. Supercooled water has been observed at
temperatures colder than -40 C.

interesting, i was thinking supercooled was defined as extremely negative temperatures, never thought about the technical definition, learn something everyday!