Ice formation

How ice formation is avoided on the wings of an airplane, while cruising at altitudes of 30000 feet or more where, the outside air temperature is extremely cold??

Ice normally will not form at temperatures below about -20 so high altitude ice is not a problem.
Thanks to the Air France accident we are hearing a few stories about high altitude ice, but it is very rare and appears to require weather conditions that we normally don’t see. Still lots to be learned.

John in Saudi

Thanks…but I am sure the air temperature at tat altitude wud be around -30F which is way more than required for ice to form…but i just want to know how is it avoided forming on the wings or body of an airplane cruising at tat altitude?

One of the major requirements for water ice to form is water. The air is relativity dry at higher altitudes so even though it’s cold enough for ice to form there’s no water for it to form from. See also porterjet’s posting above.

Thanks a ton for the info…

Partly true, but it’s not so much the lack of humidity but, because of temperature, any water in the atmosphere at that altitude will already be in solid form (ice crystals), hence there’s no “liquid water” to freeze on the airframe.

Any cirrus clouds that you see above 25000’ or so are comprised of ice crystals, not water vapor.

therefore, ice crystals will not create airframe icing because in order for ice to form two things are required; freezing temperatures and visible moisture, i.e. clouds or raing, a lower alt cloud is comprised of sub-freezing water therefore it hits your airframe and freezes to the cold surface. As far as “high alt” icing one thing comes to mind the movie “ironman” when he first is trying his flying suit he goes to an extremely high altitude and the whole thing iced over and he couldnt move. Thats highly innaccurate because like said, visible moisture, no ice will form in clear air. And when blasting through a cold cloud layer you may pick up some ice but as soon as youre above it in the sub freezing temps and in the sunshine clear sky the ice will sublimate off (change state from a solid to a gas)

hope that helps

phantomjet and ejericson - thanks for increasing my knowledge of icing at high altitudes. Very interesting - and said in a non-condescending way! Much appreciated.

I spend most of my day above FL400 and in the tropics you find clouds at and above FL400.
the reason the ice crystals don’t stick to the aircraft is because the aircraft is supercooled. place a piece of aluminum at -60F and it becomes pretty cold.

Also, and I know that this is not the norm. last months after accidentally penetrating a thunderstorm at FL450 I encountered rain. The drops were the size of a silver dollars.

Ice formation is a strange thing. I use to run a C-206 between Gelena AK (PAGA) and Huslia AK (PAHL) 3 days a week on a mail run. At the start of winter I encountered icing while NOT in visible moisture. It was mixed ice. it’d get pretty bad at times. I’ve actually used the control lock to scrape ice from the windscreen- IN FLIGHT.

:smiley: Let’s not bring any terms like “supercooled” or “droplets” into the discussion or else none of us will have any good answers I’m afraid…