Then, I have the extra horsepower and FIKI system running and am ready to turn around.
Peter, good point. In most cases the best thing to do is to turn around to where you came from.
LeSving wrote:
That is one interpretation of it, but is very rare. The common type is ordinary rain falling down into cooler (subzero air) and freezes in the instant it hits something, the ground usually, but could also be an aircraft that have been flying in that cold air.
You are describing one common means whereby the droplets get supercooled.
JasonC wrote:
You are describing one common means whereby the droplets get supercooled.
LeSving is right they are two different things.
Supercooled rain (SLD) is below zero but still liquid.
But you can equally have warmer-than-freezing (ie. normal) rain, that becomes freezing rain (but never supercooled) as soon as it arrives at a sub-zero place, such as a cold airframe or the ground.
ortac wrote:
But you can equally have warmer-than-freezing (ie. normal) rain, that becomes freezing rain (but never supercooled) as soon as it arrives at a sub-zero place, such as a cold airframe or the ground.
Ortac you may be right but my understanding is that this typically still requires the droplets to be supercooled.
Yes; I would think that is implicit since both any falling water drops and an aircraft will stabilise to the ambient air temp within seconds (in the aircraft case, plus or minus the delta-T due to aerodynamic compression effects; these ultimately pretty well protect an aircraft doing more than about 300kt TAS).
So droplets at say +2C falling into air of say -2C will cool down to -2C within seconds and will thus become – by definition – supercooled.
From the NASA study:
Classical freezing rain develops when snow falls into a layer of above-freezing air (“warm nose”), melts to form rain, then subsequently falls into a sub-freezing layer of air to become supercooled (freezing) rain.
OK that makes sense. So I think the only freezing rain scenario where the rain would never be supercooled, would be the case of a cold-soaked airframe.
But that is impossible on a plane that is flying, because the airframe will stabilise to the ambient air temp almost instantly.
The scenario of air at +2C, rain at +2C, and the plane at -2C, would last only seconds (if that).
Aircraft skin has almost no thermal mass. What does have a bit of thermal mass is the fuel in the wings, and I have had cases where I descended from say -30C, rapidly, landed, and saw ice build up on the wings while sitting on the ground – all in VMC 
However, how many GA planes have the fuel in contact with the leading edge? The TB20 doesn’t – there is a gap of about 5cm.
I recall from my IR Met theory, Supercooled water droplets are mainly found in convective cumuliform clouds which allow the droplets to grow in size by collision. Freezing rain can occur where there is a temperature inversion or ahead of a warm front. Rain falls from a level where the temp is above 0 degs to a level where the temp is below 0 deg. If one can identify the ice formation is from freezing rain, generally this means there is warmer air above.
