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Why does ice sometimes form on the top of a wing and not on the leading edge?

Off_Field wrote:

Could it be due to a pressure change perhaps, a drop may cool it enough to form ice?

I would go with this. Simplest explanation. The point indicated is (or is close to) the point of lowest air pressure.

EGLM & EGTN

Ibra wrote:

I am not sure if it is fuel related, my guess 30min after takeoff fuel temps and wing temps will match OAT quickly (otherwise happy to warm up wing & fuel to 40 deg in a heated hangar and use it as de-ice in my non-FIKI aircraft )

My experience with ice from cold fuel is that it happens after long flight at altitude and subsequent descent through clouds.

Cobalt seems plausible were large supercooled droplets did hit separation turbulence and suddenly freeze, sort of shock induced freezing of supercooled water, the question why did not freeze when impacting the leading edge? my guess this has a thermal explanation: TKS was effective to heat them up just about not to freeze at leading edge but not very effective to raise their temperature so high to avoid re-freezing again on the back of the wing?

Being fresh after ATPL theory, I still have echoes in my head about “large supercooled droplets” freezing aft of leading edge.

LPFR, Poland

It is the pressure change!

Ice needs visible moisture to form (that is condensed water). Reduction in pressure increases relative humidity. If you have a relative humidity close to 100% it might happen that due to the reduced pressure on top of the wing humidity hits100% and condenses in that area. At temperatures in the freezing range this condensed water can form ice on the wing.
It’s a similar effect when we see stripes of condensed water at trailing edges of flaps in final approach.

Germany

This topic is explained here: https://scandlearn.com/course/winter-operations-and-surface-contamination-training
Section Certification standards, slides from 34.

LPFR, Poland
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