frost on the wing

The other day I went flying, pretty close to the shortest day of the year, to preserve night currency. I took advantage of a day that wasn't brutally cold - in fact it was above freezing, so I didn't need preheat or thermal underwear. It was good to get in the air after several months of not flying hardly at all (we had the longest, most beautiful fall but I was stuck indoors doing two shows at the same time). I had to taxi over a bit of an ice berm in front of the wheels, but it wasn't a problem, and the pavement was wet from the melting ice (we had several inches of ice storm a week or so ago which is still around).

By the time I got in the air, I was happy and all was well with the world. After doing some night full stop landings, I followed I-84 up to Beacon and back just to "go somewhere" and then came home. By now temperatures were just below freezing, but it was clear and so I didn't give it much consideration.

Landed without incident, braking was good (and was also reported good by aircraft before me), and I taxiied to the ramp, a relatively unfamiliar part of the airport since we moved the airplanes. The airplane seemed to be sliding a bit, as if there was ice on the pavement. Well, of course there was; the wet pavement had frozen in the interim. I was afraid of that, and this meant that putting the plane away would not be as easy as taking it out. After a struggle I did manage to get it pushed back over the ice berms (pulling up on the wing while pushing back helped, as did pulling with the tiedown ropes when I got close enough). But when I was pretty much done, I noticed there was frost on the wings, which hadn't been there before.

Which got me thinking - maybe the FAA isn't so crazy after all. If frost can form while the plane is just sitting there, why could it not form while the plane is flying? (yeah, there's some frictional heating, but we could lower the temp a bit more, no?) And if frost isn't such a good thing to have on takeoff, it's probably not so good in flight either.

Any thoughts? Have you seen this before?

Jose
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