Not all clouds contain icing even in the danger temp range from around 10F to 35F. But I was always real nervous in a light plane in IMC much below about 40F. I never operated in serious arctic conditions where the temps were reliably below 0F. I would not be too nervous once it got that cold.
I recall one lightplane flight from Las Vegas to Los Angeles in winter. There was layered stratus from about 2000AGL up to well above my cruising altitude of 8000MSL. I went pretty much the whole way in IMC with a careful lookout at the wings. For a few seconds at one point I was building frost and was just formulating my escape plan when it stopped accumulating. Over the next 5 minutes it sublimated away. The other 2-ish hours of IMC flight had no ice. The clouds looked the same the whole time.
Bottom line there: icing is capricious.
Going to your questions:
- As we know, in general temps lapse about 2C/3+F per 1000 feet with increasing altitude. But not always, and winter seems to have more exceptions than summer.
For example, freezing rain is caused by snow or ice pellets formed at high altitude then falling into a layer of above-freezing air from, say, 5000 down to 1000 AGL, with colder air & ground below. Falling through the warmer air layer the snow heats just enough to liquefy then falls into freezing air again, supercools, then hits the ground and freezes on impact. Or on the airplane if there’s one stupid enough to be flying there. Hint: we avoid FZRA about as much as we avoid TSRA+; that stuff will kill a jet, much less a Cessna.
It’s pretty common that the base of the clouds is right at that lower freezing level = the base of the warmer air. This is true whether there’s any precipitation or not.
In the accident case it’s plausible the clouds were warmer than 32F if they were as low as you say, and he was only a little ways into them and it was roughly 32F at ground level. No guarantees, but it’s plausible.
You can get pretty evil icing in clouds just above 32F too. That’s the way to get clear (i.e. non-rime) icing. The air & water vapor & any condensed water are all sitting there at, say, 34F. Then you blast through and your wings & fuselage drop the pressure and the stuff in contact with your surfaces freezes in the reduced pressure.
- No clue. Might be darn tough on an uber smooth shiny white surface.
3a: How to respond to icing:
Good academics and a good weather briefing can alert the pilot to the conditions where ice is likely and the vital importance of having an escape plan and of avoiding *reported *conditions beyond the airplane’s capability. The problem is ice is capricious and half the country wouldn’t fly at all in winter if they avoided all forecast icing, not just all reported icing. OTOH, if you’re the first lightplane on V123 today since everybody else is smart enough to stay home, you’ll be the one giving that first pirep in severe icing.
The standard remedy to encountered icing is to climb if possible. The goal is to get up to where the temp is below about 10F. Below that temp ice won’t form on the aircraft; any macroscopic water’s already frozen & bounces off instead. As well, climbing may get you to VMC. That’s remedy is often not useful for light planes with low rates of climb and low service ceilings. Knowing the forecast or reported cloud tops in your area is useful info. If they’re high, like they were on my flight to Los Angeles, you know to not waste time trying to climb to VMC. And a look at your OAT vs. altitude available up to your service ceiling will finish the question of whether climbing is likely to help.
Gotcha: The top 500 feet of a cloud before you get up into VMC is the area most likely to have rime ice. Which generally creates the fastest performance degradation of a light plane. So about the time you can see daylight above through the thinning mist & things are looking promising is when Nature drops one more joker on your pile. Maybe you do climb out of it and maybe you suddenly can’t.
Descending works too, but real quickly you get into MEA versus cloud height problems. If you can’t get down to VMC you need to descend in IMC to find a temp above about 35F. Which may not exist above ground level where you are.
Typically the danger temp range is about 12 degrees C = about 6000 feet thick. So knowing whether you’re cruising at the top, middle, or bottom of that range is need to know info before you wander into an ice patch. Likewise whether there’s warm air (or any air) between the cloud bases and the MEA.
Last solution is turn tail & run the other way. Since icing is patchy, you can expect to get back out of it shortly after finishing your 180 turn. The hard part is admitting you’re not getting to the destination today.
3b. How to fly with ice on the aircraft:
They teach us you can’t make any really useful predictions about the consequences of ice on the airframe. Stability is worse, stall speeds are higher, handling & control is degraded, both natural and artificial stall warnings may not function. IOW, you’re a test pilot of a new & really crappy design; Good luck, Chuck.
They also say it doesn’t take much. Typical light frost on a wing leading edge can raise stall speeds & reduce lift by 50% each.
If I had to land a lightplane with a load of ice I’d land no-flap and touchdown not too far below cruise speed with very little flare. No slower than halfway between cruise speed and placard flaps up stall speed. If that’s above gear lowering limit speed I’d drop the gear anyhow. And use no more than 10 degrees of bank inflight.
I’d far rather run off the end of a runway at 50 kts than fall out of an approach from 100 or 1000 feet.