AirRabbit
Of course it would be somewhat foolish to completely dismiss your recommendation – but, at the same time, if the wing must be absolutely clear of any accumulation of snow (to see that there is absolutely no ice adhering) wouldn’t that effectively eliminate any takeoff during a snow shower? Is that acceptable to the myriad of operations that take place daily in locations where snow appears during winter operations?
It's pretty simple. To begin the T/O roll, you must have a clean wing, critical surfaces, etc. that are free of frost, ice, or snow. "Clean" can include anti-ice fluid that hasn't failed/reached its saturation point. If its not wet and glossy but turned opaque, and especially if there's snow present on the fluid surface, the solution has lost the ability to melt frozen precip and absorb/suspend/depress the freezing point of the water. Unless other procedures have been approved in the Ops Specs, the general rule for U.S. air carriers (121.629) if HOT has been exceeded there must be pre-takeoff contamination check accomplished within 5 mins before T/O, and it must be done from outside the aircraft. If the pilot has miscalculated the precip type/intensity or other variables came into play (rapidly chancing temp/wind/jet blast) that cause visual indications the fluid has failed within the HOT, the pre-takeoff contamination check from outside the aircraft within 5 mins must still be done. When the fluid has become saturated, it's impossible for a pilot inside the aircraft to visually ascertain if there is re-freezing/adhering to the critical surfaces underneath the fluid. There are no "representative surfaces" for the contamination check, only the real ones. Since the manufacturers of fluids do not give a holdover times for heavy snow conditions, it did use to cease t/o operations because it threw Type 4 HOT tables out of whack, but now it's allowed if it's applied at 100% strength and a "definitive fluid failure determination" made within 5 minutes of takeoff.
In any case, no matter how you're trying to parse it, if it's not a dry, feathering snow readily sliding off a cold-soaked wing but is accumulating on it instead, then it must be adhering somewhere...you certainly can't make a definitive determination that it isn't. If it has accumulated on the surface of de/anti-ice fluid, the fluid has failed. In either case, this "accumulation" of snow it doesn't meet the criteria "free of". It's contaminated. Period.
some 30 years ago – we used to think that asbestos was a good insulator – we used to think that cigarette smoking was a pleasant past-time – we used to think that 8 miles-per-gallon was reasonable mileage for a car – we used to think it appropriate for parents to send their kids to the park to play all by themselves – we used to think that taking off with a small amount of snow accumulation on a wing that had been recently deiced was OK
30 years ago was 1982. There had already been 2 oil crises, everyone knew asbestos and smoking were bad for you, and it was already loud and clear that frost, ice, or snow on the wings during takeoff could kill you. At least in my neck of the woods where it was lousy with all 3. It was certainly widely disseminated aviation knowledge, but I realize that doesn't preclude pilots out there making up their own theories that become culture within fenced-off circles, those within convincing themselves it's routine thinking; "This type of wing handles it", "That'll slide off I've seen it before". There's always pilots that theorize about CBs too...the "Oh that's just rain" type who once flew through the red blob of a dying airmass baby in Florida who then supposes that's what he'll find inside a steady-state Level 6 over Kansas. The same mentality that screws around with snow on the wings and red on the radar stands a good chance of pushing their own metal into the smoking hole.