Originally Posted by
Skyjob
Furthermore it is impossible to ignore the added weight by airframe icing on a large jet, which would not be taken into account in any performance calculations. (Imagine the weight of a few mm of airframe ice when you realise that the paint using standard 4-mil (0.1016-mm) paint thickness on a jumbo is already ~250kg!)
To be honest, the weight of the ice is not the concern, and I wouldn't rank it in the same category at all as the aerodynamic effects.
Firstly, all the weight will do is degrade the performance, a bit. Unless you get unlucky and lose an engine or have some other problem, the performance margins are usually going to be enough to absorb the extra mass.
What weight will not do, but ice on the wing's does directly do, is affect the aerodynamics. The wing will stall earlier, and likely differently to anything that it might have been designed to do. And the margin of the aero changes can be huge -30% in maximum lift isn't out of the range at all.
To illustrate, assuming a smallish airliner with about 1000sqft of area (wings, fuselage, everything) and as takeoff mass in the 30 tone range. Losing 30% of your lift is similar to suddenly weighing 30% more, so that would be 9 tonnes.
9 tonnes of ice, distributed over 1000sqft would be about 4 inches thick, if my maths is right. Snow can be substantially less dense than ice, so you're looking at multiple feet of snow. It's likely that an unaddressed accumulation would be somewhat smaller, perhaps a couple of inches of snow, max, or a thin layer of ice. Chances are, the effect of the mass of the contamination would be 1/10th of any aerodynamic effect.
Completely agree with your sentiment to keep it safe, but to be honest, mass isn't the main problem.