Gentlemen (and Ladies, as applicable),
In my humble opinion (
), it's not a good idea to takeoff without a completely clean wing. My company's SOP is, very succinctly stated, "Make It Clean; Keep It Clean". There are too many pitfalls if you opt otherwise.
For example, years ago, an airplane crashed on takeoff due to icing on the wings. It was a cold, cold morning, and light snow had fallen during the night. When the crew arrived at the aircraft, the flight engineer (Yes, it was a long time ago!
) actually got a ladder and, with his hand, was able to brush the very dry snow off a section of the wing. It easily blew off into a fine powder. No problem...they all concluded it was safe to takeoff without being sprayed.
But, right after the snow-brushing analysis, they got their fuel. And, the fuel came from an underground tank...which, yes, you guessed it...was at a temperature well above freezing.
So, now, the warm fuel went into the wings, apparently partially melted the snow...which refroze...and, well, the rest is history.
A good, reliable rule to live by is to make it clean and keep it clean. That's the only sure way to know you're safe for takeoff. How you accomplish this is by following your company's SOPs. And, when in doubt, "DON'T" (is a good rule, too).
I've never had an engineer mind doing a tactile inspection of the wing to ensure the de-anti-icing fluid was still working. Yes, it's cold, snowing, etc., and the work conditions for these engineers are miserable. But, the consequences are simply too grave to do otherwise.
PantLoad