If you start your taxi (after dispatch) and the snow has already accumulated on the wing even in patches, it has "adhered" and you should be in violation of a hard rule if you dispatched that way.
The problem is the use of language … and I don’t necessarily limit that to the use of the English language. All languages present its users with some difficulty in expressing exactly what is meant. That’s why language is described as consisting of 3 parts: what is said, what is heard, and what is meant. Of course when snow is “blowing” across a surface it doesn’t “accumulate” on that surface. But I think anyone would be hard-pressed to say that simply because snow has “accumulated” on a surface, that it has also “adhered” to that surface.
There are a lot of the Canadian rules that are quite direct and to the point and would probably be preferred by most aviators – given the chance … but even then, the language our friends in Canada use can present the same sort of understanding or interpretation questions. For example the Canadian rule quoted as saying “…conditions are such that frost, ice or snow may reasonably be expected to adhere to the aircraft…” Then the question becomes, what is “reasonable?” Does “expected” mean that it is suspicioned to have adhered already, or will, within a short time in the future, begin to adhere? If it is expected in the future, what time frame would be acceptable – or – how short is short? Or, do we throw it all in the air and let the lawyers figure it out?
Using the word “accumulate” doesn’t necessarily solve these issues either. If any rule was changed to say takeoff must not be attempted when ice or snow has accumulated on the wing … then virtually any snow fall would prevent virtually any taxi time between “deicing” and “takeoff”. Anyone who has taxied from a gate to a runway for takeoff when snow was falling, can easily attest to the fact that “some” snow accumulated on the wings prior to taking off. If the parameters of such an accumulation cannot be clearly articulated and then adequately communicated, then, the conversation between the two Air Florida pilots becomes a lot more prophetic …
Captain: Right there is where the icing truck…they oughta have two of them, you pull right…
F/O: …right out
Captain: Like cattle … like cows right.
Captain: Right in between these things and then…
F.O: …get your position back
Captain: Now you're cleared for takeoff
F/O: Yeah and you taxi through … kinda like a car wash or something
Captain: Yeah
I know there are some airports who use precisely this method … and I would presume that there have been very few, if any, takeoff incidents attributed to ice or snow presence, accumulation, or adherence at those airports. The problem with this method is one of expense … both initial and maintenance … and then there is always going to be the environmentalists that would need to be satisfied with respect where the runoff would be captured and disposed of properly.
Ahhh … the simple life of an aviator …