You'd need wings, flight feathers, a specialized light bone structure, specialized flow-through design heart and lungs, specialized tail, specialized general balance parameters etc.
For starters, every one of these things would be antifunctional until the day on which the whole thing came together, so that the chances of evolving any of these things by any process resembling evolution (mutations plus selection) would amount to an infinitessimal, i.e. one divided by some gigantic number.
In probability theory, to compute the probability of two things happening at once, you multiply the probabilities together. That says that the likelihood of all these things ever happening, best case, is ten or twelve such infinitessimals multiplied together, i.e. a tenth or twelth-order infinitessimal. The whole history of the universe isn't long enough for that to happen once.
All of that was the best case. In real life, it's even worse than that. In real life, natural selection could not plausibly select for hoped-for functionality, which is what would be required in order to evolve flight feathers on something which could not fly apriori. In real life, all you'd ever get would some sort of a random walk around some starting point, rather than the unidircetional march towards a future requirement which evolution requires.
And the real killer, i.e. the thing which simply kills evolutionism dead, is the following consideration: In real life, assuming you were to somehow miraculously evolve the first feature you'd need to become a flying bird, then by the time another 10,000 generations rolled around and you evolved the second such reature, the first, having been disfunctional/antifunctional all the while, would have DE-EVOLVED and either disappeared altogether or become vestigial.
Birds, of course, are simply the easiest case to visualize. Every other complex creature which ever walked the Earth involves the same kind of zero-probability event sequence holding good.
Basically, if a theory requires one or two probabilistic miracles or zero-probability events in the entire history of the world, you might could still listen. But evolution just stands everything we know about probability on its head.
<];^)
You have proven that flying squirrels do not exist.
And as Dial's experiments show, when a juvenile is trying to evade a predator this way, the aid of even a partially formed wing can mean the difference between life and death.
From your post:
I'll say it again: to be a flying bird, you'll need a baker's dozen highly specialized systems, any one of which would be anti-functional and a severe impediment until the day it all arrived.
Either you did not read the article, or you simply give knee-jerk responses whenever the subject of creation vs. evolution comes up. Pavlov would've have loved you (and gore3000, but that's another story).