I'd say that you could use Spring Attack while flying. It simply allows you to move before and after your attack.
Flyby Attack is SLIGHTLY different in that it allows you to take a partial action during your move. Technically, a flying wizard could do this to cast a spell, such as fly in range of the spell, cast, and then fly back out of range.
I'm not sure how these two abilities would work if you were trying to use both. I'm guessing that if you used Flyby attack to make a melee attack, it would act almost the same as spring attack. The only difference is that part of your move could be a dive action, so you can dive, which is an attack, then make ANOTHER attack, then fly away.
I'm confused about what the heck that text for Flyby attack in the SRD means when it says "The creature cannot take a second move action during a round when it makes a flyby attack." Eh? I'm guessing this is specifying that you have to take your partial action DURING the move, and that you can't take one move action, a partial action, and then ANOTHER move action. You have to take your partial action DURING the ONE move action.
Why this matters, I'm not sure.