Was told about this spell. It has the following description.
This spell grants the target the ability to swim through the air. Creatures with a swim speed can move through the air at that speed. Those without a swim speed must make Swim checks to move as normal. Still air is treated as calm water, light or moderate wind is treated as rough water, strong or severe wind is treated as stormy water, and stronger winds cannot be swum through. This spell does not grant the ability to breathe air to creatures that normally can’t.
As worded, would the target begin falling the moment they stop swimming in the air, or would they sink? If they sink, would they take the standard underwater penalties for melee attacks? I could see -2 ranged penalty for the initial square as well.
If they would just fall, I don't see the attack penalties, as it's probably a gamble to begin with, getting one attack at most.
The same would go if they fail the swim check by 5 or more. I guess it really comes down to whether the air around them is only treated like water when they're actively swimming, and it's treated like air the rest of the time, or if they essentially move through the air like water.
May I ask, why push back Fly until level 7? Why that number?
Anyway, I'd say use the rules for swimming. Which means that you need to make a swim check every round not to start sinking. In addition, you can only move if you succeed at the check.
It's a bit fuzzy what happens if you fail the check; do you also lose the action you might have used to move?
I'd run it like this: PC says whether he intends to move or not. Then he rolls a swim check.
If Move & Success: move using move/full action
If Move & Fail: fall a bit and lose indicated action
If No Move & Success: remain stationary, spend no action
If No Move & Fail: drop, spend no action
Now there's the question: what's your falling speed? While swimming, you don't sink all that rapidly. I'd say that failure just lowers your altitude by 10ft or so, with no risk of falling damage.
Note that unlike with Fly, when this spell ends or is dispelled, you don't get a free Feather Fall, so you can still plummet to your death.