Ascalaphus has the correct answer by the book answer, but I find most GMs completely ignore flying skill check rules unless an AP calls for a check. I think this may be part of the reason it go rolled into acrobatic in the unchained consolidated skill rules. because it just get ignored all together so no one every put ranks. The fact that the rules really don't allow a character to even put ranks into it until level 7+ also puts a dampener on the skill. As you need a reliable way to fly before you can put a rank into it. At least using the unchained rules, It is a skill almost everyone puts some ranks in so if one of those checks come up you have a chance to make it.
I also notice most GM only use altitude as a factor and some like my self even ignore that and treat it like an fly is on off switch. you can melee attack all creatures that are also in flying status, only creatures with grounded status that can attack you are those with range weapons, or those your are in melee and that have the same reach as you. This limit the focus to just the 2d map we are using any way.
All altitude add to the game is extra paper work and book keeping that slows the game down. Same with the skill checks, it just slows the game down in combat. the system already and GM already has enough things slowing it down.
Ask your GM how he wants to run the fly rules, if it is by the book or if he want to ignore them. if this is PFS you are kind of stuck. Ignore them will speed up the game and give the GM less bs they have to worry about.