Careful FlyerSource Ultimate Intrigue pg. 79
You move with ease when you fly at a slower rate.
Prerequisites: Acrobatic, Fly 5 ranks.
Benefit: As long as you take a move action to fly, even when moving less than half your speed, you do not need to succeed at a Fly check to continue flying. When moving less than half your speed in a round, you also gain a +2 bonus on Acrobatics checks to avoid attacks of opportunity and a +2 bonus to your AC against attacks of opportunity you provoke because of movement.
Normal: You must succeed at a Fly check to continue flying unless you move at least half your speed.