Basically just echoing what Ax109 said here:
The only potential form of "flying" that you can do in PLZA is called Roto-Gliding. This is unlockable by going up the ladder behind hotel Z during main mission 15. On the roof, you find your rival, who teaches you to Roto-Glide upon interaction. However, this can not be used from the ground, only as a boost in the air when, for example, you're jumping in between rooftops. Also note that this can only be used once per air time, and recharges once you touch a solid surface again.
Source
