While Dugtrio can learn some flying-type moves, such as Aerial Ace and Fly (in later games), these moves are not available for it to learn in FireRed.
Here's why:
* Move Tutors: FireRed uses move tutors, which are specific trainers that can teach your Pokemon certain moves. However, Dugtrio does not have access to a Fly tutor in this game.
* TMs and HMs: Dugtrio cannot learn Fly through TMs or HMs in FireRed.
Therefore, if you want your Dugtrio to learn Fly in FireRed, you will need to trade it to a later generation game where it can learn this move.