Gyarados has some of the highest HP stats in the game, complemented by great Attack, Defense, Speed and Special ratings. While it can't learn Fly (or any other Flying attacks) in Blue, Red or Yellow, it is able to learn a range of powerful non-Water/Flying attacks from HMs and TMs.

Does gyarados fly type?

3 "Gyarados is one of eight non bug, flying-type pokémon that can't learn Fly."

Can gyarados ever learn fly?

It's still hotly debated why Gyarados is a Flying-type Pokémon when it would arguably be better suited as a Dragon- or Dark-type, but either way, it can still learn Flying-type moves like Hurricane and Bounce. This is why trainers may be surprised to realize it's unable to learn the move Fly.