>>8968488Optimus didn't "always have the ability to fly" in the G1 cartoon. This was the case from the beginning of the series, when in the third episode (More Than Meets the Eye, Part 3), he had to borrow Sideswipe's jetpack in order to fly, all the way to the end of the series when in the season three finale (The Return of Optimus Prime, Part 2), he fell into a pit while Galvatron remarked that Autobots can't fly.
Megatron though, yeah, he could always fly, same with guys like Soundwave and Reflector who didn't have aerial alt modes. All the Decepticons pretty much could.