Multiple forms of flight on the same creature, what happens?

An old enough dragon can learn spells that grant flight with improved maneuverability. There are the Wings of Air and Wings of Air, Greater spells (cannot link as they are not OGL). That can get a dragon from Clumsy maneuverability to Average. But, a good old-fashioned Fly spell can give them a 60ft fly speed with Good maneuverability.

Fly speeds do not stack. But how do maneuverabilities work? If a dragon casts Fly on themselves, can they move with good maneuverability so long as they only move 60 ft in the round, but if they move their full 250, they have whatever maneuverability is associated with that speed (probably clumsy)? Or, do they wind up with 250 ft fly speed with Good maneuverability for the duration of the Fly spell? Or does the Fly spell make their wings inoperable, and they have 60 ft fly speed with Good maneuverability only?

• Not a duplicate question, but it does inform a lot of what the answer to this one must be: Questions about flying and switching between modes of movement when flying Commented Feb 4, 2021 at 18:02
• @KRyan That is a great reference, and that solution could work. At 250 ft. movement with clumsy maneuverability, the dragon can turn a maximum of 45 degrees in a single move action. So, using 5ft of movement from the Fly spell, which corresponds to 250*(5/60) = 21 ft of movement (round up to 25 ft of movement) for the dragon's flight, they can turn 90 degrees? I think I like that. It is a mix between Good and Clumsy maneuverability. Not ideal, but not bad either. Commented Feb 4, 2021 at 18:14

No one knows

The game simply does not have rules for multiple movement speeds and how you can or cannot use them together. I have looked high and low, and it just does not exist. So it’s not at all clear even if you can switch from a good-maneuverability flight speed to an average-maneuverability one, much less how that would affect the actual movement you get from each.

The ruling I have settled on is this:

Your total movement cannot exceed the highest speed from among all the movement modes you have, nor can any individual type of movement exceed its own speed.

That is to say, if you have 60-ft (average) speed and 40-ft (good) speed, you could fly up to 60 feet total, but you couldn’t fly more than 40 feet of it with good maneuverability. For the other 20 feet, you’d need to use average maneuverability.

This doesn’t matter terribly much most of the time for different flight maneuverabilities, but it can matter very much for different types of movement speed, e.g. running for a bit before taking off.

And this ruling is simple to implement and run, and avoids a ton of issues trying to be more accurate about things.