I think these things depend mostly on the types and numbers of such questions.
If there are clearly two distinct types of questions accumulating in a single tag then it might be worth dividing them.
But if there's only two or three questions of one type then it's probably not going to change anything for any real users or use cases. How many helicopter questions do we have? Does it appear we will keep accruing more and more of them? Are they hard to find by searching for "helicopter"?
If we do divide them it will then not make sense to leave the airplane category to be named "air travel" when it now only includes a subset of air travel questions.
Which leaves the rare questions about air travel that are not about planes or helicopters (or cover both). For instance would airship/zeppelin/hot air balloon questions need their own tag? Would the plane tag need to specifically cover those other options? Would we also need to split out a third tag just to cover them?
All these implications must be looked into besides just the surface question of "Why are there so many plane questions mixed in with the few chopper questions under the same tag?" Because while it can be phrased to appear as though it's a problem, you have to look deeper to decide whether there is actually a problem or just an imagined one, then ponder a bit to decide the best solution to the problem.
Don't rush to solve one minor problem by creating a new minor problem and in the meantime solve no major problems. Rather analyse the situation fully, then implement a solution, if we even need one.