I can't find anything about this in the PHB, but it seems to me that it would make sense to include some kind of penalty when making a ranged attack against a moving target, especially if it is moving fast.
For the archer, a massive orc standing in front of the tank is surely easier to hit than an eagle plunging down on some other party member at full speed. Sure, the archer can try to predict the target's trajectory, and might be able to hit nevertheless, but it will definitely be harder.
Yet, as long as the target is within range (as far as I can see from the rules), a normal attack roll is made against the opponent's AC in both cases. The AC may model the armor's quality, the dexterity of a target, perhaps even some shielding buff, but it does not include the speed a target is moving at.
Wouldn't it make sense, for instance, to impose disadvantage on the attack roll in a situation where the target of a ranged attack is moving rapidly, such as in the case of the plunging eagle?