Would Gust of Wind (and other spells) cause flying creature to stall?

Question

Flying creatures need a minimum forward speed to be able to fly.

Minimum Forward Speed: If a flying creature fails to maintain its minimum forward speed, it must land at the end of its movement.

So let's take a harpy with a base fly speed of 80ft (average). and imagine that she flies towards a wizard who has readied Gust of Wind to be triggered just before the harpy reaches the him. The harpy has already moved 60ft and is then blown back 1d6x5ft. by the Gust of Wind effect.

Gust of Wind: This spell creates a severe blast of air (approximately 50 mph) that originates from you, affecting all creatures in its path. Medium creatures are unable to move forward against the force of the wind, or if flying are blown back 1d6×5 feet.

Now what would to the harpy?

• Would she stall immediately because her forward speed dropped to zero by being blown back?

• Would she continue with her remaining 20ft. of movement and then stall (or be forced to use her second action as a move action)?

• Would she continue with her remaining 20ft. of movement, not stall and be able to take a standard action?

I suppose RAW the latter would be the case, because she has done 40ft. of movement necessary to keep flying in her round.

What about other spells / powers? Imagine the same situation with the following:

• Telekinesis to grapple the harpy, winning the check and making her unable to move.

• Psionic Blast which stuns the harpy, making her unable to take an action.

Answer 1

Slow down there, WotC!

Unfortunately, the D&D 3.5e rules text for flying makes a muddy mess of a few spots, and this is one of them. The concept of "minimum forward flight speed" is a sensible thing in and of itself (it's imported from real-life winged flight), but what WotC fails to do is specify whether it's talking about the flyer's motion relative to the surrounding air (airspeed) or the flyer's motion relative to the ground underneath them (groundspeed).

In reality, the concept of "minimum forward flight speed" is all about airspeed -- a wing needs air moving over it to generate lift, but doesn't care about the details of what's generating that airflow. If you're the wing, moving through a still airmass is no different than being mounted on a sturdy pole in a stiff breeze, even.

As a result of this, your hypothetical harpy would still consume her full 80' of movement in a turn even if the wind is pushing her back -- its just that the headwind means she didn't get the full benefit of the 80' of movement expended in terms of getting to the point B she was trying to reach. In other words, for a Gust of Wind casting and a flying character, consume all the movement the flying character was trying to use, then apply the forced movement of the Gust of Wind. (Mathheads will recognize this as vector addition.) This also has the benefit that it handles a creature that's not flying towards the caster properly -- they might get kicked sideways by the spell, or even gain a boost to their getaway from it.

Grabbing something is not the same as blowing it around

On the other hand, effects that actually influence the creature's movement relative to the air around it, like Telekinesis, can cause a flyer to drop below its minimum movement, as the character at that point can't move through the air surrounding it, never mind making any headway relative to terra firma! Likewise, a stunned flyer can't use any of their movement allowance, so clearly they'll go nowhere but down.