Quote Originally Posted by tony
On one hand I want to say the headwind will actually push the 747 back keeping it on the conveyor BUT that same headwind could aid it in taking off.. even if the plane was not moving.

So I'll go with yes, it will still take off.
Actually, it will appear to "hover" in the air and not move forward or backwards if the wind is strong enough to keep it from going forward, but weak enough to not push it back. I know this because I have flown RC planes into strong headwinds and seen this effect with my own eyes.