Plane picks up ad banner

You've all seen advertisement banners being pulled by airplanes. Few of you have thought about the logistics of it. From Now I know:

Most of the planes that carry these signs are rather small, and attempting to take off with the sign already in tow would throw off the plane’s center of gravity, preventing it from getting airborne. Carrying the furled up sign in the cockpit or (typically tiny) payload runs the very real risk of getting it tangled up with the aircraft itself, resulting in disaster. In short, the plane can’t take off with the sign already attached.

Instead, the plane, already in flight, picks the sign up off the ground.

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