What is the maximum height a sUAS can fly above a taller building within a 400-foot radius?

The correct answer is based on the FAA's regulations regarding the operation of small Unmanned Aircraft Systems (sUAS) in relation to buildings. The regulation states that a sUAS may not fly higher than 400 feet above ground level unless it is within a 400-foot radius of a structure.

In the context of this regulation, if a sUAS is operating near a tall building, it is permitted to fly up to 400 feet above the highest point of that building. This means that the sUAS could potentially exceed 400 feet above the surrounding terrain, as long as it remains within that specified radius from the structure.

Therefore, the maximum height a sUAS can legally fly is precisely 400 feet above the tallest building within that operational radius, making the choice of 400 feet accurate in accordance with the regulations.