Other problems: - It may not be possible to arrange landing areas in the desired direction - Vehicles may not be able to make sufficiently tight turns - Fixed-wing vehicles cover quite a large vertical distance, especially when rolling as they turn due to wingspans. There's plenty of room for converging paths, and your rules may not allow enough leniency to avoid such paths. A "slight graze" that takes off half a wing is not acceptable. - Parallel lines converge on the surface of the world. Two planes flying due north (X is a multiple of 360) may collide at or near the poles.