Where does the outer horizontal surface begin?

Where does the outer horizontal surface begin?

• A. At the edge of the outer horizontal surface
• B. At the edge of the runway centerline
• C. At the edge of the conical surface
• D. 10,000 ft from the runway centerline

Answer: (C)

Outer horizontal begins where the conical surface ends. Obstacle limitation surfaces around a runway are defined in a stepped sequence: inner horizontal near the runway, then the conical surface that slopes upward outward, and beyond that the outer horizontal plane. The boundary between the conical surface and the outer horizontal marks the start of the outer horizontal. The other options don’t fit because the start isn’t at the edge of the outer horizontal itself, nor at the runway centerline edge, and it isn’t a fixed distance like 10,000 ft—the boundary is defined by the conical surface.

Outer horizontal begins where the conical surface ends. Obstacle limitation surfaces around a runway are defined in a stepped sequence: inner horizontal near the runway, then the conical surface that slopes upward outward, and beyond that the outer horizontal plane. The boundary between the conical surface and the outer horizontal marks the start of the outer horizontal. The other options don’t fit because the start isn’t at the edge of the outer horizontal itself, nor at the runway centerline edge, and it isn’t a fixed distance like 10,000 ft—the boundary is defined by the conical surface.