Where does the transitional surface begin?

Where does the transitional surface begin?

• A. at the edge of the inner horizontal
• B. at the lateral edge of the primary surface
• C. at the outer edge of the runway
• D. at the centerline of the runway

Answer: (B)

Transitional surfaces start at the lateral edge of the primary surface. These imaginary surfaces grow upward and outward from that boundary to protect airspace around the runway, typically with a fixed slope. Starting at the outer edge of the primary surface keeps the starting point tied directly to the defined protected zone of the runway, ensuring obstacle heights are considered from where the primary surface ends. So the correct starting point is the side boundary of the primary surface. The inner horizontal boundary, the outer edge of the runway beyond the primary surface, or the centerline do not align with how transitional surfaces are defined to begin.

Transitional surfaces start at the lateral edge of the primary surface. These imaginary surfaces grow upward and outward from that boundary to protect airspace around the runway, typically with a fixed slope. Starting at the outer edge of the primary surface keeps the starting point tied directly to the defined protected zone of the runway, ensuring obstacle heights are considered from where the primary surface ends. So the correct starting point is the side boundary of the primary surface. The inner horizontal boundary, the outer edge of the runway beyond the primary surface, or the centerline do not align with how transitional surfaces are defined to begin.