Which statement about the Conical Surface is true?

Which statement about the Conical Surface is true?

• A. Starts at the primary surface centerline and descends.
• B. Ends at the perimeter of the horizontal surface and continues downward at a slope of 10:1 for 2,000 ft.
• C. Starts at the perimeter of the horizontal surface and continues upward at a slope ratio of 20:1 for a horizontal distance of 4,000 ft.
• D. Begins at the runway threshold with a slope of 50:1.

Answer: (C)

The Conical Surface is an obstacle limitation surface that starts at the outer edge (perimeter) of the horizontal surface and then extends outward and upward. It uses a gentle slope of 20:1 (that is, 20 units horizontally for every 1 unit of vertical rise) for a horizontal distance of 4,000 feet. So, at 4,000 feet from the horizontal surface edge, it rises about 200 feet above that surface. This is why the statement describing starting at the horizontal surface perimeter and climbing upward at a 20:1 slope for 4,000 feet is true. The other descriptions don’t fit because they describe incorrect starting points or directions: starting from the centerline and descending would not define the conical surface; ending at the horizontal perimeter and continuing downward is the opposite direction; and beginning at the runway threshold with a 50:1 slope uses the wrong origin and an incorrect ratio.

The Conical Surface is an obstacle limitation surface that starts at the outer edge (perimeter) of the horizontal surface and then extends outward and upward. It uses a gentle slope of 20:1 (that is, 20 units horizontally for every 1 unit of vertical rise) for a horizontal distance of 4,000 feet. So, at 4,000 feet from the horizontal surface edge, it rises about 200 feet above that surface. This is why the statement describing starting at the horizontal surface perimeter and climbing upward at a 20:1 slope for 4,000 feet is true.

The other descriptions don’t fit because they describe incorrect starting points or directions: starting from the centerline and descending would not define the conical surface; ending at the horizontal perimeter and continuing downward is the opposite direction; and beginning at the runway threshold with a 50:1 slope uses the wrong origin and an incorrect ratio.