Definition: conical surface (Applicable to Article IV - Chapter 1)
The "conical surface" is an imaginary inclined surface extending upward and outward from the periphery of the horizontal surface , which: (a) rises at a slope, measured in an imaginary vertical plane passing through the airport reference point (or points ), of one foot for every 20 feet in horizontal distance; and (b) is measured on a horizontal radius from the airport reference point (or points ), and extends for a distance set forth in Section 61-41 (Airport Reference Point, Established Elevation and Specified Radii).