Definition: transitional surfaces (Applicable to Article VI - Chapter 1)
The "transitional surfaces" are imaginary inclined planes extending upward and outward from the side edges of all approach surfaces , and from lines parallel to, 500 feet from, and at the same level as the center line of each runway, which: (a) rise at a slope of one foot in height for every seven feet of horizontal distance measured in a vertical plane at right angles to the center line of the runway; and (b) extend to the point of intersection with the horizontal surface or the conical surface .