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OCR for page 74
74 Guidebook for Managing Small Airports Airspace and Approaches The purpose of this section is to provide guidance on issues pertaining to airspace clearing and obstruction standards including a review of 14 CFR Part 77, Objects Affecting Navigable Airspace; TERPS; and airspace right-of-way and easements. 14 CFR Part 77, Objects Affecting Navigable Airspace (FAR Part 77) FAR Part 77 establishes the standards for determining obstructions to navigable airspace and describes the notification requirements for any construction or alteration potentially affecting navigable airspace surrounding airports. Standards Imaginary Surfaces. The navigable airspace areas governed by FAR Part 77 are referred to as "imaginary surfaces." The size and shape of imaginary surfaces are dependent on the size of air- planes that use the airport, the approach visibility minimums, and the runway type (e.g., paved or turf). Figure 5 illustrates dimensions for some of the imaginary surfaces. The FAA Obstruction Evaluation/Airport Airspace Analysis page of the FAA website ( external/portal.jsp) provides a link to FAR Part 77 dimensional requirements and illustrations for imaginary surfaces as well as other information relating to the process for reviewing airspace issues. The five types of imaginary surfaces are Primary Surface. A primary surface is a surface longitudinally centered on a runway. When the runway has a specially prepared hard surface, the primary surface extends 200 feet beyond each end of that runway; when the runway has no specially prepared hard surface, or planned hard surface, the primary surface ends at each end of that runway. The elevation of any point on the primary surface is the same as the elevation of the nearest point on the runway centerline. The width of a primary surface is 250 feet for utility runways having only visual approaches or 500 feet for utility runways having nonprecision instrument approaches. For other than utility runways, the width is 500 feet for visual runways having only visual approaches; 500 feet for nonprecision instrument runways having visibility minimums greater than three-fourths of a statute mile; or 1000 feet for precision instrument runways, and for nonprecision instrument runways hav- ing a nonprecision instrument approach with visibility minimums as low as three-fourths of a statute mile. The width of the primary surface of a runway will be that width prescribed for the most pre- cise approach existing or planned for either end of that runway. Transitional Surface. The transitional surface extends outward and upward at right angles to the runway centerline and extends at a slope of 7 feet horizontally for each 1 foot vertically (7:1) from the sides of the primary and approach surfaces. The transitional surfaces extend to the point at which they intercept the horizontal surface at a height of 150 feet above the established airport elevation. For precision approach surfaces that project through and beyond the limits of the conical surface, the transitional surface also extends 5,000 feet horizontally from the edge of the approach surface and at right angles to the runway centerline. Horizontal Surface. The horizontal surface is a horizontal plane located 150 feet above the estab- lished airport elevation that encompasses an area from the transitional surface to the conical sur- face. The perimeter is constructed by generating arcs from the center of each end of the primary surface and connecting the adjacent arcs by lines tangent to those arcs. The radius of each arc for all runway ends designated as utility or visual is 5,000 feet and 10,000 feet for precision and non- precision runway ends.

OCR for page 74
Airport Planning and Development 75 Figure 5. FAR Part 77 imaginary surfaces.