CFR Part 77 VFR Surfaces

CFR Part 77 Surfaces

CFR Part 77 establishes a complex structure of imaginary surfaces in relation to each runway at airports or helipads.  The size of each imaginary surface is based on the category of each runway according to the type of instrument approach available or planned for that runway. 

According to the provisions set forth in Part 77, an object is an “Obstruction to Air Navigation” if it is of greater height than any imaginary surface established under the regulation.

Imaginary surfaces exist primarily to prevent existing or proposed manmade objects, objects of natural growth, or terrain from extending upward into navigable airspace.

The Federal Aviation Administration (FAA) has applied to public-use airports, military-use airports, and helipads for the purpose of determining obstructions to air navigation. 

These imaginary surfaces either slope out and up from all sides and ends of runways or are a horizontal plane or a sloping plain above airports and helipads.

CFR Part 77 imaginary surfaces include:

77.9 Construction or Alteration Requiring Notice

77.17 Obstruction Standards

77.19 Civil Airport Imaginary Surfaces

  • 77.19 (a) Horizontal Surface: Horizontal plane 150 ft. above the established airport elevation.  Constructed by swinging arcs around the end of the primary surface.

  • 77.19 (b) Conical Surface: 20:1 slope surface extending beyond the horizontal surface.

  • 77.19 (c) Primary Surface: Aligned longitudinally with each runway and extends 200 ft. from each runway end.

  • 77.19 (d) Approach Surface: Longitudinally centered with the runway and extends beyond the primary surface.

  • 77.19 (c) Transitional Surface: Constructed to join approach and horizontal or approach and transitional surfaces.

77.21 Department of Defense (DOD) Airport Imaginary Surfaces

  • 77.21 (a) (1) Inner Horizontal Surface: Horizontal plane 150 ft. above the established airport elevation,  constructed by swinging arcs around the end of the primary surface.

  • 77.21 (a) (2) Conical Surface: 20:1 slope surface extending beyond the horizontal surface.

  • 77.21 (a) (3) Outer Horizontal Surface: Horizontal plane 500 ft. above the established airport elevation,  constructed by swinging arcs around the end of the conical surface.

  • 77.21 (b) (1) Primary Surface: Aligned longitudinally with each runway with a width of 2,000 ft.

  • 77.21 (b) (2) Clear Zone Surface: A surface located on the ground or water at each end of the primary surface, with a length of 1,000 feet and the same width as the primary surface.

  • 77.21 (b) (3) Approach Clearance Surface: Longitudinally centered with the runway and extends beyond the primary surface.

  • 77.21 (b) (4) Transitional Surface: Constructed to join approach and horizontal or approach and transitional surfaces.

77.23 Heliport Imaginary Surfaces

  • 77.23 (a) Primary Surface: The area of the primary surface coincides in size and shape with the designated take-off and landing area.

  • 77.23 (b) Approach Surface: The approach surface begins at each end of the heliport primary surface with the same width as the primary surface, and extends outward and upward.

  • 77.23 (c) Transitional Surface: These surfaces extend outward and upward from the lateral boundaries of the primary surface and from the approach surfaces.