Protection of navigable airspace from obstructions that can be hazards to aircraft flight requires establishment of limits on the height of structures, trees, and other objects. Navigable airspace is defined by the FAA pursuant to Title 14 of the Code of Federal Regulations Part 77, Imaginary Surfaces, referred to herein as Federal Aviation Regulations (FAR) Part 77 Surfaces. FAR Part 77 surfaces are those air spaces above and around airports that require protection from potential obstructions that might interfere with airport traffic and potentially create a safety risk to aircraft occupants and citizens on the ground.

An object or structure with an elevation higher than the FAR Part 77 Surface elevation is considered to penetrate the FAR Part 77 Surface and constitute an obstruction to navigable airspace. The vertical elevations of the FAR Part 77 Surfaces are determined above the runway elevation and are based on the approach classification of the runway (Map 33.08.020 (1b)). Based on existing topography and the FAR Part 77 Surfaces elevations, height hazard areas are identified where structures and other obstructions have a high likelihood of penetrating a FAR Part 77 Surface. The boundary and elevation of the FAR Part 77 Surfaces relative to the ground topography and the height hazard area is designated and shown on Map 33.08.020 (1b).