The Sky Has a Ceiling: How FAR Part 77 and Military Airfield Criteria Limit Building Heights Near Runways

Aerial view of a military airfield runway with translucent imaginary airspace surfaces — approach, transitional, horizontal, and conical surfaces — overlaid as a planning diagram.

The first time I watched a developer learn about imaginary surfaces, it was in a conference room with a site plan on the table. The project was a mid-rise hotel near an airfield — good location, good market, straightforward entitlements. Then someone slid the airfield airspace map across the table, and the developer’s face changed. The building’s top floors sat inside an invisible wedge of protected airspace extending off the runway end. The hotel did not need to move far. But it did need to get shorter, or the project was dead.

Every runway in America carries an invisible three-dimensional shape around it. Planners, developers, and installation teams ignore it at their peril. For civilian airports, that shape comes from Federal Aviation Regulation Part 77. For military airfields, it comes from the Department of Defense’s own rulebook, UFC 3-260-01. I work in the overlap between those two worlds, and I can tell you from experience: the sooner a project accounts for airspace surfaces, the cheaper the lesson is.

What Part 77 actually is

Part 77 is a section of Title 14 of the Code of Federal Regulations — 14 CFR Part 77, administered by the Federal Aviation Administration. It does two things. First, it defines imaginary surfaces: geometric shapes in the sky around airports that must stay clear of obstructions. Second, it requires anyone proposing construction that might pierce those surfaces to notify the FAA before building, so the agency can study whether the structure is a hazard to air navigation.

The key point most people miss: exceeding an obstruction standard does not automatically make a structure a hazard. It triggers a study. The FAA’s aeronautical study looks at the effect on existing and planned flight operations, navigation and radar systems, and airport capacity, then issues a formal determination — hazard or no hazard. But no developer wants that determination hanging over a project. Smart planners keep structures below the surfaces from the start.

The five imaginary surfaces

The imaginary surfaces are easiest to picture as a set of nested shapes wrapped around the runway:

  • Primary surface. A flat rectangle centered on the runway itself, extending slightly beyond each runway end. Nothing sticks up through this except the runway’s own equipment.
  • Approach surface. A long, flaring wedge extending outward and upward from each runway end, aligned with the extended runway centerline. Its slope and length depend on the type of instrument approach the runway supports — a precision approach gets a long, shallow surface, sometimes at a 50:1 slope, while a visual runway gets a shorter, steeper one.
  • Transitional surface. Sloped planes along the sides of the primary and approach surfaces, rising outward at a 7:1 slope until they reach the horizontal surface.
  • Horizontal surface. A flat plane 150 feet above the established airport elevation, drawn as arcs around each runway end.
  • Conical surface. A funnel extending outward and upward from the edge of the horizontal surface at a 20:1 slope.

Together, these form a bowl of protected airspace. Anything that pokes through the bowl — a tower, a crane, a rooftop antenna — is an obstruction by definition, and the proposer has to deal with it.

When you have to notify the FAA

Part 77’s notice requirements are broader than most people expect. The headline trigger is simple: any proposed construction or alteration more than 200 feet above ground level, anywhere in the country, requires FAA notice. But there are others that catch projects much closer to the ground near airports. One of the most important: any structure that would exceed a 100:1 slope extending outward from the runway for 20,000 feet at an airport whose longest runway exceeds 3,200 feet. Near a busy airport, that slope starts cutting close to the ground fast — at 10,000 feet from the runway, the limit is only 100 feet above runway elevation.

Notice goes to the FAA on Form 7460-1, the Notice of Proposed Construction or Alteration, filed through the agency’s Obstruction Evaluation/Airport Airspace Analysis process. The rule is to file at least 45 days before construction begins, and in practice I tell project teams to file much earlier — an unfavorable determination late in design is one of the most expensive surprises a project can get.

One detail that routinely trips up planners: traverse ways count. Roads and railroads near an airfield are treated as obstructions, with added heights for the vehicles on them — 17 feet for an interstate highway, 15 feet for other public roads, 23 feet for a railroad. A new highway interchange near a runway end is not just a transportation project; it is an airspace project.

Military airfields have their own rulebook

Military airfields do not live under Part 77 the way civilian airports do. The Department of Defense sets its own airfield planning criteria in UFC 3-260-01, Airfield and Heliport Planning and Design. The concepts rhyme with Part 77 — the UFC defines its own primary surfaces, approach-departure clearance surfaces, transitional surfaces, inner and outer horizontal surfaces, and conical surfaces — but the dimensions reflect military aircraft, military missions, and the reality that a fighter jet climbs differently than a regional airliner.

When Nathaniel Pyron works with installation teams on airfield planning, the airfield obstruction map is one of the first documents pulled out. Every structure on the installation is measured against the UFC surfaces, and anything penetrating them is tracked in the installation’s airfield obstruction management program. Violations require formal waivers approved at the service level — a process nobody enjoys. Keeping the master plan’s building heights and locations inside the surfaces from day one is always cheaper than waiving an obstruction after it is built.

The civilian-military overlap is where things get interesting. A city near a military base does not answer to the UFC, and the base does not answer to the city’s zoning code. That coordination happens through the AICUZ program and joint land use studies — tools I have written about in this series — where the installation shares its airfield surfaces with the community so local height zoning can mirror them. When it works, the community’s zoning map and the base’s obstruction map tell the same story.

What this means for master planning

For the planner, airspace surfaces are a design constraint like topography or wetlands — invisible, non-negotiable, and much easier to handle early than late. Three habits keep projects out of trouble:

  1. Pull the airspace map before the site plan. Whether it is the FAA’s Part 77 surfaces or the installation’s UFC obstruction map, the surfaces should be a base layer in the GIS before any building footprint is drawn.
  2. File the 7460 early. If a project is anywhere near an airport or military airfield, submitting the FAA notice during schematic design costs almost nothing and buys certainty. Waiting until permitting can kill a timeline.
  3. Design the skyline downward, not upward. The most successful airfield-adjacent developments I have seen treat the approach surface as a design feature — stepping building heights down toward the runway end. It reads as intentional urban design, and it happens to be exactly what the airspace requires.

Runways do not negotiate. Their protected airspace is drawn in regulation, measured in feet, and enforced by physics as much as by law. The planner’s job is to make sure everyone building nearby knows where the invisible ceiling is — before they hit it.

About the author

Nathaniel Pyron is a military urban planner specializing in military master planning, with an airport and airfield planning focus. He spent three years with the United States Marine Corps as a community planner at Camp Blaz and Darwin, Australia, and studied urban planning at Arizona State University’s School of Urban Planning. Based in Honolulu, Hawai’i, he writes about the intersection of military installations and the communities around them.

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