Imaginary Surfaces / Obstruction Clearance FAA Part 77
Federal airspace-protection rules that cap how tall you can build near airports.
Overview
Federal airspace-protection rules that cap how tall you can build near airports.
Agency
Federal Aviation Administration (FAA)
Enacted
1965
Last reviewed
2026-04-19
Overlays in file
1
Why it matters
Every structure taller than the Part 77 notice thresholds triggers a Form 7460-1 filing. The FAA can block an otherwise zoning-compliant building on airspace grounds — this is the most common way a municipal height bonus gets silently capped by federal law.
When to worry
If your site is within ~20,000 ft of a public-use airport runway, or under a transitional/approach surface. The trigger surfaces are primary, horizontal, conical, approach, and transitional — each with its own geometry relative to the runway.
FAA Part 77 Imaginary Surfaces — Obstruction Height Preemption
Authority
federal
Scope
federal
Effective
1965-02-01
Federal-conflict flag
Not flagged
Citation
Authority source
14 CFR Part 77 — Safe, Efficient Use, and Preservation of the Navigable Airspace
§ 14 CFR §77.17 (standards), §77.19 (civil airports), §77.21 (military airports)
Trigger predicate
When this predicate evaluates true for a parcel, the overlay applies.
AND
city.airport_influence_zonesattribute is presentcity.airport_influence_zones[].kindcontainsPart_77
Preempted fields
The operations that federal rule forces onto the base zoning when the predicate fires.
| Field | Op | Value | Note |
|---|---|---|---|
base_districts[*].max_height_ft | cap_at | variable-by-parcel-geometry | Part 77 imaginary surfaces (primary, horizontal, conical, approach, transitional) generate a parcel-specific height ceiling. The evaluator flags federal height constraint; exact cap must be resolved at parcel level by querying the surface geometry for that airport. |
Notes
Per-parcel surface computation required. This overlay flags that height at the parcel is federally-constrained but does not resolve the exact cap at the city level. The predicate scans city.airport_influence_zones[] for any entry whose kind=='Part_77'. Downstream specialists must call the FAA OE/AAA (Obstruction Evaluation / Airport Airspace Analysis) or use published FAR Part 77 surface rasters to resolve the actual ceiling for a given parcel. Notice of Proposed Construction (FAA Form 7460-1) is required for any structure exceeding the notice thresholds in §77.9.