LOS Analyzer Methodology

Last updated: 2026-10-02

Purpose & Scope

LOS Analyzer is a preliminary screening aid for proposed structures near airports. It answers two early questions: does the structure block the control tower’s view of the runways, and does it penetrate any of the 14 CFR Part 77 imaginary surfaces? Use it to decide whether and how to file FAA Form 7460-1, to compare design options, and to prepare a filing.

It is not an FAA determination, an aeronautical study, a survey, or an engineering review. Only the FAA issues determinations. A CLEAR result does not mean FAA notice is not required: whether 14 CFR 77.9 requires notice is the proponent’s determination, and when in doubt, file. See the Disclaimer.

Data Sources

Automated sources:

• FAA NASR (28-day subscription): runway ends, threshold elevations and airport data. The bundled snapshot is rebuilt automatically each AIRAC cycle. Part 77 surfaces are computed only when an airport with FAA runway data is linked.
• Terrain elevation: USGS National Elevation Dataset (10 m) served by the public OpenTopoData API, sampled along each sightline. Typical vertical accuracy is ±5–15 ft and varies by region.
• Google Maps Platform: satellite imagery for the map and report, and airport search (geocoding).
• Seeded tower data: approximate control-tower positions and controller eye heights for 24 US airports. Eye heights are derived estimates (medium confidence) using the FAA Order 6480.4B convention (eye ≈ cab floor + 5 ft), not surveyed values. The app flags them and you should replace them with verified values.

User inputs (the critical path):

• Tower position and controller eye height (ft above ground): pre-filled where seeded, always editable.
• Building footprint: corners clicked on the satellite map or typed as coordinates.
• Building height above local ground, in feet.
• Runway ends and Part 77 classification: runway ends come from FAA data for the linked airport; each end’s approach classification is inferred from NASR and can be overridden.

Line of Sight (3D, terrain-aware)

For each tower and runway target, the engine samples the ground path from the tower to the target and tests whether terrain or the proposed building blocks the straight line from the controller’s eye to the target.

• Terrain: elevations are sampled along the path. If the elevation service is unavailable, the engine falls back to flat ground at the airport elevation, and the report says so.
• Earth curvature and refraction: the line of sight is lowered by the earth “bulge” using the standard aviation convention, drop(d) = d² / (2·k·R) with R = 6,371 km and k = 7/6 (normal atmospheric refraction, ITU-R P.834).
• The building is modelled as a flat-topped prism of the stated height above the local ground inside its footprint. It blocks a sightline where the ground path crosses the footprint and the prism reaches the line of sight.
• Runway coverage: sightlines run to the runway thresholds and to points along each runway (start to end), and a fan of rays from each tower is drawn on the map to show the shadow the building casts.
• Horizontal distances use a local flat projection, accurate to better than 0.1% at airport scale.

Part 77 Imaginary Surfaces

Surfaces are computed from the FAA runway data per 14 CFR Part 77, Subpart C, and the dimension tables for each runway end’s approach classification (visual, non-precision instrument, precision instrument):

• Primary, horizontal, conical, approach and transitional surfaces.
• The primary surface elevation is interpolated between the runway’s threshold elevations.
• Horizontal and conical surfaces use the stadium shape (arcs around each runway end, joined by tangents).
• Approach surfaces are modelled from each runway’s threshold end.
• The top of the structure (ground elevation from the terrain sample inside the footprint, else the airport elevation, plus the building height) is tested against each surface, and any penetration is reported in feet.

Form 7460-1 Pre-fill Aid

From the same inputs, the app prepares a draft of the structure and location fields of FAA Form 7460-1. It never invents proponent details. The proponent must verify every value before filing, including NAD83 coordinates and a site elevation to the accuracy the FAA requires (a DEM elevation is an estimate, not a survey), and files through the FAA’s OE/AAA portal.

Known Limits & Assumptions

• Local obstructions are not modelled: trees, existing buildings, poles and cranes.
• Terrain accuracy is limited by the public elevation model (typically ±5–15 ft).
• Standard refraction only: temperature inversions and other non-standard conditions are not modelled.
• Simple building geometry: a single flat-topped prism; setbacks, spires and antennas are ignored unless you include them in the height.
• Tower inputs: seeded eye heights are derived estimates; tower position and eye height drive the line-of-sight result, so verify them.
• Coordinates are WGS84 (Google); the FAA works in NAD83 and may require surveyed accuracy.
• Data currency: FAA runway data follow the 28-day cycle of the snapshot in use.
• Not modelled at all: obstruction lighting and marking, TERPS / instrument-procedure surfaces, navaid and radar interference, and runway visual-range requirements. The FAA evaluates these in its own study.

Comparison to FAA Processes

LOS Analyzer is a pre-screen before the Form 7460-1 filing. It shows where a design stands against the surfaces and the tower’s view, so you can adjust the design or prepare the filing. It never replaces the FAA’s determination or a licensed professional’s judgement.

Public FAA Records on This Site

The FAA case lookup, The Docket and the data reports republish and summarise records from the FAA’s Obstruction Evaluation / Airport Airspace Analysis (OE/AAA) public archive. Each one shows the date of the archive it was built from. They are not an official FAA record or an FAA determination; the FAA’s portal at oeaaa.faa.gov is authoritative.

• Names on the case pages. Representatives are shown as they appear in the FAA’s public record, including named professionals who file on a sponsor’s behalf. Filings by private individuals as sponsors are excluded. We identify those from the name on the record, so one can slip through.
• Corrections and removals. If a record here is wrong, or a name should be corrected or removed, email support@idea-engine.studio.

References & Further Reading

• 14 CFR Part 77: Safe, Efficient Use, and Preservation of the Navigable Airspace (eCFR).
• FAA Order JO 7400.2: Procedures for Handling Airspace Matters.
• FAA Order 6480.4B: Airport Traffic Control Tower Siting Process.
• FAA AC 150/5300-13B: Airport Design.
• FAA OE/AAA portal: oeaaa.faa.gov, for filing Form 7460-1.

Questions? Email support@idea-engine.studio. LOS Analyzer is a product of Idea Engine LLC and is not affiliated with or endorsed by the FAA.