Obstruction Analysis — Tool Guide

Coming Soon 14 CFR PART 77 · ALL GUIDES

The Obstruction Analysis tool evaluates a list of surveyed obstacles against the FAA obstruction-evaluation surfaces for a runway — the 14 CFR Part 77 imaginary surfaces, the AC 150/5300-13B (Chg 1) approach Surfaces 1–6, and the OCS 7 instrument departure surface — and reports, for every obstacle, which surfaces contain it, the surface elevation above it, and any penetration, each line carrying its regulatory citation. You define the runway end-by-end, drop in your obstacles (typed, pasted, or CSV-uploaded), and press Analyze obstructions; the workspace returns a penetration summary, a per-obstacle results table with expandable per-surface detail, and a layered, CAD-ready DXF in 2D or 3D for ALP sheet production.

This tool is built and in pre-release — the catalog still lists it as Coming Soon while it finishes verification. This guide documents the full workflow as the tool actually behaves today.

Who It's For & When to Use It

Airport planners assembling the obstruction data for an Airport Layout Plan set, a planning study, or an airspace narrative — the work that today means plotting survey points against hand-drawn Part 77 surfaces and computing surface elevations cell by cell in a spreadsheet. Use it when you have surveyed obstacle data (an obstruction survey, tree survey, or proposed-development point list) and need to know which points penetrate which surfaces, by how much, and under which citation — and when you need that result as drafted linework rather than a list of numbers.

How to Use It

  1. Optionally identify the airport. In the Airport Identity Bar at the top, type an FAA LID or ICAO identifier (e.g. KDEN) and click Look Up. AvPlot pulls the facility from FAA NASR and shows its name, ident, elevation, and NPIAS category. If the only data available is from OurAirports, a non-authoritative source, a banner appears with Continue with OurAirports data / Stop — you must choose before the data is used. This step is optional; you can skip straight to manual entry.
  2. Define the runway (Step 1). Fill in both ends — Low end (near threshold) and High end (far threshold) — with designation, threshold elevation, threshold coordinates (Northing/Easting or Lat/Lon), runway width, classification (Large vs. Small aircraft), AAC, ADG, TDG, approach type, and visibility minimums. If you looked up an airport, the Prefill from airport runway picker appears: choose a runway and AvPlot converts the NASR threshold lat/lon to State Plane using the detected zone and fills the designations, elevations, and width. Set Airport elevation (ft MSL) if you have it; blank assumes the maximum runway-end elevation and records that as an assumption.
  3. Enter the obstacles (Step 2). Choose the Coordinate system (all obstacles) — State Plane Northing/Easting or Latitude/Longitude; lat/lon requires a State Plane zone code (the State Plane tool detects one). Then populate the obstacle grid: + Add obstacle for a blank row, Upload CSV for a comma/tab file, or paste tab/comma rows into the Paste from spreadsheet box and click Add pasted rows. Per obstacle you supply ID, description, the two coordinates, top elevation MSL, AGL height, an Existing flag, and the carry-through ALP fields (ground elevation, survey date, disposition). Up to 500 obstacles per run.
  4. Analyze (Step 3). Click Analyze obstructions. The tool derives the surface set for both ends from the coordinates, elevations, and approach types, evaluates every obstacle, and renders the results below.
  5. Read the results. The Result Block leads with a penetration summary band (obstacle count, penetration count, surfaces evaluated), then the controlling standard, the analysis Assumptions and Warnings, and the data vintage. The results table lists every obstacle — sorted worst penetration first — with a status tag (PENETRATES / CLEARS / OUTSIDE), controlling surface, penetration in feet, OCS-7 TODA-action flag, and disposition. Expand any row’s Evaluated surfaces drawer to see each surface, whether the obstacle is in its footprint, the surface Z elevation, penetration, clearance, and the citation for that surface.
  6. Export. Click Copy results table to put the table plus its citation and assumptions on the clipboard, or pick the DXF mode (2D plan or 3D surfaces), set a project name, and click Export DXF for layered CAD linework. Use Save Project / Load Project to keep named versions; the workspace also autosaves as you work.

Key Features

  • Part 77 imaginary surfaces. Primary, approach, transitional, horizontal, and conical surfaces per 14 CFR §77.19, with the approach footprint anchored 200 ft beyond the threshold per §77.19, and slope/dimensions resolved per end from the approach type — including the precision 50:1 first 10,000 ft then 40:1 profile.
  • AC 150/5300-13B (Chg 1) approach surfaces. Surfaces 1–6 per Tables 3-2, 3-3, and 3-4 (Figures 3-5, 3-6, 3-7), selected per end by approach type; APV and precision ends report Surface 5 and Surface 6 separately.
  • OCS 7 instrument departure surface. Sections 1–2 per AC 150/5300-13B Table 3-5, evaluated only for ends with instrument departure procedures, with clearway handling and a flag when an existing-obstacle penetration would require a TODA action.
  • Per-obstacle, fully cited results. Each surface whose footprint contains the obstacle, its surface elevation at that point, penetration or clearance in feet, the controlling surface (worst penetration, or least clearance when clear), and a regulatory citation per surface.
  • Airport Identity Bar with NASR prefill. Authoritative FAA NASR lookup with a source badge and cycle date, runway prefill with automatic lat/lon→State Plane conversion, and the mandatory OurAirports fallback banner so non-authoritative data can never be used silently.
  • Flexible obstacle entry. Manual grid rows, spreadsheet paste, or CSV/TSV upload; State Plane or lat/lon (with a zone code) for the whole set; up to 500 obstacles per run.
  • ALP data-table carry-through. Planner-supplied ground elevation, AGL height, survey date, and disposition (per AC 70/7460-1) pass through verbatim — never computed — so the output assembles directly into the ALP obstruction data table per FAA ARP SOP 2.00.
  • Copy and layered DXF export. One-click results copy with citation trail, plus a 2D-plan or 3D-surfaces DXF — surface footprints on dedicated layers, obstacle block inserts carrying the ALP fields and layered clear versus penetrating, leader annotations, a model-space summary table, and a runway centerline profile; 3D mode draws true-elevation surface boundaries and penetration stems.
  • Project save/load and autosave. Named project versions through the project manager, with debounced autosave of the whole workspace as you work.

FAA References

  • 14 CFR Part 77, §77.19 — civil airport imaginary surfaces: horizontal, conical, primary, approach, and transitional. The approach footprint anchors its inner edge 200 ft beyond the threshold per §77.19.
  • AC 150/5300-13B Chg 1, Airport Design — approach Surfaces 1–6 per Tables 3-2, 3-3, and 3-4 (Figures 3-5, 3-6, 3-7) and the OCS 7 instrument departure surface per Table 3-5.
  • AC 70/7460-1, Obstruction Marking and Lighting — basis for the planner-supplied obstacle disposition field.
  • FAA ARP SOP 2.00, ALP Review — format basis for the ALP obstruction data table assembled from the results.

Limitations & Disclaimers

AvPlot is technical planning production support — accurate enough for design reports, planning studies, and ALP narratives. It is not a replacement for stamped engineering or construction documents, and it is not an FAA aeronautical study: running this analysis does not substitute for an OE/AAA filing or an FAA obstruction determination. Verify all results against current FAA publications before use in official Airport Layout Plans or submittals.

  • Full TERPS final-segment (W/X/Y) evaluation is not included; AC 13B Surface 6 uses the TERPS VGS 30:1 surface per Table 3-4.
  • The precision transitional extension beyond the conical surface is not evaluated in beta.
  • The vertical datum is assumed NAVD88; obstacle elevations must be supplied on a consistent datum.
  • The primary surface elevation is interpolated between runway end elevations; a centerline profile survey is not used.
  • Disposition is a planner determination — the tool echoes it for the ALP table and never assigns one.

Related Tools

Tips & Best Practices

  • Let the airport lookup do the coordinate math. Looking up the airport and using Prefill from airport runway converts NASR thresholds straight to State Plane in the detected zone — faster and less error-prone than transcribing coordinates by hand.
  • Keep one coordinate system per run. The Coordinate system selector applies to all obstacles in the grid. If you mix State Plane and lat/lon sources, convert them to a single system before pasting; lat/lon entry also needs a State Plane zone code.
  • Match your vertical datum. The analysis assumes NAVD88. Make sure every top-elevation MSL value is on a consistent datum before you analyze.
  • Set the airport elevation when you know it. Leaving it blank makes the tool assume the maximum runway-end elevation — fine in a pinch, but it is recorded as an assumption in the Result Block, so supply the real value for a clean citation trail.
  • Read the Assumptions and Warnings every time. They state exactly what the engine inferred (assumed elevations, skipped surfaces, scope limits) and any OCS-7 TODA-action flags — review them before quoting a result in a report.
  • Use the per-surface drawer to defend a number. Expand Evaluated surfaces on any obstacle to see the controlling surface alongside every other surface, its Z elevation, and its citation — the detail you need for an ALP narrative or a reviewer’s question.
  • Disposition is yours to assign. The tool echoes the disposition field verbatim for the ALP table; it never determines one. Fill it from your own AC 70/7460-1 evaluation.

Related Articles

  • Part 77 vs. TERPS — how the two surface systems differ and which governs an obstruction evaluation.