Plain definitions of the terms that run through airport planning — design groups, safety and protection areas, imaginary surfaces, declared distances, and the FAA data products behind them. Each entry cites the governing Advisory Circular, Order, or regulation and links to the AvPlot tool that works with it. Definitions are reference summaries; the cited FAA document is the governing text. For the short A–Z abbreviation list, see the acronym quick reference.
Groups aircraft by approach speed — a letter A through E based on 1.3× the stall speed (VREF) in landing configuration. Category A is below 91 kt; Category E is 166 kt and above. The AAC combines with the Airplane Design Group and the approach visibility minimums to form a runway’s Runway Design Code, which selects the governing design standards.
Classifies aircraft by wingspan and tail height into Roman-numeral groups I through VI. Group I covers wingspans under 49 ft; Group VI covers 214 ft and above. Where wingspan and tail height fall in different groups, the more demanding group governs. ADG drives most lateral separation and clearance standards — object free areas, safety areas, and taxiway geometry.
Classifies aircraft by undercarriage geometry — Main Gear Width (MGW) and Cockpit-to-Main-Gear distance (CMG) — into groups 1A through 6. TDG governs taxiway and taxilane width, edge safety margin, shoulder width, and fillet design on curved segments. It is independent of the ADG: a single aircraft has both a wingspan-based ADG and a gear-based TDG.
The three-part code — AAC, ADG, and approach visibility minimums — that identifies which row of the design-standards tables governs a runway (for example, C-III-2400). It signals the design intent for the runway; the related Runway Reference Code (RRC) reflects current operating capability. The RDC is the entry key into nearly every dimensional standard in the AC.
The graded, cleared, and drained surface surrounding the runway, built to support an aircraft during an undershoot, overshoot, or excursion without structural damage. It must be free of objects except those fixed by function. RSA length and width are set by the Runway Design Code via the design-standards matrix — not a single fixed value.
A ground area centered on the runway and its extended centerline that must be clear of above-ground objects, except those fixed by function (such as NAVAIDs that must sit there). The ROFA is wider and longer than the RSA it encloses. Its dimensions come from the design-standards matrix keyed to the Runway Design Code.
The core component of the Obstacle Free Zone: a volume of airspace centered on the runway centerline and extending a short distance beyond each end, which must remain clear of all objects except frangible NAVAIDs fixed by function. It protects aircraft operating close to the runway surface during low-altitude flight.
The airspace above the runway and its immediate approaches that must be kept clear to protect low-altitude operations. It comprises the runway OFZ (ROFZ) plus, where applicable, inner-approach and inner-transitional OFZ sub-surfaces. Only frangible visual NAVAIDs that must be located there may penetrate it.
A volume just beyond the runway threshold that must be kept clear when a vertically guided approach is in use and the ceiling is below 250 ft or visibility below ¾ statute mile. It protects an aircraft on short final from obstacles near the threshold during the most demanding approach conditions.
A trapezoidal area on the ground off the runway end whose function is to protect people and property by controlling land use. Approach RPZs begin 200 ft before the threshold; departure RPZs anchor to the takeoff-run (TORA) end. RPZ size is set by the approaching aircraft’s AAC and the approach visibility minimums; AvPlot fetches the controlling dimensions from the design-standards data rather than hardcoding them.
The federal regulation establishing the imaginary surfaces — primary, approach, transitional, horizontal, and conical — used to identify objects that may be obstructions to the navigable airspace around an airport, and the notice requirements for proposed construction. The civil-airport imaginary surfaces are defined in §77.19; the approach surface anchors 200 ft beyond the threshold.
A sloped evaluation surface used in instrument procedure design under TERPS. If an obstacle penetrates the OCS, the procedure’s minimums must be raised or the design adjusted. AvPlot evaluates OCS penetrations alongside the Part 77 surfaces in its obstruction analysis. Distinct from Part 77: the OCS governs instrument-procedure design, not airspace obstruction screening.
The U.S. Standard for Terminal Instrument Procedures (FAA Order 8260.3) — the criteria set for designing instrument approach and departure procedures. It defines the Obstacle Clearance Surfaces evaluated when establishing approach minimums. TERPS surfaces are distinct from the Part 77 imaginary surfaces: Part 77 screens obstructions to airspace; TERPS sets what an instrument procedure can achieve.
A single latitude/longitude marking the approximate geometric center of an airport’s usable runways — the official location of the airport for charting and data purposes. It is typically computed as the length-weighted centroid of the runway ends. (In FAA organizational shorthand, ARP also names the Office of Airports.)
The four published runway lengths an operator may use: TORA (Takeoff Run Available), TODA (Takeoff Distance Available — TORA plus any clearway), ASDA (Accelerate-Stop Distance Available — TORA plus any stopway), and LDA (Landing Distance Available). They let an airport credit or debit usable length for clearways, stopways, and displaced thresholds. In AvPlot the departure RPZ anchors to the TORA end.
The FAA’s authoritative subscription of airport, runway, and NAVAID data, refreshed on the 28-day aeronautical data cycle. It is AvPlot’s primary source for U.S. airport facts — identifiers, reference points, elevations, runway dimensions, declared distances, and NAVAIDs — and every record carries its cycle date so citations stay traceable.
The set of tables in AC 150/5300-13B Appendix G giving runway design standards — safety areas, object free areas, protection zones, separations, and holding positions — indexed by design group and approach visibility. It is the authoritative source behind AvPlot’s reference endpoints: the tools fetch dimensions from it rather than restating values in the frontend.
The facility from which controllers manage aircraft on the airport surface and in the local airspace. Tower siting requires an unobstructed line of sight to the runways, taxiways, and approach areas controllers must observe; FAA Order 6480.4C governs the siting and line-of-sight analysis. AvPlot’s ATCT tool evaluates visibility and shadowing from a candidate cab location.
The FAA-approved, scaled drawing set depicting an airport’s existing and planned facilities. A current ALP is a prerequisite for federally funded development, and its standardized data tables are reviewed under FAA Office of Airports procedures. AvPlot generates ALP data tables aligned to those standards.
The FAA’s biennial inventory of airports significant to national air transportation. Inclusion establishes eligibility for Airport Improvement Program (AIP) funding and assigns each airport a service level and hub category. These classifications are not carried in NASR; AvPlot joins them from the published NPIAS report.
The FAA’s official forecast of aviation activity — operations, based aircraft, and enplanements — for U.S. airports, published annually. Planner-developed forecasts are checked for consistency against the TAF as part of FAA forecast approval. Not to be confused with the weather Terminal Aerodrome Forecast, which shares the acronym.
The multi-year schedule of an airport’s planned capital projects with their estimated costs and funding sources, typically an output of the master plan. The FAA maintains a parallel Airport Capital Improvement Plan (ACIP) used to prioritize AIP funding. The CIP turns planning recommendations into a phased, budgeted roadmap.
In the airport-planning context, an FAA Office of Airports (ARP) Standard Operating Procedure — the internal review standard for a deliverable. ARP SOP 2.00 governs ALP review; ARP SOP 3.00 governs the Exhibit ‘A’ property inventory map. AvPlot’s ALP and Exhibit ‘A’ outputs are structured to match these review standards.
Definitions are reference summaries for planning use, not a substitute for the governing FAA text or for stamped engineering. Where a citation gives a paragraph or table number, it refers to AC 150/5300-13B (Airport Design) Change 1 unless another document is named. Looking for a specific tool? See the AvPlot toolkit or the acronym quick reference.