Taxiway Geometry · Design Groups

Taxiway Design: Fillet Geometry and Separation Standards

By AvPlot Team Published June 2026 9 min read

The single most useful thing to know about taxiway design under AC 150/5300-13B is that it runs on two different design groups, not one. Separation standards key to the Airplane Design Group (ADG) — a wingspan band — while width and fillet geometry key to the Taxiway Design Group (TDG) — a landing-gear-geometry band. Mix them up and you size a taxiway against the wrong table. This article keeps them straight and walks the fillet and separation workflow a consultant uses to design a taxiway improvement.

Two design groups, two jobs

Both groups come from the design aircraft, but they describe different physical realities and drive different standards.

ADG — Airplane Design Group. A band of wingspan (and tail height). Because it is about how much room the wingtips sweep, the ADG drives separation: runway-to-taxiway centerline, taxiway-to-taxiway, taxiway/taxilane to a fixed or movable object, and the taxiway object free area (TOFA). ADG ranges: I <49 ft, II 49–79 ft, III 79–118 ft, IV 118–171 ft, V 171–214 ft, VI ≥214 ft.
TDG — Taxiway Design Group. A band defined by the main gear width (MGW) and the cockpit-to-main-gear distance (CMG). Because it is about how the gear tracks through a turn, the TDG drives pavement width, taxiway edge safety margin (TESM), shoulder width, and fillet geometry.

Source: AC 150/5300-13B Change 1 — ADG and TDG definitions; the TDG classification ranges are in Table 1-4 (p. 1-15).

Two failure modes follow directly. Designing separation off the TDG, or designing pavement width off the ADG, both produce a noncompliant taxiway that looks reasonable on paper. The discipline is: separation → ADG, geometry → TDG.

Separation: keyed to ADG

The taxiway separation standards — runway centerline to parallel taxiway centerline, taxiway centerline to taxiway/taxilane centerline, and taxiway/taxilane centerline to a fixed or movable object — are all read from the design tables by ADG (and, for the runway-to-taxiway case, by the runway’s approach visibility as well). These are not values to carry over from a prior plan; they come straight from the current standards table.

Source: AC 150/5300-13B Change 1, Table 4-1 — taxiway/taxilane separation standards keyed by ADG. (AvPlot keys these by ADG per Table 4-1, not by TDG.)

Width and shoulders: keyed to TDG

Taxiway pavement width, the taxiway edge safety margin (the distance from the outer main gear to the pavement edge), and shoulder width are fixed by TDG and are constant per the AC — safe to read from the table directly.

Taxiway width / TESM / shoulder by TDG (AC 13B Table 4-2)
TDG	Taxiway width	TESM	Shoulder width
1A / 1B	25 ft	5 ft	10 ft
2A / 2B	35 ft	7.5 ft	15 ft
3 / 4	50 ft	10 ft	20 ft
5 / 6	75 ft	14 ft	30 ft (40 ft for four-engine TDG 6)

Source: AC 150/5300-13B Table 4-2 — taxiway width, TESM, and shoulder width by Taxiway Design Group.

Fillet geometry: where the gear tracks the turn

A taxiway fillet is the extra pavement at an intersection that keeps the main gear on the paved surface while the pilot keeps the cockpit over the centerline through the turn. Because larger, longer-wheelbase aircraft cut the corner more sharply, fillet geometry is a TDG problem, and it is solved in Appendix J.

What drives a fillet

TDG — sets the CMG and MGW that define how the gear tracks.
Turn (intersection) angle — the delta between the two taxiway legs. Sharper turns demand more fillet.
Centerline turn radius (R-CL) and fillet radius (R-Fillet) — the design radii the fillet is built around.

Two regimes by turn angle

The Appendix J behavior splits at the turn angle:

Delta ≤ 90°: the R-Fillet is 0 ft — no separate fillet radius is required — and the minimum R-CL is fixed per TDG (1A/1B/2A = 50 ft, 2B/3 = 75 ft, 4/5 = 110 ft, 6 = 150 ft).
Delta ≥ 120°: R-Fillet defaults follow Tables J-1..J-8 (e.g., 1A = 0, 1B = 20, 2A/2B = 50, 3 = 25, 4/5/6 = 50 ft).

The taper design (the W/L dimensions that shape the fillet) is read verbatim from the published Tables J-1..J-8 when the exact (TDG, delta, R-CL, R-Fillet) combination is tabulated, and otherwise synthesized from the App J.2.11 swept-envelope method.

Source: AC 150/5300-13B Change 1, Appendix J (Tables J-1..J-8) — fillet design by TDG, turn angle, R-CL, and R-Fillet. Change 1 (8/16/2024) replaced the 2022 Figure 1-1 diagonal TDG boundaries with the Table 1-4 rectangular ranges.

Designing a taxiway improvement — the order of operations

Identify the design aircraft and read off both its ADG (wingspan) and its TDG (MGW + CMG).
Set separation from the ADG: confirm runway-to-taxiway and taxiway-to-taxiway/object distances against Table 4-1.
Set the cross-section from the TDG: width, TESM, and shoulders from Table 4-2.
Design each intersection from the TDG and the turn angle: R-CL, R-Fillet, and the Appendix J taper.
Check the result against the taxiway/taxilane object free area and against the runway environment it ties into.

Keep the two groups in their lanes and the design is internally consistent: the aircraft fits between things (ADG) and fits on the pavement through every turn (TDG).

Try it in AvPlot

Generate fillet geometry and check separation

The Taxiway Fillet tool builds the Appendix J fillet for a TDG, turn angle, and radii; the Taxiway Separation tool returns the ADG-keyed separation standards — both with the citation trail attached.

Open Taxiway Fillet →

This article is a reference summary for planning use, not a substitute for the governing FAA text. Citations refer to AC 150/5300-13B Change 1 (Airport Design) — Table 1-4 (TDG classification), Table 4-1 (separation), Table 4-2 (taxiway width), and Appendix J (fillet design, Tables J-1..J-8). Change 1 is effective August 16, 2024. Always verify dimensions against the current governing documents and your FAA regional office before issuing a design product. See the full airport planning glossary or the AvPlot toolkit.