Extent, station/bar/fixture quantity, spacing, and toe-in tool for touchdown zone lighting (TDZL) — FAA AC 150/5340-30J and ICAO Annex 14 Vol. I.
Each longitudinal station is 2 transverse bars × 3 unidirectional lights — 6 physical fixtures per station, not per bar. Stations are generated from a fixed first-bar distance and nominal spacing, not from a blind length ÷ spacing division, so short-runway (half-length) extents are handled correctly. TDZL fixtures are unidirectional and face the landing threshold, so a runway lit for landing in both directions carries one complete set per landing direction; the calculator counts sets from the landing-direction selection. Requirement status is entered by the engineer and cross-checked against the approach category.
Selecting a standard loads its default first-bar distance, spacing and extent rule. Indian AAI / DGCA projects normally follow ICAO Annex 14 — select it for metric designs.
Select the status per the approved project specification. The calculator does not set it automatically, but it warns if "Not Required" or "To Be Determined" is chosen for a CAT II/III runway, where TDZL are normally provided (ICAO Annex 14 §5.3.14; FAA practice). FAA practice also calls for them on CAT I runways used for landing below RVR 2,400 ft (730 m), so enter the RVR to get that check.
Engineering basis: FAA imperial criterion — the 6,000 ft / 3,000 ft-extent boundary is always evaluated in feet internally, then converted to metres for display, to avoid rounding a boundary-adjacent length (e.g. 1,850 m) the wrong way.
Does not change the quantity. Under the FAA basis it checks that the outermost TDZL lights (46 ft / 14.0 m from centreline) lie within the pavement. Lateral positions are listed in the reference table below.
TDZL fixtures are unidirectional and face the landing threshold, so each lit landing direction has its own complete set in its own touchdown zone. Each set stops at the runway midpoint at most, so two sets never overlap.
FAA — 3 lights per bar (fixed). ICAO — not fewer than 3, not more than 1.5 m apart.
FAA — first bar 100 ft (30 m) from the landing threshold (displaced threshold, if any, to be confirmed against the approved drawing).
FAA permits the first bar at 100 ft ± 25 ft. Used by the inspection check only.
FAA — 4° ± 1° toward the runway centreline. A fixture-orientation requirement, not a quantity calculation.
FAA — 100 ft ± 2 ft between bars. ICAO — 30 m or 60 m (enter 98.43 ft or 196.85 ft).
FAA permits either method — this calculator does not prescribe the hardware approach.
| Component | Calculation Basis | Quantity |
|---|---|---|
| Longitudinal stations | First bar + uniform 100 ft spacing to extent | — |
| Transverse bars | 2 × stations | — |
| Individual light fixtures (one set) | lights per bar × bars (standard 3 × bars = 6 × stations) | — |
| Landing-direction sets | — | — |
| Calculated nominal total fixtures (all sets) | — |
Calculated / Nominal Quantity — not a Final BOQ Quantity. Lateral geometry, spares and any displaced-threshold layout must be confirmed against the approved drawing before issue.
Uses the first-bar distance, spacing and tolerances set on the Calculate tab, so enter those first.
Checks the first bar against the first-bar tolerance, each interval against the spacing tolerance, and the last station against the extent.
Compares an observed per-station fixture count against the expected 2 bars × lights per bar (6 for the standard 3-light bar).
TDZL quantity is generated from a station position sequence, then multiplied by a fixed per-station fixture count — not derived from a single runway-length division, which conflates bars with individual lights and mishandles short runways.
Evaluated in feet, never from a rounded metric value:
The FAA criterion is written as 6,000 ft (1,800 m), but 1,800 m is only 5,906 ft. The FAA basis therefore tests the boundary in feet; the ICAO basis tests it in metres (1,800 m). A runway of 1,800–1,828 m is thus a full-extent runway under ICAO and a half-extent runway under a strict FAA reading — pick the standard your project is governed by.
Stations are generated from the first-bar distance and nominal spacing, then bounded by the extent — never by dividing the extent by the spacing alone:
For the FAA configuration (Dfirst = S = 100 ft) a full 3,000 ft extent gives 30 stations. For ICAO (first pair 60 m, spacing 30 m, 900 m extent) it gives 29 pairs; at 60 m spacing it gives 15. If your layout starts the first pair at 30 m (30 m spacing), the same extent gives 30 pairs — confirm the first-pair distance against the approved drawing.
A transverse bar (ICAO: barrette) is not one fixture — it contains 3 unidirectional lights facing the landing threshold in the standard configuration, and each station has 2 bars (symmetrical about the centreline). ICAO permits more than 3 lights per barrette, so the calculator has a lights-per-bar input (fixed at 3 for FAA):
Reporting only bars (2N = 60 for the full configuration) understates the true fixture count by a factor of 3 — the individual-fixture figure (6N = 180) is what matters for BOQ, circuit loading, and transformer sizing.
TDZL fixtures are unidirectional and face the landing threshold. A runway lit for landing in both directions has one complete set in each touchdown zone, so the total is the per-set figure × 2. The two sets never overlap because each stops at or before the runway midpoint. Select a single threshold only where TDZL are provided for one landing direction.
| Parameter | Value |
|---|---|
| Rows | 2, symmetrical about centreline |
| Lights per bar | 3, unidirectional, white, 5 ft centres |
| Fixtures per station | 6 (2 × 3) |
| Inner light from centreline | 36 ft (72 ft gauge) |
| Light positions from centreline | 36, 41, 46 ft each side |
| First bar | 100 ft ± 25 ft from threshold |
| Bar spacing | 100 ft ± 2 ft |
| Full extent | 3,000 ft (L ≥ 6,000 ft) |
| Short-runway extent | ½ runway length (L < 6,000 ft) |
| Optical toe-in | 4° ± 1° toward centreline |
| Parameter | Value |
|---|---|
| Form | Pairs of barrettes, symmetrical about centreline |
| Lights per barrette | ≥ 3, not more than 1.5 m apart |
| Lateral gauge (innermost lights) | Equal to touchdown zone marking lateral spacing (18–22.5 m, 18 m preferred) |
| Colour / type | Fixed, unidirectional, variable white |
| Longitudinal spacing | 30 m or 60 m |
| Extent | 900 m (L ≥ 1,800 m), else not beyond midpoint |
| Provision | Shall: CAT II/III. CAT I: per authority / project decision |
Tolerances and positions should be confirmed against the exact AC / Annex 14 amendment applicable to your project before relying on this as a standards reference. First-pair distance for ICAO (60 m default) should be confirmed against the Annex 14 figure for your layout.
| Runway L | Extent | Stations | Bars | Fixtures |
|---|---|---|---|---|
| 6,000 ft | 3,000 ft | 30 | 60 | 180 |
| 5,000 ft | 2,500 ft | 25 | 50 | 150 |
| 4,000 ft | 2,000 ft | 20 | 40 | 120 |
| 2,400 ft | 1,200 ft | 12 | 24 | 72 |
| 3,000 m (ICAO, 30 m, first pair 60 m) | 900 m | 29 | 58 | 174 |
| 3,000 m (ICAO, 60 m, first pair 60 m) | 900 m | 15 | 30 | 90 |
This calculator collects approach category and RVR for documentation and asks the engineer to select the applicable requirement status directly, so the result is never presented as a computed standards citation. It does warn when CAT II/III is selected with TDZL marked "Not Required" or "To Be Determined", because TDZL are normally provided on those runways.
This calculator reports an installed fixture quantity, not a serviceability-adjusted count. Serviceability percentages belong in a separate AGL Serviceability Calculator, not multiplied into the quantity here.
Quick answers on how the calculator sizes touchdown zone lighting.
It works out the TDZL extent, the number of longitudinal stations, transverse bars and individual light fixtures, the spacing tolerance and the optical toe-in, using FAA AC 150/5340-30J or ICAO Annex 14 Vol. I. It also has an optional inspection check for measured station positions.
Each station has 2 transverse bars with 3 unidirectional lights each, so 6 fixtures per station. With N stations, the bar count is 2N and the fixture count is 6N. Stopping at the bar count is a common miscount that understates the fixtures by a factor of 3. ICAO allows more than 3 lights per barrette (not fewer than 3, not more than 1.5 m apart), so the calculator has a lights-per-bar input.
On the FAA basis the extent is 3,000 ft when the runway is 6,000 ft or longer, otherwise half the runway length. On the ICAO basis it is 900 m when the runway is 1,800 m or longer, otherwise not beyond the midpoint. The FAA boundary is tested in feet, and 1,800 m is only 5,906 ft, so runways of 1,800 to 1,828 m can fall on different sides of the boundary under the two standards.
Stations are generated from the first-bar distance and the nominal spacing, then bounded by the extent: N = floor((L_TDZ − D_first) ÷ S) + 1. For the FAA configuration (first bar and spacing both 100 ft) a full 3,000 ft extent gives 30 stations. For ICAO with the first pair at 60 m and a 900 m extent, 30 m spacing gives 29 pairs and 60 m spacing gives 15. Confirm the first-pair distance against the approved drawing.
Yes. TDZL fixtures are unidirectional and face the landing threshold, so each lit landing direction has its own complete set. The two sets never overlap because each stops at or before the runway midpoint. Select a single threshold only where TDZL are provided for one landing direction.
The first bar is at 100 ft ± 25 ft from the threshold and bars are spaced 100 ft ± 2 ft apart. The lights sit at 36, 41 and 46 ft each side of the centreline, and the optical toe-in is 4° ± 1° toward the centreline. Confirm tolerances against the exact AC or Annex 14 amendment that applies to your project.
No. The requirement status is selected by the engineer from the approved project specification, and the approach category and RVR are kept for documentation. The calculator warns if CAT II or CAT III is selected with TDZL marked Not Required or To Be Determined, because TDZL are normally provided on those runways.
No. It is a calculated nominal quantity of installed fixtures. Lateral geometry, spares, serviceability allowances and any displaced-threshold layout must be confirmed against the approved lighting layout drawing before issue.
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