Requirement
Rule note
An ICAO Annex 14 equivalent is not yet incorporated into this calculator — select Project-Specific and enter your own criteria rather than assuming the FAA figures below apply.
Rule note
RCL is required for CAT II/III, and for CAT I when landing/takeoff RVR is below the thresholds entered below.
Required for CAT I when landing RVR < 2,400 ft (750 m as quoted in the AC).
Rule note
Required when takeoff RVR < 1,600 ft (480 m as quoted in the AC), unless an FAA-approved exception applies. These trigger values are FAA-based; ICAO Annex 14 uses different RVR thresholds (about 400 m for take-off), so confirm against your governing edition.
Rule note
Recommended (not required) for CAT I where runway width exceeds 170 ft. The AC rounds this to “50 m”, but 170 ft = 51.8 m and the calculator tests 170 ft exactly (ICAO uses 50 m). Entered in the length unit selected below.
Rule note
Recommended (not required) for CAT I where approach speed exceeds 140 kt.
Geometry & Spacing
Rule note
Threshold A to Threshold B (or the applicable calculation segment). Threshold A is treated as position 0. Colour zones are referenced to the runway end (stop end): where thresholds are displaced, enter the runway-end-to-runway-end length and set x₀ accordingly.
Rule note
Offset from Threshold A to the first generated centreline position, in the input unit above.
Rule note
FAA AC 150/5340-30J §3.3.1.1 — 50 ft (15.24 m). Edit only under Project-Specific basis. Always entered in metres regardless of the input unit above.
FAA — 2 ft (0.6096 m), kept unrounded internally.
Rule note
FAA — 2.5 ft (0.762 m) maximum uniform offset from the true centreline.
Rule note
FAA — 2 ft (0.6096 m) minimum clearance from a fixture base to a pavement joint, applicable to new runways.
FAA — final 1,000 ft (304.8 m).
Rule note
FAA — next 2,000 ft (609.6 m) toward the threshold. White occupies the remainder — never assume white is capped at a fixed 3,000 ft on runways longer than 6,000 ft.
Rule note
The exact first colour in the alternating sequence is figure/configuration-specific — this setting is exposed rather than hard-coded; confirm against the applicable FAA figure.
Existing-Installation Inspection (optional)
Rule note
Runs two checks: individual interval spacing against the ±tolerance above, and cumulative position against the theoretical design location x₀ + i·S — a sequence of uniform-but-off-nominal intervals can still drift out of tolerance cumulatively even if every individual interval passes.
Rule note
Checked against the calculated nominal fixture positions (or measured positions, if entered) — flags any fixture closer than the joint-clearance value above.
Inspection results
Report details
Colour & quantity schedule
Directional Colour Breakdown
Same physical fixtures, reclassified by landing direction. Totals match the physical fixture count in both columns — only the colour interpretation changes.
| Colour | Viewed from Threshold A (landing A→B) | Viewed from Threshold B (landing B→A) |
|---|---|---|
| White | — | — |
| Alternating (Red / White) | — | — |
| Red | — | — |
| Total (physical count) | — | — |
Centreline Light Quantity Summary
| Item | Quantity |
|---|---|
| Physical centreline fixtures (total) | — |
| Colour-zone lengths sum to runway length | — |
Calculated / Nominal Quantity — not a Final BOQ Quantity. Verify the exact zone-boundary and alternating-sequence endpoint arrangement against FAA Figure A-34 (or the applicable project figure) before issue.
Build-up
How This Calculator Works
Centreline colour zones are assigned from a single continuous position sequence, not calculated as three independent block counts — and colour is directional, so the same installed fixture is interpreted differently depending on which threshold a pilot is landing over.
Position generation before colour
Positions are generated first, at uniform spacing from the starting reference:
Only after the full position sequence exists is each position classified by colour. Calculating 3,000/2,000/1,000 ft zones independently and adding the counts can duplicate or omit a fixture at a zone boundary — this calculator avoids that by construction.
Colour-zone assignment (general form)
Measuring distance from the runway's stop end, general zone lengths (valid for any runway length, including short runways where the full 6,000 ft scheme cannot exist):
For L > 3,000 ft this is equivalent to: white until the last 3,000 ft, alternating for the next 2,000 ft, red for the final 1,000 ft — white is not capped at a fixed 3,000 ft on longer runways; it occupies the remainder.
Direction changes colour, not fixture count
Because the colour scheme is measured from the stop end in the landing direction, the same physical position is red when a small distance from Threshold B (landing A→B) but may be white when the same position is a large distance from Threshold A (landing B→A). This calculator keeps physical fixture count and optical colour interpretation as two separate outputs rather than conflating them.
Existing-installation inspection — two checks, not one
Individual interval spacing can each pass tolerance while the whole sequence still drifts from the intended layout. Both checks are run independently:
FAA AC 150/5340-30J §3.3.1.1 basis
| Parameter | Value |
|---|---|
| Longitudinal spacing | 50 ft (15.24 m) |
| Spacing tolerance | ±2 ft (0.6096 m) |
| Maximum lateral offset | 2.5 ft (0.762 m) |
| Pavement-joint clearance | 2 ft (0.6096 m) min. |
| White zone | Until final 3,000 ft |
| Alternating red/white | Next 2,000 ft |
| Red zone | Final 1,000 ft |
Independently confirm against the exact AC revision applicable to your project before relying on this as a standards reference.
Zone-length validation examples
| Runway L | Red | Alt. | White |
|---|---|---|---|
| 1,000 ft | 1,000 ft | 0 | 0 |
| 3,000 ft | 1,000 ft | 2,000 ft | 0 |
| 6,000 ft | 1,000 ft | 2,000 ft | 3,000 ft |
| 8,000 ft | 1,000 ft | 2,000 ft | 5,000 ft |
Requirement basis
| 🟢 Required | CAT II, CAT III; CAT I with landing RVR < 2,400 ft (750 m); takeoff RVR < 1,600 ft (480 m) (unless FAA exception) |
| 🟡 Recommended | CAT I with runway width > 170 ft (the AC quotes “50 m”; exact conversion ≈ 51.8 m), or approach speed > 140 kt |
| ⚪ Not required | Otherwise |
Quantity vs. serviceability
This calculator reports an installed fixture quantity, not a serviceability-adjusted count. Serviceability percentages by category belong in a separate AGL Serviceability Calculator, not multiplied into the quantity here.