What are threshold lights?
A transverse row of green lights marking the beginning of the part of the runway usable for landing.
The threshold marks the beginning of the portion of the runway available for landing. A transverse row of green lights spans the full runway width right at that point.
Threshold lights are fixed, unidirectional lights showing green in the direction of approach, so they are seen only by aircraft approaching that threshold. Wing bars, where provided, add at least five green lights on each side, extending at least 10 m outward from the line of the runway edge lights, for extra conspicuity.
Only where the threshold is at the runway extremity may the same row be a combined green/red bidirectional fixture, doing the job of the red runway end lights for aircraft using the runway from the opposite direction. Threshold lights are not runway end lights.
Frequently Asked Questions
Q1What are threshold lights?
A transverse row of green lights that marks the beginning of the part of the runway usable for landing, lying at right angles to the runway axis across the full runway width.
Q2What colour are threshold lights?
Green, as seen from the approach. They are fixed, unidirectional lights, so aircraft approaching that threshold see green and aircraft elsewhere do not see them.
Q3What is the spacing of threshold lights?
The row lies at right angles to the runway axis, as near the runway extremity as possible and not more than 3 m outside it. On a Category II or III precision approach runway the lights are uniformly spaced between the edge-light rows at not more than 3 m; on a Category I runway there are at least as many lights as 3 m spacing would give; on other runways the Annex sets a smaller minimum. Confirm against the current Annex 14 edition.
Q4How is threshold light intensity managed?
Intensity is adjustable and matched to the approach and runway lighting so the visual aids look balanced in the prevailing visibility and ambient light.
Q5Are threshold lights ever bidirectional?
Only where the threshold is at the runway extremity and the same fixtures also serve as runway end lights. They then show green to the approach and red toward the runway. Confirm the arrangement against Annex 14 and your State’s regulations.
Q6What is the difference between threshold lights and runway end lights?
Threshold lights are green and mark the beginning of the portion of the runway usable for landing. Runway end lights are red, face the runway, and mark the end of the usable runway.
Q7What happens to the lighting at a displaced threshold?
The threshold lights are placed at the displaced threshold. The runway edge lights between the start of the runway and the displaced threshold show red toward approaching aircraft (ICAO) and white in the opposite direction.
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