How do threshold and displaced threshold markings and lights work together?
By day the paint shows where landing begins, and at night the lights show the same place. When the threshold is displaced, both move to the new position, and the pavement behind them is marked and lit as not for landing.
The threshold is the start of the part of the runway available for landing. It is shown twice, at the same place: as paint for daylight and as lights for night and low visibility. A displaced threshold keeps that pairing and simply moves it down the runway.
1The standard threshold
The marking is a set of white longitudinal stripes, placed symmetrically about the centreline just inside the runway start, with the runway number after them. The number of stripes depends on the runway width. The lights are a row of green lights across the full width of the runway at the threshold, and, where wing bars are provided, a wing bar of green lights on each side in line with it. Wing bars add conspicuity and are not fitted on every runway. Both marking and lights give the same position.
2The displaced threshold: the marking
A white transverse bar across the runway marks the displaced position, added in front of the normal threshold stripes with the runway number after them, and white arrows along the centreline in the area before it point toward the bar. The arrows are the daylight warning: the pavement behind them is there, but a pilot on approach must not land on it. This is the ICAO arrangement; other authorities, such as the FAA, may mark a displaced threshold with the bar and arrows only.
3The displaced threshold: the lights
The green threshold lights and wing bars move to the displaced position. The runway edge lights in the displaced area show red to the approach and white the other way. The pilot reads red edge lights, then green where landing begins, so the lights say what the arrows say.
4What moves and what stays
Everything set out from the landing threshold follows it: the approach lights, the PAPI and the touchdown zone lights. The runway end lights stay at the physical end of the runway. The displaced area is normally still usable for taxiing, take-off and the roll-out of aircraft landing from the opposite direction, and the landing distance available is shorter by the displacement.
5Keeping the two in step
The paint and the lights are set out from the same survey point. After resurfacing, repainting, a change of displacement or temporary works, they are checked against each other. A bar marked at one position and green lights at another would give a pilot two different thresholds, which is a defect to fix.
| Feature | Standard threshold | Displaced threshold |
|---|---|---|
| Marking | White longitudinal stripes, then the runway number | White transverse bar and threshold stripes at the displaced position, arrows on the centreline before it |
| Threshold lights | Green, across the runway at the threshold | Green, across the runway at the displaced position |
| Wing bars | Green, each side of the threshold | Green, each side of the displaced position |
| Edge lights before the threshold | Not applicable | Red to the approach, white the other way |
| Approach lights, PAPI, TDZ lights | Set out from the threshold | Set out from the displaced threshold |
| Runway end lights | At the runway end | Stay at the physical runway end |
| Landing begins | At the threshold | At the displaced threshold |
Frequently Asked Questions
Q1Why does the threshold have both a marking and lights?
They say the same thing in two forms. The paint is read by day and the lights by night and in low visibility, and both are set out from the same survey point so they agree on where landing begins. If one is worn, hidden or switched off, the other still shows the threshold.
Q2How do I recognise a displaced threshold by day?
By a white transverse bar across the runway at the displaced position, with the threshold stripes after it, and white arrows along the centreline in the area before it. The arrows lead toward the bar, so the paint itself tells a pilot that landing begins farther along.
Q3What do the lights show at a displaced threshold?
To a pilot on approach, the runway edge lights in the displaced area show red, and the threshold lights across the runway at the displaced position show green, with wing bars beside them. The pilot reads the sequence directly: red, then green where landing begins.
Q4Can aircraft use the pavement before a displaced threshold?
Normally it can be used for taxiing, take-off, and the landing roll-out of aircraft arriving from the opposite direction, but not for landing on the approach side. Whether it can be used, and for what, is published with the declared distances, and it can be closed to some uses.
Q5Do the approach lights and PAPI move with a displaced threshold?
Yes. Everything set out from the landing threshold follows it: the approach lighting, the visual approach slope indicator and the touchdown zone lights. The runway end lights do not move and stay at the physical end of the runway.
Q6Are the markings and lights always checked together?
They should be. After resurfacing, repainting, a change of displacement or temporary works, the paint and the lights are checked against each other so that both show the same threshold. A mismatch, such as a green bar at one position and a marking at another, is a defect to fix.
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