A runway threshold is the beginning of the portion of a runway that’s available for landing. It’s the precise point where a pilot is cleared to touch down, marked by a set of bold white stripes painted across the width of the pavement. Every runway has a threshold at each end, and its location determines how much landing distance is available, where lighting systems are positioned, and how obstacle clearance is calculated on approach.
How Threshold Markings Work
The most recognizable feature of a runway threshold is the set of parallel white stripes stretching across the pavement. These aren’t just decorative. The number of stripes tells pilots how wide the runway is. A 60-foot-wide runway has four stripes (two on each side of the centerline), while a 200-foot-wide runway has 16. Runways of widths in between follow a standardized scale published in the FAA’s Aeronautical Information Manual.
On runways used for instrument approaches, you’ll also find additional markings beyond the threshold: a touchdown zone marking and an aiming point. Both of these are referenced to the threshold’s position. The threshold essentially acts as the anchor point for the entire marking system on the landing side of a runway.
Threshold Lighting and Colors
At night or in low visibility, pilots identify the threshold by its green lights. A row of green lights faces outward from the runway end toward approaching aircraft, signaling “this is where you can land.” Those same light fixtures emit red light in the opposite direction, toward aircraft on the runway, to warn departing pilots they’re reaching the end of usable pavement. This dual-color design means one set of lights serves two purposes depending on which direction you’re looking from.
Many airports also install Runway End Identifier Lights (REILs), a pair of synchronized flashing lights placed on either side of the threshold. These help pilots quickly pick out the correct runway during approach, especially at airports surrounded by competing light sources from nearby roads or buildings.
Standard vs. Displaced Thresholds
Normally, the threshold sits at the very end of the paved runway surface. But sometimes an obstacle near the approach path, a hill, a building, or even construction equipment makes it unsafe to land at the very beginning of the pavement. In these cases, the threshold gets “displaced,” meaning it’s moved further down the runway.
A displaced threshold has distinct markings. White arrows run along the centerline leading up to the displaced threshold, and the threshold stripe itself is painted at the new, shifted location. The green threshold lights move to the displaced position too, so they no longer sit at the physical start of the pavement.
The area before a displaced threshold isn’t wasted. Aircraft can still use that pavement for takeoffs in either direction and for landings coming from the opposite end of the runway. They just can’t touch down on it when landing in the direction of the displacement. If the surface before the threshold is paved but truly unusable, it’s marked with chevrons (large painted arrows pointing toward the threshold) to warn pilots to stay off it entirely.
Why Thresholds Get Displaced
Permanent displacement typically happens because a fixed obstacle penetrates the approach surface, the imaginary slope that aircraft follow on their way down. If a building or terrain feature sits too close and too high near the runway’s end, moving the threshold further down the runway gives arriving aircraft the clearance they need to pass safely overhead.
Temporary displacement is common during construction. When work crews or equipment occupy part of a runway, the threshold shifts to keep landing aircraft away from the hazard. Pilots are notified through NOTAMs (Notices to Air Missions), which spell out exactly how far the threshold has moved and the revised distances available. A real-world example from Chicago O’Hare shows the format: “RWY 28 THR DISPLACED 1500FT,” followed by updated takeoff and landing distances for both directions of that runway.
How Thresholds Affect Landing Distance
The threshold directly determines a critical number called Landing Distance Available, or LDA. This is simply the length of runway from the threshold to the far end that a pilot can use for their ground roll after touchdown. When a threshold is displaced, LDA shrinks by the exact amount of the displacement. If a 13,000-foot runway has its threshold displaced by 1,500 feet, the LDA drops to 11,500 feet.
This matters for flight planning. Pilots calculate whether their aircraft can safely stop within the available distance given their speed, weight, weather conditions, and runway surface. A shorter LDA might force a heavier aircraft to divert to another airport or reduce its payload. Takeoff distances (measured from the runway’s physical start, not the threshold) are usually unaffected by a displaced threshold, which is why the pavement before it remains available for departures.
Obstacle Clearance and Approach Surfaces
The threshold also serves as the reference point for obstacle clearance on approach. International standards set by ICAO define an imaginary approach surface that begins a set distance from the threshold, typically 60 meters for most runway categories, and slopes upward and outward. Any object that pokes above this surface is considered an obstruction.
For precision approach runways (those equipped with electronic glide path guidance), the obstacle clearance height is calculated based on the threshold’s elevation above sea level, not the airport’s general elevation. This distinction matters when the threshold sits on a slope or at a different elevation than the rest of the airfield. Even a difference of more than 7 feet between the threshold and the airport’s published elevation triggers this separate calculation.
Risks of Misidentifying the Threshold
Landing before the threshold is one of the more dangerous errors a pilot can make, and it happens more often with displaced thresholds. The reason for the displacement, whether an obstacle or construction, means the pavement before the threshold was deemed unsafe for landing. Touching down early puts the aircraft in exactly the area it was supposed to avoid.
Displaced thresholds also create risks on takeoff. Pilots who don’t align properly with the runway centerline in the displaced area (which lacks centerline lights in many cases) can veer off course, damaging edge lights and scattering debris on the runway. Nighttime operations make this worse, since the visual cues in the displaced area are sparser than on the main runway. Pilots also need to be aware that a displaced threshold reduces their available stopping distance if they need to abort a landing and go around, since the missed approach surface is also referenced to the threshold location.