Threshold

The threshold is the beginning of the portion of a runway that is available and suitable for landing. It is marked by a series of parallel white stripes (threshold markings) painted across the full width of the runway. The threshold is the zero point from which runway distances are measured.

Types of thresholds:

• Standard threshold: Located at the physical beginning of the runway pavement
• Displaced threshold: Located at a point beyond the physical start of the runway. The area before the displaced threshold (marked with white arrows) may be used for takeoff roll, rollout, and taxiing, but not for landing. Displacement is typically due to obstacles in the approach path, noise requirements, or pavement strength limitations
• Relocated threshold: Temporarily moved for construction, maintenance, or safety reasons

Threshold identification is enhanced at night by threshold lights — a row of green lights visible to approaching aircraft. The opposite end of the runway has red runway end lights.