Displaced Threshold – Aviation Glossary

Definition and Core Concept

A displaced threshold is a runway threshold positioned at a point other than the physical beginning of the runway pavement. Unlike a standard threshold, which marks where aircraft are permitted to land from the approach direction, a displaced threshold designates a new, advanced touchdown point along the runway. The runway area prior to this threshold cannot be used for landing from that direction, but remains available for takeoff, landing rollout in the opposite direction, and taxi operations.

Displaced thresholds are implemented according to ICAO Annex 14 and FAA guidelines to satisfy requirements regarding obstacle clearance, pavement strength, environmental constraints, and noise abatement. They are marked with distinctive white arrows, arrowheads, and a broad threshold bar, with green threshold lights for night or low-visibility operations. The displaced threshold is depicted on airport diagrams, approach plates, and reflected in declared runway distances.

This operational design allows airports to maximize available runway for takeoff and rollout without compromising landing safety. Displaced thresholds may be permanent—addressing unchangeable factors like terrain or obstacles—or temporary, during construction or repairs. Understanding their use is essential for pilots, air traffic controllers, airport operators, and anyone involved in airport operations.

Purpose and Operational Context

Displaced thresholds are engineered elements of airport design, introduced when the runway end closest to the approach direction is unsuitable for landing. Their uses include:

• Obstacle Clearance: To ensure arriving aircraft clear obstacles (buildings, trees, roads) on final approach, the threshold is moved further down the runway.
• Runway Surface Preservation: The initial runway segment may not be strong enough for repeated landing impacts, due to construction, age, or repair needs.
• Noise Abatement: By moving the touchdown point farther from populated areas, aircraft stay higher over noise-sensitive zones, reducing ground-level noise.
• Environmental Compliance: Displacements may help protect wetlands, wildlife habitats, or historical sites adjacent to runways.
• Temporary Operations: During maintenance or construction, a temporary displaced threshold may be used to allow continued safe operations.

Displaced thresholds are a dynamic, regulatory-driven adaptation of runway operations, supporting safety, regulatory compliance, and operational efficiency.

Visual Identification and Markings

Displaced thresholds feature distinctive markings and lighting, standardized worldwide:

• Runway Markings: The pavement before the threshold is marked with a series of large white arrows pointing to the new threshold. Just before the threshold bar, broad arrowheads span the runway width. The threshold itself is marked by a thick, solid white line (threshold bar) across the runway, followed by standard threshold markings (parallel white bars) for the touchdown zone.
• Lighting: Green threshold lights are positioned at the new threshold for night/low-visibility. Original threshold lights are relocated as needed.
• Signage: Runway distance remaining signs are recalibrated to reflect the new landing distance.

These markings ensure that the displaced threshold is unmistakable, reducing the risk of landing errors.

Operational Rules and Permitted Uses

Each runway segment—before and after the displaced threshold—has specific allowed uses, strictly enforced for safety:

Landing on the area before a displaced threshold is strictly prohibited from the approach direction, except in emergencies. Takeoffs, taxiing, and rollout from the opposite direction are permitted.

Regulatory and Practical Reasons

Displaced thresholds are mandated or recommended for several main reasons:

• Obstacle Clearance: ICAO and FAA rules require sufficient vertical clearance over obstacles. If an obstacle penetrates the required approach surface, the threshold is displaced.
• Pavement Strength: The runway’s initial segment may not be rated for landing forces but is acceptable for takeoff and taxi loads.
• Noise Abatement: Community or regulatory requirements may call for displaced thresholds to reduce noise over residential areas.
• Runway Maintenance: Temporary displacements allow continued safe operations during repairs or construction.
• Environmental Protection: Displacements may be required to protect wetlands or sensitive habitats.

The position and duration of a displaced threshold are determined by airport engineers, authorities, and operational stakeholders.

Types: Permanent vs. Temporary

• Permanent Displaced Thresholds: Address long-term issues such as persistent obstacles, pavement design limits, or environmental constraints. Incorporated into permanent airport documentation and charts.
• Temporary Displaced Thresholds: Used during short-term issues like runway repairs, construction, or temporary obstacles. Announced via NOTAMs and removed when the issue is resolved.

Temporary displacements require heightened pilot awareness and up-to-date information.

Declared Distances and Instrument Approach Effects

Displaced thresholds directly change runway declared distances:

• Takeoff Run Available (TORA): Usually includes the full runway, as the displaced area is available for takeoff.
• Landing Distance Available (LDA): Begins at the displaced threshold and excludes the area before it.
• Accelerate-Stop Distance Available (ASDA): Typically matches TORA unless restrictions apply.

All instrument approach procedures reference the displaced threshold for touchdown, and charts reflect the revised LDA.

Practical Examples

• Obstacle Clearance: A threshold is displaced 700 feet to clear tall trees near the approach path.
• Pavement Preservation: 500 feet of cracked pavement at the runway start are excluded from landing, but used for takeoff/taxi.
• Temporary Construction: 1,200 feet are closed for resurfacing; a temporary threshold is established and published via NOTAM.
• Instrument Approach: Charts show the displaced threshold and adjusted landing distances for pilots to use in flight planning.

Common Pilot Questions

• Why can’t aircraft land before a displaced threshold?
  The pavement may not handle landing stresses, or obstacle clearance may not be met. Only takeoff, taxi, or rollout from the opposite direction are allowed.

• What if a pilot lands before the displaced threshold?
  This is a regulatory violation (except in emergencies) and may trigger an investigation.

• How do pilots find displaced threshold information?
  On airport diagrams, approach plates, and in NOTAMs for temporary thresholds.

• Does the displaced area count for landing distance?
  No, only the pavement beyond the threshold bar is counted as LDA.

Related Terms

• Runway Threshold: Beginning of the usable landing portion of a runway.
• Touchdown Zone (TDZ): First 3,000 feet (or first third) beyond the threshold.
• Blast Pad/Stopway: Specially marked areas not suitable for landing, often beyond the runway end.
• Declared Distances: Officially published runway lengths for takeoff, landing, and safety planning.
• Instrument Approach: A procedure guiding aircraft to a runway, referencing the displaced threshold for touchdown.

A displaced threshold is a vital safety, regulatory, and operational tool in modern airport management, ensuring safe, flexible, and community-conscious runway use worldwide.