Runway Threshold – Comprehensive Aviation Glossary

Definition

A runway threshold is the precise point on a runway where the certified landing surface begins, playing a critical role in safe airport and flight operations. Its location is established by considering obstacles, pavement strength, and operational needs, and it is indicated by internationally standardized markings and lighting. According to ICAO Annex 14, the threshold is “the beginning of that portion of the runway usable for landing.” A threshold’s placement and type directly impact available landing and takeoff distances, making its accurate identification essential for pilots, ground staff, and air traffic controllers.

Types of Runway Thresholds

Standard Threshold

A standard threshold is at the physical beginning of the runway. The entire paved surface is available for landing and takeoff. This configuration maximizes usable runway length and is preferred whenever possible.

Displaced Threshold

A displaced threshold is positioned further down the runway. The area before the threshold is not suitable for landing, often due to approach obstacles, insufficient pavement strength, or noise abatement. However, this pre-threshold area may be used for takeoff or for rollout after landing from the opposite direction. Displaced thresholds are marked with white arrows on the pavement and a threshold bar at the landing surface start.

Relocated Threshold

A relocated threshold is moved down the runway, typically due to construction, repairs, or hazards. The area before it is closed to all aircraft operations. Markings include white arrows guiding to the new threshold and yellow Xs on the closed area, with lighting and signage updated accordingly.

Visual Identification: Markings and Lighting

Threshold Markings (“Piano Keys”)

Thresholds are marked by a series of thick, longitudinal white stripes (“piano keys”) across the runway width. The number of stripes is proportional to runway width, aiding pilots in identifying the threshold and the runway’s size. For example, a 150 ft (45 m) wide runway displays 12 stripes.

Immediately beyond the stripes is the threshold bar—a solid white bar at least 10 ft (3 m) wide, spanning the runway. This marks the exact start of the usable landing area.

Displaced and Relocated Threshold Markings

• Displaced threshold: White arrows along the centerline point toward the threshold, with a row of arrowheads just before the threshold bar.
• Relocated threshold: White arrows and yellow Xs (each at least 20 ft/6 m high) mark the closed area, with the new threshold bar at the relocated point.

Lighting

Thresholds are lit with a continuous row of green lights visible from the approach direction, and red from the opposite direction. Runway End Identifier Lights (REILs)—flashing white lights—may flank the threshold, increasing visibility at night or in low visibility. All lighting is maintained to the highest operational standards, with any outages reported immediately via NOTAM.

Marking Dimensions and Standards

• Each stripe: 150 ft (45.7 m) long, 5.75 ft (1.75 m) wide.
• Threshold bar: minimum 10 ft (3 m) wide, full runway width.
• Markings are always white on runways.
• Displaced/relocated thresholds: additional white arrows, arrowheads, and yellow Xs as appropriate.

Associated Runway Areas

• Blast Pad/Stopway/Overrun: Marked with yellow chevrons, not for normal operations. Provides a buffer in case of overruns.
• Runway Safety Area (RSA): Cleared, graded zone beyond the threshold for aircraft undershoot/overshoot recovery.

Operational Use Cases

Pilot Procedures

Landing:
Pilots use the threshold as the touchdown reference. For standard thresholds, landing may occur anywhere after the bar. For displaced thresholds, pilots must not land before the bar; for relocated thresholds, the area before is entirely off-limits.

Takeoff:
The area before a displaced threshold can be used for takeoff roll, but not for landing. Before a relocated threshold, no operations are permitted.

Rollout:
Landing from the opposite direction, the pre-threshold area of a displaced threshold may be used for rollout.

Airport Operations and Ground Staff

Ground staff ensure markings and lighting are maintained, especially after threshold changes. They apply correct markings (arrows, bars, Xs), update signage, and ensure obsolete lighting is removed or covered. All changes are communicated via NOTAMs and airport diagrams.

Air Traffic Control (ATC) and Dispatch

ATC relays current threshold configurations to pilots via ATIS, NOTAMs, and direct communication. Dispatchers must account for changed runway lengths in flight planning.

Regulatory and Safety Considerations

All threshold markings and lighting comply with:

• ICAO Annex 14, Volume I (global standard)
• FAA AC 150/5340-1M (U.S. standard)
• ICAO Doc 4444 (ATC procedures)
• State/Local Requirements as applicable

Markings must be white, clean, and highly visible; lights must be operational in all conditions. Threshold changes are always published in NOTAMs and reflected in current charts.

Safety Implications

Correct threshold identification is critical. Landing before the threshold bar can cause accidents, as with Comair Flight 5191 (Lexington, KY, 2006), where misidentification led to a fatal crash. Instrument approaches are calibrated to the threshold, making its accuracy essential for safe operations.

Best Practice Checklist

Glossary of Key Terms

Use Case Examples

Landing with a Displaced Threshold

Example:
San Diego International (SAN) RWY 27 uses a 1,810 ft displaced threshold. Aircraft must touch down after the threshold bar, not before, due to approach obstacles. The pre-threshold area can be used for takeoff or opposite-direction rollout.

Temporary Threshold Relocation

Example:
During construction, a runway threshold is relocated 2,000 ft down. White arrows and a new threshold bar are marked; yellow Xs close the old area. Only the relocated threshold is available for landing and takeoff.

Night Operations

Pilots rely on green threshold lights and REILs to identify the runway start. Proper lighting and markings are essential for safe night/instrument operations.

Summary Table: Threshold Types and Uses

References

• ICAO Annex 14, Volume I – Aerodrome Design and Operations
• FAA AC 150/5340-1M – Standards for Airport Markings
• ICAO Doc 4444 – Air Traffic Management
• NTSB Accident Report: Comair Flight 5191

Runway thresholds are essential components of airport safety and efficiency, providing standardized cues that ensure every landing and takeoff occurs on certified, obstacle-free pavement. Maintaining and correctly identifying these markings and lights is a shared responsibility of pilots, ground staff, and controllers—critical to preventing accidents and optimizing operational capacity.