Hold Crossing Light (HCL) – Airport Lighting Glossary

Definition and Core Function

Hold Crossing Lights (HCLs) are advanced, in-pavement red lighting arrays installed where taxiways intersect runways at airports. These lights provide a high-visibility, automated warning to pilots and ground vehicle operators that it is unsafe to enter or cross an active runway. When illuminated, HCLs serve as an unambiguous “stop” signal, supplementing Air Traffic Control (ATC) instructions and reducing the risk of runway incursions.

Where Are HCLs Used?

HCLs are primarily found at major commercial airports with complex taxiway/runway layouts, high traffic volumes, or a history of runway incursions. The International Civil Aviation Organization (ICAO) recommends their use at aerodromes with frequent runway crossings or elevated incursion risk, especially under low visibility conditions. In the United States, HCLs are a key element of the FAA’s Runway Status Lights (RWSL) program.

How Do HCLs Operate?

HCLs are integrated with airport surface surveillance systems—such as ASDE-X (Airport Surface Detection Equipment, Model X) and ASSC (Airport Surface Surveillance Capability). These systems track real-time positions and movements of aircraft and vehicles. When the system’s logic detects that a runway is or soon will be unsafe to cross, it automatically illuminates the HCLs. Notably, HCLs operate independently from ATC; controllers cannot override or control these lights, ensuring a robust fail-safe layer against human error or miscommunication.

Why Are HCLs Important?

Runway incursions are among the most significant risks in airport operations. HCLs provide a direct, visual “last line of defense” by alerting crews and drivers to stop before entering a potentially hazardous runway. Their role is especially critical during periods of low visibility or high operational workload, where traditional cues might be missed.

Purpose and Safety Role in Airport Operations

Preventing Runway Incursions

HCLs are a vital component of a layered airport safety system. They provide real-time, automated surface status information that supplements ATC clearances and visual observation. Both ICAO and FAA standards identify HCLs as essential at airports with heavy runway crossing traffic or recurring visibility issues.

Operational Benefits

HCLs enhance safety and efficiency by:

• Preventing runway incursions: Automated activation means HCLs illuminate precisely when a runway crossing is unsafe, regardless of possible ATC clearance errors.
• Enhancing situational awareness: The conspicuous red lights are unmistakable, especially during complex taxiing, at night, or in fog.
• Supporting ATC workload: By automating a critical safety warning, HCLs reduce controller workload and provide a redundant safety check.
• Reducing delays and incidents: By preventing last-second aborts or missed approaches, HCLs help maintain smooth airport operations.

Who Relies on HCLs?

• Pilots: Use HCLs as part of their taxi and crossing procedures.
• Ground vehicle operators: Rely on HCLs for safe movement across runways.
• ATC: Benefit from an added, independent safety measure.

Regulatory Guidance

Both ICAO and the FAA emphasize that HCLs do not replace the requirement for ATC clearance to enter or cross a runway. If a discrepancy exists between HCLs and ATC instructions, operators must stop and notify ATC.

System Description and Operating Logic

Physical Layout and Components

HCLs are flush-mounted, unidirectional red light fixtures embedded in the pavement at taxiway/runway intersections, aligned with painted hold short lines. Additional fixtures may extend the warning along the runway centerline.

Lighting Technology

Most HCLs use LEDs, offering high brightness, low power draw, and long life. Fixtures are unidirectional, focusing the red light toward approaching traffic at the hold line.

Control and Automation

HCLs are not operated by ATC. Their activation is automated, based on real-time data from surface surveillance systems. The RWSL processor uses algorithms to predict hazardous situations and illuminate HCLs accordingly.

Activation Logic

• Red Lights On: When a runway is, or will soon be, occupied by a fast-moving aircraft or vehicle, HCLs illuminate at all affected intersections.
• Red Lights Off: When the hazard has passed and the runway is clear, HCLs extinguish—but this does not constitute clearance.

Integration with Other Systems

HCLs are part of the broader RWSL suite, which also includes Runway Entrance Lights (RELs) and Takeoff Hold Lights (THLs), creating a comprehensive, automated runway safety system.

Technical Specifications

Color and Visibility

HCLs emit a steady, bright red light, universally recognized in aviation as “stop/prohibited.” Intensity is adjustable for different ambient conditions.

Fixture Design

Designed for flush, in-pavement installation, HCLs withstand heavy aircraft and vehicle loads. LEDs are preferred for their longevity and reliability.

Spacing and Orientation

HCLs are spaced 10–20 feet apart across the taxiway, starting at the runway holding position and extending to the edge. Extra fixtures may be installed at the runway centerline.

Surveillance Data Integration

System logic depends on continuous, accurate data from ASDE-X or ASSC, using radar, multilateration, and transponder signals to track all surface movements.

Environmental and Maintenance Factors

Fixtures are sealed against water and debris, often heated in cold climates. Automated diagnostics alert maintenance teams of any faults.

Operating Characteristics

Typical Movement Sequences

Departures:

1. Aircraft ready for takeoff triggers HCLs to illuminate at all intersecting taxiways ahead.
2. As the aircraft passes each intersection, HCLs extinguish in real time.
3. When the runway is clear, all HCLs turn off.

Arrivals:

1. Aircraft on final approach triggers HCLs at all intersections.
2. As the aircraft lands and decelerates, HCLs at each intersection extinguish as it passes.
3. Once the aircraft has exited and the runway is clear, HCLs turn off.

Handling Multiple Movements

The system dynamically recalculates risk, illuminating HCLs as needed for simultaneous arrivals, departures, or vehicle crossings.

Automation and ATC Interaction

ATC cannot override HCLs. Pilots and drivers must stop at illuminated HCLs, even if cleared by ATC, and alert controllers to any discrepancy.

Pilot and Vehicle Operator Procedures

Pilots:

• Stop at illuminated HCLs, regardless of ATC clearance.
• Do not cross extinguished HCLs without ATC clearance.
• Report any anomalies to ATC.

Vehicle Operators:

• Adhere to HCL indications and ATC instructions.
• Operate transponders with altitude reporting enabled for accurate tracking.

Reporting:
Unexpected HCL operation should be immediately reported to ATC for investigation.

Visual Cues at the Hold Line

• Illuminated: A row of flush, red in-pavement lights signals “stop.”
• Extinguished: No red lights; proceed only after receiving ATC clearance.

Example:
If HCLs are illuminated after a “line up and wait” clearance, the pilot must stop and notify ATC.

Use Cases and Scenarios

• Peak Departure: HCLs prevent crossing during takeoff rolls, extinguishing as the aircraft passes.
• Landing Roll: HCLs illuminate for arriving aircraft, extinguishing as each intersection is passed.
• Low Visibility Vehicle Crossing: Vehicles stop at illuminated HCLs until the system and ATC clear them.

System Limitations

• Not at all airports: HCLs are prioritized at large, complex, or high-risk airports.
• System failures: Revert to basic ATC, signage, and markings if HCLs malfunction.
• Not a clearance substitute: Extinguished HCLs alone do not permit crossing; ATC clearance is always required.

Interaction with Other Lighting and Markings

Summary

Hold Crossing Lights (HCLs) are a critical, automated, in-pavement airfield lighting system designed to prevent runway incursions. By providing a highly visible, real-time stop warning at taxiway/runway intersections, HCLs supplement ATC, reduce risk, and enhance safety for pilots, ground vehicles, and air traffic controllers alike. Their integration with advanced surveillance systems and their automation make them an essential feature at the world’s busiest and most complex airports.

For airports seeking to improve operational safety and reduce runway incursion risk, implementing HCLs and the broader RWSL suite offers a proven, globally recognized solution.