ORIGINAL ARTICLE

April 4, 2024

Runway Status Lights (RWSL System)

As developed and deployed at major airports in the USA, a RWSL system is a fully automatic, advisory safety system which provides direct alerts to both vehicles and pilots independently of the normal traffic control system operated by ATC. Its objective is to reduce both the number and severity of runway incursions and thereby prevent runway collisions.

RELs warn that it is unsafe to enter/cross a runway.

THLs warn that it is unsafe to take off from a runway.

Runway Entrance Lights (RELs)

Illuminated RELs as seen from above.

RELs are installed at taxiway/runway intersections to provide an indication when it is unsafe to enter the runway. They are installed parallel to the taxiway centreline (which may or may nor be lit) at a distance of 2 feet from it and to one side. The first light in the pattern is installed 2 feet prior to the runway holding point marking. They continue to a penultimate light pair at 2 feet before the runway edge marking with the last light then sited 2 feet before the runway centreline lights.

Take Off Hold Lights (THLs)

THLs from above.

THLs are used at the runway departure area and provide an indication to pilots and vehicle drivers that the runway is unsafe for takeoff. They consist of red unidirectional lights installed in two longitudinal rows of 16 lights each aligned with and offset either side of the runway centreline lighting.

How RWSL Works

The system determines the locations of aircraft and vehicles on the airfield, as well as of departing and arriving aircraft using data from three surveillance sources:

• Surface primary radar returns from the Airport Surface Detection Equipment (ASDE)
• Multi-lateration calculated from the differences of time of arrival of transponder signals from aircraft and vehicles; data from several multi-lateration receiver locations are used
• Airport Surveillance Radars for aircraft operating in the vicinitiy of the airport

Integrating the data from these diverse sources has been achieved so as to support a high level of reliability and accuracy. Redundancy features allow the system to generate aircraft or vehicle tracks from single or multiple surveillance sources in case of malfunction or nonexistence of sensors or equipment. This covers the presence of many airside vehicles without transponders which respond to multi-lateration interrogation.

The integrated surveillance data is used to determine the operational status of a track including whether an aircraft object is stationary, taxiing, landing, or taking off and predicts its likely future behaviour. On the basis of this, and in accordance with pre programmed thresholds, the system determines which lights should be turned on and when and triggers activation and updates a visual display in the TWR. TWR supervisors are able to modify some RWSL settings such as light intensity and runway configuration.

Written By: Huahai