What is approach-light control?
How the tower switches the approach lights on and off and sets their brightness, through the control system and the regulator, with the green threshold lights kept in step.
Approach-light control is how the lights are switched on and off and set to a brightness step. The tower selects it; the airfield lighting control and monitoring system carries the command to the substation.
At the substation, the constant current regulator sets the current in the approach series circuit, so all fixtures on it change together. Status returns along the same path, so the operator can see the circuit state and any fault. A local mode at the substation lets maintenance take control, which stops remote commands during work.
The green threshold lights at the start of the runway are coordinated with the approach lights, normally at a matching step set in the design, so the pilot sees one balanced picture: approach pattern leading to the threshold bar. Threshold lights may sit on their own circuit and regulator, so the control system commands both together.
Frequently Asked Questions
Q1What is approach-light control?
The means by which the approach lights are switched on and off and set to the required brightness. Commands normally come from the control tower and are carried out at the airfield lighting substation.
Q2Who controls the approach lights?
Usually air traffic control, through the airfield lighting control and monitoring system. A local control position at the substation lets maintenance staff take over when needed.
Q3How does a command reach the lights?
The control system signals the constant current regulator serving the approach circuit. The regulator then drives the series circuit at the current for the chosen step, and every fixture on that circuit responds together.
Q4Why is there a local and a remote mode?
Remote mode gives the tower control in normal operation. Local mode lets technicians run, test and isolate a circuit safely during maintenance, without commands arriving from elsewhere.
Q5How do threshold lights fit in?
The threshold lights are the green row marking the start of the runway. The control system coordinates them with the approach lights, normally at a matching brightness step set in the design, so the approach pattern and threshold look balanced and neither dazzles nor fades out.
Q6What does monitoring add?
Status is sent back to the control position, such as circuit on or off, selected step, and faults like open circuit or earth fault, so the operator knows the lights are doing what was commanded.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.