What are runway entrance lights (REL)?
Red lights set along a taxiway that come on by themselves when the runway ahead is not safe to enter or cross. They tell the pilot to hold, even when the taxiway looks clear and a clearance has been given.
A taxiway that leads onto a runway is where a pilot is most likely to hear one clearance and see a different situation. Runway entrance lights put the answer in the pavement: if the lights ahead are red, the runway is not safe to enter.
1A red line on the taxiway, ahead of the runway
The lights are in-pavement fixtures set along the taxiway centreline, in a line from the holding position towards the runway edge. They sit on the taxiway, not on the runway, so the pilot sees them while still short of the runway.
2Lit by what is actually happening on the runway
They are driven by surface surveillance, not by a controller's switch. When the logic sees an aircraft rolling for take-off or about to land, it lights the entrance lights on the taxiways that lead into that runway. When the runway is clear they go out and the taxiway looks as it normally does.
3What the pilot does
Red means stop, or do not enter or cross, even with a clearance, and then tell air traffic control. The lights do not clear the aircraft to go; they only warn that the runway is not safe, so a clear taxiway is never taken as permission on its own.
4What sits behind the lights
The chain is surveillance, then logic, then light control, then the lights. The fixtures are red LED in-pavement lights on circuits that the system switches, so the selective-switching ideas from the taxiway entries apply, with control coming from the RWSL system rather than the tower panel.
| Light | Position | Switched by | Red means |
|---|---|---|---|
| Runway entrance lights (REL) | Along the taxiway centreline, holding position to runway edge | Surveillance logic | The runway is not safe to enter or cross |
| Stop bar | Across the taxiway at the holding position | Controller, as part of the clearance | Hold here until cleared |
| Take-off hold lights (THL) | On the runway at the departure position | Surveillance logic | It is not safe to take off |
Frequently Asked Questions
Q1What are runway entrance lights?
Runway entrance lights, or RELs, are red in-pavement lights on a taxiway that lead to a runway. They light automatically when the runway ahead is not safe to enter or cross, for example because an aircraft is landing or taking off. They are one part of the runway status lights system.
Q2Where are runway entrance lights installed?
They are set along the taxiway centreline, in a line that runs from the holding position towards the runway edge. They are placed on taxiways that lead onto a runway, not on the runway itself, and the exact layout follows the approved design for each aerodrome.
Q3When do runway entrance lights come on?
When the surveillance and logic behind the system decide that entering or crossing the runway would be unsafe, such as an aircraft rolling for take-off or about to land. When the runway is clear they stay off and the taxiway lighting is unchanged.
Q4What should a pilot do when the entrance lights are red?
Stop, or do not enter or cross the runway, even if a clearance has been given, and tell air traffic control. The red lights show a conflict the system has detected, and the pilot does not resolve it by continuing.
Q5How are runway entrance lights different from a stop bar?
A stop bar is switched by the controller as part of a clearance and lies across the taxiway at the holding position. Runway entrance lights are switched by the surveillance-driven logic and run along the taxiway towards the runway. Both show red to say do not proceed, and an aerodrome can have both.
Q6Do runway entrance lights replace the controller?
No. They do not give clearances or instructions. They are a safety net that warns the pilot when the traffic the system sees makes the runway unsafe, while the controller still separates traffic and issues clearances.
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