Definition
An automated, advisory airport lighting system that uses red in-pavement lights to alert pilots and surface vehicle operators when it is unsafe to enter, cross, take off from, or land on a runway. RWSL operates independently of air traffic control instructions and is driven by surveillance of aircraft and vehicle positions. The system includes Runway Entrance Lights (RELs) at taxiway/runway intersections, Takeoff Hold Lights (THLs) on the runway centerline near the departure end, Runway Intersection Lights (RILs) where two runways cross, and Final Approach Runway Occupancy Signal (FAROS) where installed. Illuminated red lights mean stop or do not proceed; pilots must never cross or pass over illuminated red lights, and must not begin takeoff when THLs are lit.
Plain English
A set of red lights built into the runway and taxiway surface that turn on automatically when it is not safe to enter or use the runway. If you see them lit, stop and confirm with the controller before moving.
Context Anchor
Pilots encounter RWSL at equipped airports while taxiing near runways, lining up for takeoff, or approaching a runway to land.
Why Pilots Care
Provides an immediate visual backup to radio instructions that helps prevent runway incursions, a leading cause of ground accidents.
Analogy
Think of it like a red warning light at a crossing: red means stop. But unlike a traffic signal, no light does not mean you are cleared to go; you still need the proper clearance or instruction.
Intuition Check
Do not assume Runway Status Lights replace air traffic control. Red means stop or remain clear; lights off does not mean cleared to enter, cross, take off, or land.
Example Sentence 1
As we approached the hold short line, the Runway Entrance Lights illuminated red, so we stopped and queried the tower before crossing.
Example Sentence 2
After the preceding aircraft cleared the runway the RWSL extinguished, allowing the next departure to begin its takeoff roll.