Definition
A row of in-pavement red lights installed across a taxiway at a runway holding position that can be switched on and off by air traffic control. When illuminated, they prohibit an aircraft from crossing; when extinguished by the controller, they signal that the aircraft has been cleared to proceed across the holding position.
Plain English
Red lights set into the taxiway surface at a runway entrance that the tower can turn on or off. Red on means stop. Lights off means the controller has cleared you to cross or enter the runway.
Context Anchor
Seen during SMGCS low-visibility taxi operations, usually near runway holding points or other controlled taxiway locations.
Derivation
“Stop” means to halt, and “bar” here means a straight line or strip across a path. In this term, the “bar” is not a physical gate; it is a line of red lights across the taxi route.
Why Pilots Care
They give positive visual control to prevent runway incursions when painted markings and signs are hard to see.
Analogy
Think of it like a red traffic light stretched across your lane. When the red line is on, you stop; when it is switched off and you have clearance, you may continue.
Intuition Check
“Controllable” does not mean the pilot controls the lights. It means the lights can be controlled by the tower or airport lighting system.
Example Sentence 1
During low-visibility operations, the crew held short of Runway 28L until the controllable stop bar lights extinguished and the controller issued a crossing clearance.
Example Sentence 2
We held short of the runway because the controllable stop bar lights were still illuminated.