Question

In a low-visibility SMGCS operation, what is the specific function of stop bars installed on taxiways to prevent runway incursions?

Accepted Answer

In a low-visibility Surface Movement Guidance and Control System, known as SMGCS, a stop bar is a row of unidirectional red lights installed across a taxiway at the runway holding position. Its specific function is to provide a positive visual signal to flight crews and vehicle operators that they are prohibited from entering or crossing the runway. During low-visibility operations, when visual cues are limited by fog, rain, or snow, these red lights act as a definitive barrier that indicates the boundary of the runway safety area. The stop bar is electronically interlocked with the taxiway centerline lights; when the stop bar is illuminated red, the taxiway centerline lights leading into the runway are extinguished to prevent the pilot from inadvertently following a path onto the runway. Once the air traffic controller issues a clearance, the stop bar lights are extinguished and the centerline lead-on lights are illuminated to provide a visual path for the aircraft or vehicle to safely proceed onto the runway. This system ensures that no movement is made onto an active runway without explicit authorization, thereby preventing runway incursions in conditions where human sight alone is insufficient.

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In a low-visibility SMGCS operation, what is the specific function of stop bars installed on taxiways to prevent runway incursions?