What does the "yellow demarcation bar" marking indicate?

The yellow demarcation bar marking serves to indicate the presence of a runway with a displaced threshold that precedes the runway. Typically, this marking is located at the point where the runway begins, and it is used to highlight the division between the runway that is usable for takeoffs and landings and the area that is not available for such movements.

This is critical for pilots to understand during takeoff and landing procedures. Knowing that the threshold is displaced allows pilots to adjust their approach and landing techniques accordingly, ensuring they recognize where they can safely operate and when they need to prepare for the transition onto the usable runway.

When considering the other options, a hold line from a taxiway to a runway would typically be indicated by solid and dashed lines, not a yellow demarcation bar. The beginning of available runway for landing on the approach side is represented by runway threshold markings and not by a demarcation bar. A warning for tower-controlled airspace is not indicated by any runway markings but rather through signage and specific airspace regulations. Thus, the primary function of the yellow demarcation bar is distinctly to signal the presence of a displaced threshold.