How is a closed runway indicated?

A closed runway is indicated by using white or yellow Xs on the runway surface. This visual cue is intended to alert pilots that the runway is not available for landing or takeoff. The markings are typically painted at both ends of the runway to ensure visibility from the air. The use of contrasting colors, such as white or yellow, provides a clear and effective warning that the runway is closed, ensuring safety by preventing aircraft from making an unsafe approach or landing.

Other potential indicators, such as barricades or cones, can be used on airfields but are more commonly for temporary obstructions or to direct traffic rather than officially signaling that a runway is closed. Red flashing lights serve similar purposes in different contexts, often indicating a hazard or an area requiring caution, but they do not specifically represent runway closure.