What does a white runway letter "X" indicate?

A white runway letter "X" indicates that the runway is permanently closed. This marking is a standard visual signal used to communicate to pilots that they should not attempt to land on or take off from that runway. The presence of the "X" is important for safety reasons, as it prevents confusion and helps ensure that pilots are aware of operational statuses of the runways they may be looking to utilize.

In aviation, runway markings are crucial for guiding pilots during landing and takeoff procedures. The white "X" serves as an obvious deterrent and reinforces the communication that the runway is no longer in service for any type of operation, thereby safeguarding aircraft and personnel from potential mishaps associated with taxiing or landing on an unusable surface.