How can a pilot tell if a runway is closed?

The correct answer is that a closed runway will have an X over the landing designator. This is a standard aviation practice and is universally recognized in the flight community. The "X" marking serves as a clear and unmistakable visual indicator to pilots that the runway is not in use and should be avoided. This marking ensures safety by preventing aircraft from inadvertently attempting to land on or take off from a closed runway.

Additionally, runway closure procedures are typically established by the governing aviation authorities, and pilots are trained to look for these visual cues in their pre-flight assessments and during approach to an airport. The use of an "X" is an effective way to convey crucial information to pilots quickly and effectively, regardless of the time of day or lighting conditions.

While lights may be used at night or in low visibility conditions to indicate runway status, they can sometimes be missed or misinterpreted. The presence of other aircraft does not necessarily indicate that a runway is open or closed; airports can have simultaneous operations on multiple runways. Therefore, depending solely on the presence or absence of aircraft is not a reliable method to determine runway status. Runway closure is always indicated through established marking conventions, making the "X" over the designator the most definitive answer.