How is a runway incursion best defined?

A runway incursion is best defined as a situation where an aircraft, vehicle, or person enters a runway without clearance. This definition emphasizes the safety threat posed when unauthorized or unapproved entities occupy the runway space, which can lead to collisions or accidents during takeoff and landing phases.

Understanding this definition is crucial for maintaining safe airport operations, as runway incursions can compromise the safety of both air and ground traffic. It highlights the importance of strict adherence to operational protocols and clear communication among all parties involved in airport operations.

The other definitions provided do not capture the essence of what constitutes a runway incursion. For instance, a situation where an aircraft is cleared for takeoff does not indicate any unauthorized action, and therefore does not relate to incursions. A condition where visibility is below minimums pertains to operational limitations and does not directly involve unauthorized access to the runway. Lastly, while unauthorized access to the airport premises may be considered a security issue, it does not specifically address the critical safety concern of runway incursions that occur on the runway itself.