Runway Incursion — Unauthorized presence of an aircraft, vehicle, or person on an active runway.

Runway Incursion is any occurrence at an aerodrome involving the incorrect presence of an aircraft, vehicle, or person on the protected area of a surface designated for landing and takeoff. Runway incursions are a critical safety concern and a leading risk factor for ground collisions.

Categories range from A (most severe, near-collision) to D (least severe, no immediate safety consequences). Prevention measures include improved signage, lighting, cockpit moving maps, RWSL (Runway Status Lights), and enhanced ATC procedures.