A Runway Crossing Incursion is considered here to occur when an aircraft or vehicle which requires to cross one or more active runways, in order to complete an intended aerodrome ground movement, comes into actual or potential conflict with an aircraft using the same runway for landing or take off. A crossing aircraft may be one which has just landed or is en route to an intended take off on another runway. In this context, a rotary wing aircraft which is hover-taxiing in ground effect should be considered as equivalent to a fixed wing aircraft or vehicle on the ground rather than as an aircraft ‘in flight’.