Where and when do runway incursions happen?
4.1 Runway incursions can occur at any aerodrome at any time and involve any type of aircraft, vehicle or person.
4.2 In good weather pilots or Air Traffic Service staff are often able to detect intruding traffic visually and initiate appropriate avoidance action. Catastrophic results are usually avoided, but the potential is certainly there.
4.3 In poor weather the probability of successful detection and timely avoidance is lower. The risk of catastrophic outcome is therefore higher for each event. The collisions at Tenerife Los Rodeos and Milan Linate both occurred in fog, which gave no opportunity for the pilots concerned to take avoiding action.