For each aircraft that takes off or lands, a safety area is defined which neither other aircraft nor vehicles and persons may occupy. A runway incursion occurs when this safety area is violated. It does not matter whether other traffic was endangered or not.
Every runway incursion is recorded, analysed and assessed by DFS with regard to its severity. DFS uses a standardised EU-wide system that distinguishes between four severity categories. The majority of runway incursions fall into the 'no safety effect' category.