Aircraft flying under instrument flight rules must maintain prescribed minimum separation distances from each other. These are five nautical miles (about nine kilometres) horizontally and 300 metres vertically. If two aircraft do not maintain this separation, this is called an infringement of separation.
The minimum separation distances are set in such a way that there is still sufficient safety buffer in case of an infringement. An infringement of separation is therefore not equivalent to a dangerous air traffic situation.
Every infringement of separation is automatically recorded and subsequently investigated, regardless of whether it was caused by an air traffic controller or a pilot. In this way, possible weaknesses in the system can be detected and closed.
DFS uses a standardised EU-wide system that distinguishes between four severity categories in its assessments. The majority of runway incursions fall into the 'no safety effect' category. In the top category 'serious', there has not been a single case in recent years.
