Civil aviation airspace has a structured layout. Broadly speaking, the upper zone, above approximately 6,000 metres above sea level, is reserved for traffic operating under instrument flight rules (IFR). In the lower zone, flights may also be conducted under what are known as visual flight rules (VFR), whereby the altitude and speed of the flight path are selected with the aid of a map and compared in flight with landmarks on the ground (relief, roads, settlements, etc.). In doing so, the VMC standards regarding minimum visibility and cloud separation must be strictly observed in order to comply with the principle of ‘see and be seen’ (so-called ‘Visual Meteorological Conditions’).
Below a flight altitude of 300 metres above ground level or up to 900 metres above sea level, flights must be conducted outside the clouds and ground visibility must be maintained. The minimum required horizontal visibility is 1.5 kilometres. Above this altitude, a cloud separation of 1,500 metres horizontally and 300 metres vertically must be maintained. The minimum required horizontal visibility is 5 kilometres up to an altitude of 3,000 metres above sea level and 8 kilometres above that.
Pilots must observe further regulations and restrictions when flying in so-called ‘controlled airspace’ (airport control zones, defined air routes, special restricted zones, etc.).
The minimum flight altitude above ground level is 150 metres.
However, different regulations apply in the vicinity of airports, built-up areas and specific sites.