Buildings, aerials, towers, cranes, cableways, high-tension pylons or even taller constructions can represent flight hazards and affect the safety of aircraft and helicopters. All such installations therefore have to be registered and must submit to an examination of their technical aeronautical impact right at the planning stage. Constructions are regarded as flight hazards if they are in built-up areas and have a height of at least 60 metres and, outside such areas, a height of at least 25 metres. Furthermore, specific regulations are in force in areas around airports. FOCA checks whether a construction should be permitted given its likely effect on the safety of air travel and determines which safety measures such as markings and/or warning beacons should be provided. FOCA registers and monitors all constructions which represent a flight hazard and publishes notices about them for pilots. As well as being marked on official national maps of Switzerland, current flight hazard data are available in electronic form at the Federal Office of Topography.