Exceptions include military aircraft and civil aeroplanes flying no lower than 6,500 feet (2,000 m).[5] Authorisations are either given by the Ministry of Defence, for military aircraft, or by the Paris Police Prefecture and the Directorate General for Civil Aviation for civil ones. Moreover, the flying of helicopters within the limits of Paris (designated the Boulevard Périphérique) is also forbidden. Special authorisation can be granted by the Prefecture of Police for helicopters undertaking precise missions such as police air-surveillance, air ambulances but also transport of high-profile personalities.