ABSTRACT
The law in respect of airspace began to be discussed towards the end of the 19th century.2 A number of approaches were possible. First, some sought to argue that air space was free and open to all. Secondly, some asserted that all superjacent airspace was subject to the exclusive sovereignty of the state by analogy with the principle in municipal law of cujus est solum, ejus est usque ad coelum et ad infernos;3 a principle which had been subject of comment in those cases concerning trespass to airspace.4 A third possible approach was to argue that in line with the law of the sea, the state was entitled to a ‘belt of airspace’ and that beyond that point airspace was like the high seas open to all. A fourth possibility was to accept the second approach, namely sovereignty of the individual state but to assert that it was subject to a right of innocent passage. These debates were being conducted in a Europe which was subject to increasing tension, particularly after 1890, between Germany and its neighbours. In these circumstances, state practice tended to be concerned with problems of national security and the fear of surprise attack. While most accepted that the airspace above the high seas was open to all, there were divisions of opinion prior to 1914; the United Kingdom tended to the view of state sovereignty over airspace but this was not a view shared by all European states. The United Kingdom legislated on the matter in the Aerial Navigation Act 19115 which enabled the Secretary of State to make delegated legislation prohibiting the navigation of aircraft within certain
areas. However, most writers accept that the rules of customary international law remained unsettled at the time of the outbreak of the European War in 1914.
