The Division of the World’s Airspace


On land, borders are usually precisely defined. You know when you enter or leave a country, province, or state. But what are the boundaries in the air, where borders can’t exist and furthermore the lack of dimensions complicates everything? Here we’ll explain a bit how “the wild blue yonder” is divvied up; what are the main laws which govern it; and which are the international bodies which regulate it. 

Horizontal Airspace  

To start with, “horizontal airspace” refers to that which is above each of the world’s countries. In addition, as with maritime jurisdiction, countries with a sea coast also have assigned to them a sovereign strip of airspace extending outward from their coasts 12 nautical miles (just over 22 kilometres).

This division was agreed upon more than a century ago, at the Paris Convention of 1919 on air navigation. It was one of a number of accords signed right after World War I to regularise international systems and agreements. Then as World War II was entering its endgame in 1944, the Chicago Convention on International Civil Aviation was signed, which established a number of worldwide standards, including:

– Rules on air navigation. Among them, it was agreed that any civilian aircraft could fly over any country, unless that country for reasons of war rules its airspace to be a zone of military exclusion. It also provided for the sovereignty of each country over its own airspace and its right to maintain its own rules, as long as they are in accordance with the spirit of the convention. 

– The creation of the (Iinternational Civil Aviation Organisation (ICAO), whose main function is bureaucratic and to support diplomatic communication, but also to innovate and research new air-transport policies. 

– Rules relating to the regulation of international air transport.

Communication between pilots and ground control, including the establishment of English as the lingua franca.

As far as assigning horizontal airspace 12 nautical miles beyond a country’s coasts, that came much later, in the 1982 United Nations Convention on the Law of the Sea, which despite its name also covered airspace.

Then there’s international airspace. While in principle all of this is held in common. But there are several exceptions, such as agreements that give some countries control over some of that space. This is the case with Portugal, which has jurisdiction over a large part of the airspace over the Atlantic Ocean, and United States over the much of the Pacific Ocean. 

Vertical Airspace 

But what about vertically – upward from the ground? This rather more complex. For starters, the upper limit is not defined in any of the international agreements. Neither in the Paris nor the Chicago Convention is there a measure on where airspace ends and outer space begins, that is, leaving the field of aviation and entering the field of astronomy. There’s a tacit agreement on the upper limit that cannot be exceeded by aircraft, about 21 kilometres (13 miles) up. 

The World Air Sports Federation sets the boundary between airspace and outer space at 100km (62 mi.), called the Karman Line. However, the United States considers that at over just 80km (50 mi.) you’re talking about astronauts and not pilots. It’s a bit odd, because no current aircraft can yet reach that height,  nor do these air borders have any legal implications.  

Vertical airspace in essence is divided into controlled airspace and uncontrolled airspace. Controlled airspace is where air traffic control services are provided. It’s subdivided into classes A, B, C, D and E, according to the control service provided, and the classification assigned by the ICAO. The zones are established for three types of traffic: areas with a lot (near airports); air traffic flying under instrument flight rules (IFR); and secured areas like an air defence zone. Uncontrolled airspace is where no air traffic control services are provided (except flight information), either because it’s not necessary or because it’s not possible to provide it. The ICAO assigns these as zones F and G. Today, zone F barely exists (it was reassigned to zones E and G).