U.S. Secretary of State Hillary Clinton acknowledged on Monday that the United States and its allies are actively considering imposing a no-fly zone over Libya as a means to prevent Muammar al-Qaddafi's government from cracking down on rebel forces as the country seemingly spirals into civil war. There have been widespread reports of Libyan Air Force jets bombing and firing on protesters; rebels reportedly shot down a plane while it was firing on an anti-Qaddafi radio station on Feb. 28. Some 200 Arab groups from throughout the Middle East signed a letter over the weekend in support of a U.N. sponsored no-fly zone. How exactly do these zones work?
It depends on the circumstances. There are two primary types of no-fly zones imposed by air forces. The first is imposed by one military over another, while the two sides are at war. In practice, this type of no-fly zone amounts to a warning from one side that it will engage the other's aircraft if they are spotted in a given territory.
The second type, more applicable to the situation in Libya, is when an outside power possessing overwhelming air superiority restricts flights over a given country in order to discourage an internal conflict or humanitarian crisis. This is a relatively recent tactic, which was used most famously in Bosnia and Iraq during the 1990s. No-fly zones are often a compromise in situations where the international community is demanding a response to ongoing violence, but full military intervention would be politically untenable.
The establishment of no-fly zones is authorized under Chapter 42 of the U.N. Charter, which states that if non-military methods are insufficient for responding to a threat to international peace, "demonstrations, blockade, and other operations by air, sea, or land forces of Members of the United Nations" may be employed.
That's pretty vague, so the actual terms and rules of engagement are set up in the resolution that authorizes any specific no-fly zone. In the case of Bosnia, "Operation Deny Flight" as it was called, was imposed by U.N. Security Council Resolution 816 in 1993, and applied to all "fixed-wing and rotary-wing aircraft in the airspace of the Republic of Bosnia and Herzegovina." The already established U.N. Protection Force was charged with monitoring the airspace as well as authorizing exceptions to the ban, such as humanitarian aid flights. Deny Flight followed an earlier, less-stringent operation -- Sky Monitor -- under which only military flights were banned and U.N. Forces only could only document violations, rather than engaging the aircraft.
The ban made sense for the Yugoslav war, as virtually all the fixed-wing military aircraft in the region were under the control of one side -- the Bosnian Serbs. The zone was tested on Feb. 28, 1994, when six Serbian fighter planes were shot down by U.S. Air Force F-16s, in what became known as the Banja Luka incident.
The effectiveness of Deny Flight, however, is debatable. NATO credits it with removing air power as a weapon for the Bosnian Serb forces and pushing the conflict toward an earlier conclusion. Critics contend that it did little to prevent the worst abuses of the conflict, including the 1995 Srebrenica massacre. The mission was later expanded into an active NATO bombing campaign.