Libyan SAMs are not really an issue. Their IADS was never completely constructed, never overhauled since Libya "opened" again and thus hopelessly obsolete (no pice of equipment there is "younger" than 30 years, except if they've got some more modern MANPADs, recently). There are currently only a few SAM-sites in Tripoli and Syrte areas that are active. The SA-5 sites in Syrte look on the ground exactly like that SA-2 site near Tobruq which can be seen on some of the photos that surfaced the last few days: rusty missiles, abandoned who-knows-how-many years ago, and goats in between...

So, that's not really that much of a problem.

But, something like NFZ over Libya makes next to no sense if not the entire country is covered, particularly its borders to (Libya-friendly) countries like Chad and Niger, but also these very long borders to Algeria, Egypt and Sudan.

The area that would have to be covered by such a NFZ would be huge, and require much more assets - and foremost bases. Sigonella, Suda Bay, Akrotiri would be a literal "drop of water on hot rock": even if Algeria and Egypt might cooperate, Sudan would definitely not work with the UN.

But...it's from Chad, Niger, Mali and Sudan that the regime in Tripoli is still hauling plenty of foreigners into the country, via its southern borders (there is at least one flight every day into every of these countries, launched from Mitiga AB, in Tripoli). Yet, it's also only from there that any coalition enforcing such a NFZ could reach crucially important places like the large Sebha AB, in SW Libya, which is another - and as of yet entirely untouched - Qaddaffi's stronghold.

Theoretically, the French could "take over" in Chad (they run the country any way), and use such places like Faya Largeau, which has a well-developed airfield. Perhaps even clean up the mess left after the Libyan defeat at (Libyan-constructed) Ouadi Doum in 1987, further north, and make use of that airfield. But that would still require Deby's agreement - and plenty of tanker assets. And, any base in northern Chad would be not only extremely isolated, but also vulnerable to long-range raids of Sudan-supported Chadian opposition, based in Darfur (read: potential for spread of the conflict in Libya).

Countries like Mali and Niger are that only by names: the government of Mali, for example, is entirely unable to exercise control over its entire territory, and thus the country became a safe heaven for this "al-Qaida of Magreb" in recent years. So, "going in" there, just in order to base a few AWACS and support assets for example, would be quite messy (as much as it would probably please Algerians). The situation in Niger might be slightly better, but only "slightly", then good airfields in the north of that country are as scarce as water...