NavList:

Correct, CN isn't a backup to the situations you have mentioned, which only further confirms the initial question and response.  {Q: Is CN a backup to GPS Navigation? A: No! }

I recognize the heresy of this statement in a group which has the goal of preserving traditional means of position finding (CN).   Nothing stops us from preserving CN, but nothing is going to roll back the clock either.  Unless there is widespread spoofing, jamming or systemic GPS satellite failure, CN isn't going to be utilized for general purpose position finding.  

The development of the Russian and European equivalents to GPS push CN further to the back.  Frank makes an excellent point, simply switch to an alternate system in the event that the US GPS system is degraded.  

You make a strong argument for why SA should remain off Gary.  The risk to civil aviation and the public is quite large.  I defer to your expertise here.  Aren't there other methods to guide aircraft to runway approach in low visibility conditions?

In poking around in other message boards last night, it became apparent that the US military actively jams GPS in theater operations, mentioning Iraq specifically.  The details are obviously classified and were not discussed, yet the presence of jammers was firmly indicated.  Further, that the jammers were not supposed to affect the military receivers.  This, of course, completely obviates the need for SA.  Why bother spoofing the planet when denial of service in theater can be reasonably obtained? 

Brad