GPS "technical difficulties" in South East US

FAA has put an advisory warning pilots that GPS will be unreliable or unavailable from January 20th through February 22nd, 2011 due to Department of Defense tests. 

The CSFTL tag means Commander Strike Force Training Atlantic which is the Navy. 

FAA Advisory CSFTL11-01

During testing DoD could be turning civilian usage OFF on some GPS satellites which will reduce the accuracy of the GPS in concentric circles shrinking with a decrease in altitude as shown above, and explained in the NOTAM.

   

It is unclear on what will happen on the ground but the test will turn GPS OFF for periods of 15mn each hour and some observers on the ground claim their GPS was flashing different values yesterday.

So just in case take a paper map with you, and it is NOT an iPhone new bug.

FAA Advisory URL