The US Air Force (USAF) issued a notice stating that recently a number of GPS users have reported outages.
Investigation reveals that all GPS satellites are operating properly, but that certain GPS receivers are erroneously ignoring the satellite health status information being broadcast.
Satellite Vehicle Number (SVN) 64 broadcasts a data message indicating that SVN 64 is unusable for navigation. Certain receivers are using the information regardless, resulting in outages or corrupted, incorrect position calculations.
Users experiencing GPS outages should contact their equipment manufacturers for software/firmware updates. (5/15/14).