“Starting today, it appears the US military will be testing a device or devices that will potentially jam GPS signals for six hours each day. We say ‘appears’ because officially the tests were announced by the FAA but are centered near the US Navy’s largest installation in the Mojave Desert. And the Navy won’t tell us much about what’s going on.
The FAA issued an advisory warning pilots on Saturday that global positioning systems (GPS) could be unreliable during six different days this month, primarily in the Southwestern United States. “
Source: FAA Warns of GPS Outages This Month During Mysterious Tests on the West Coast
