The US Federal Aviation Administration (FAA) has issued a warning notice to pilots that they may experience GPS outages this month. Skirting around the details of exactly why the GPS signals will be down during a series of pre-determined days and times across the month of June, the release only provides navigational coordinates from where the interference will be greatest, which also happens to coincide with the location of the US Navy's largest base located in the Mojave Desert. Neither the FAA or the US Navy have provided any further details to the press, despite requests.
The FAA flight advisory
[pdf] states that pilots should be aware that GPS systems may become unreliable on six occasions over the month including June 7, 9, 21, 23, 28 and 30th. On each of these days, testing that will interfere with aeronautical GPS systems will take place between 9:30am and 3:30pm Pacific time. Thus far, there have not been any other government advisories indicating that any other type of ground based GPS systems could be disrupted.
Aerial view of Naval Air Weapons Station China Lake
While testing will be centered on the Navy's Air Weapons Center located at China Lake, California, the effects will radiate hundreds miles out in all directions from the testing site, according to a map provided by the FAA. Aircraft will be affected once they reach an altitude as low as 50ft, while it will continue to as high as 40,000 feet above sea level.
FAA map showing range of GPS interference
As to what specifically the Navy is testing can only be speculated on. One plausible theory suggests that the Navy could be testing of military weapons systems under GPS jamming conditions, in order to simulate combat environments where jamming technology could be deployed in the field by the enemy in order to defeat them.