At 6:00 pm EDT new information tables began to be uploaded to the GPS satellites. These tables, known as almanacs, contain information that allow GPS receivers to predict which satellites are in view at an estimated location and time.
These are used by the receiver to lock onto the correct satellites and to continue proper operation as satellites fall below the horizon and others rise into view. GPS receivers that are not fully compliant with the current standards may experience GPS receiver malfunctions when trying to use the new almanacs.
The GPS EOW rollover occurs every 1,024 weeks — about once every 20 years. The GPS system calculates time by counting the number of weeks since Jan. 6, 1980 — up to a maximum of 1,024 weeks. At midnight between Aug. 21-22, 1999 Universal Time Coordinated (UTC) (which is 8:00 p.m. Eastern Daylight Time) the GPS week "counter" will roll over to zero weeks.
The Department of Defense (DOD), which operates the GPS satellites, says this will not create problems for the GPS satellites or DOD's GPS ground control center, but it could present a problem for consumers who use GPS receivers and related applications. That's because after Aug. 21, 1999, receivers that are not built to standards could process satellite data incorrectly and display inaccurate information.
Consumers who depend on noncompliant GPS receivers for geographic locations at sea, on land or in the air, may experience one of the following problems with their receiver:
It will be unable to locate the satellites, resulting in the receiver not working.
It will take more time than usual to locate the satellites.
It will appear to be working but display inaccurate positions, times or dates.
"Year 2000," or Y2K, is a similar but distinctly different problem. DOD has determined that the GPS satellites and its ground control center will operate properly after Dec. 31, 1999. But if consumer GPS receivers and applications are not Y2K-ready, they could process satellite data incorrectly at that time.
If you use GPS, check with your receiver manufacturer to find out if your receiver and applications are EOW rollover- and Y2K-compliant. You may want to check the Coast Guard Navigation Center's web site, where the Department of Transportation has posted a list of receiver manufacturers and contacts.
You also can call the free Y2K consumer hotline (1-888-USA-4-Y2K) for manufacturer contact information. You will need to tell the manufacturer your receiver's model, serial number, and the firmware version or release date displayed on the startup screen.
GPS rollover and other Y2K-related information at US Air Force
