On August 22, a Y2K-style programming glitch will send some of those receivers reeling 20 years into the past, potentially causing malfunctions that could create a dangerous situation for air- and ground-based navigation systems that rely on GPS.
The system is widely used on boats, planes, trucks, and cars for tracking and navigation. Even consumers on foot can use portable GPS receivers to lead them along hiking trails.
GPS, a military system offered for civilian use, first started keeping time on January 5, 1980. But memory was only allocated to keep track of 1,023 weeks, about 19 and a half years.
So on week number 1,024 -- the week of August 22 -- GPS receivers will "roll over" to week number one.
"That 19 year cycle was so far off in the distance that all the manufacturers just really didn't think that those products would be in existence 19 years later," said Jim White, a spokesman for Magellan Corporation, a maker of GPS receivers.
The problem has been known for years, and virtually all commercial users have either taken precautions or upgraded to newer and unaffected equipment, White said. In 1993, a software fix was installed in all new receivers.
Receivers without the fix will think and act like they're operating in 1980, causing potentially serious consequences. Receivers might have trouble locating the satellites that feed the necessary data, or might not find them at all. Alternatively, the data that's returned could be inaccurate, leading GPS-users off course.
Government officials aren't sure how many at-risk receivers are currently in use. The brunt of the problem will likely be on recreational users.
Only about 7,000 of Magellan's 2 million GPS receivers will be affected, but Magellan is not taking any chances. A special Web page on the problem is now available, and users of old equipment are being offered a discount on newer versions.
The Coast Guard is recommending that all GPS users contact their receiver's manufacturer for information on the problem.
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