The information in the article below may be old hat to some, but I am posting it in case it may be news or of interest to others. Not sure what "older, or poorly made" GPS receivers refers to. Article is obviously written for the non-aviation public, but has some interesting information.
CAVU, Steve (a.k.a. Downwind Jaxon) ======== Outdoor Geeks May Vanish Soon by James Glave WIRED News Service 3:00 a.m. 5.Aug.99.PDT -- Scores of backpackers, boaters, and private pilots will wander off course this month and get lost. That's hardly surprising: The summer adventure season is in high swing. But on 21 August, the US Coast Guard will be listening for maydays a little more intently. "We are going to be at a high state of readiness, just as we will be for Y2K," said US Coast Guard commander Dave Roundy. "We are going to treat this as a good practice for [Y2K]." That's because on that day, many receiver units that lock into the US military's 24 Global Positioning System (GPS) satellites will crash, although not in a literal sense. Some receivers will merely burp. Others will either shut down or display incorrect latitude and longitude figures to users. Fearing the potentially dire consequences, the Coast Guard says it has done all it can to make sure boaters check their gear for the problem. "It is hard to believe that there is anyone left out there who has not heard that they need to check their GPS receivers for the rollover, but we are going to give one last push," Roundy said. GPS provides exact navigational data to receivers that can lock in on at least four of the 24 satellites designed to calculate position. The system now guides and tracks just about everything that moves -- including rental cars, city buses, commercial container ships, overnight packages, and trucks. Recreational boaters, hikers, and private pilots have also come to rely on GPS. The system is convenient and accurate, and in many cases has come to replace older, weather-vulnerable, ground-based beacon navigation systems, such as Loran. At midnight on 21 August, GPS satellites will follow their pre-programmed instructions and send out a regular navigational broadcast to tens of thousands of receivers. The message calculates the time and resets the satellites every 1,024 weeks, or about every 20 years. As of 22 August, that count should reach 1,024 weeks. But the birds can only count to 1,023. And so they will reset their counters to zero. The event -- known less sexily than Y2K as the GPS Week Number Rollover -- is expected to cause trouble in older, or poorly made, GPS receivers. The units may have trouble locating the satellites, or stop working altogether. Worse, they may appear to be working, but display inaccurate positions, times, or dates. There are no reliable estimates on how many faulty receivers are currently in use. More than 60 companies now market hundreds of GPS receivers in the United States. Roundy said that about 20 to 30 percent of receivers won't cope with the rollover problem. For months, the Federal Aviation Administration and the US Coast Guard have been alerting boaters and pilots of the rollover issue. Not everyone will be reached in time, but just how much of a problem that will be remains to be seen. "We have been thinking that boaters and hikers are going to be the most difficult to reach," said Dave Smallen, a spokesman on the rollover issue for the US Department of Transportation. That's because backpackers don't regularly check in with public facilities such as airports, where the agencies have circulated information on the problem. Private pilots have come to rely on GPS, although labels on the units warn that they are not to be used as the sole means of navigation. The system is a godsend in Alaska, where there are dwindling numbers of old VOR radio navigation units. "Speaking for myself and many other pilots, I have quickly developed a strong dependency relationship; [GPS units] are fabulous devices," said David Carlstrom, a spokesman for Fairbanks International Airport. The Federal Aviation Administration certifies all in-cockpit navigational systems for "safety," but that rating does not demand GPS rollover compliance. Carlstrom said he has heard very little discussion of the rollover issue in the 49th state. "I haven't heard cries of alarm," he said. -0-
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