Will August 21 herald January 1 rollover blues?

Next Saturday night, the global navigational system known as GPS (Global Positioning System) will undergo a date-related rollover not unlike the year-2000 phenomenon with computers.

While the year-2000 problem has garnered the most publicity (older computer systems that record year dates in two-digit sequences may misrepresent 2000 as 1900), there are others quietly lurking in the background, among them the end-of-week rollover for GPS, which is nearing the end of a 20-year cycle for which it was programmed.

GPS serves as a tool for navigational assistance on airplanes and ships, although handheld devices or GPS receivers installed in card in coordination with mapping systems are also available.

The original devices linked up with a single satellite that gave the user their exact coordinates on the earth, while the newer models of the devices connect with 12 different satellites, giving the user even more precise coordinates. This also bypasses problems, such as trees and buildings interfering with the link between the device and the satellite.

On the night of August 21, at exactly midnight, the GPS will experience what is called end of week (EOW) rollover. GPS systems keep time in 1,024 week cycles (roughly 20 years), and the current cycle, which began on January 6, 1980 will end on the 21st, starting a new 20-year cycle.

But the rollover is unlikely to affect most people, according to experts here in the UK.

The UK Civil Aviation Authority (CAA) started issuing warnings and notices last October, and then again in March, warning pilots to update their systems, according to CAA Spokesman Chris Mason. "GPS is not a sole system of navigation, it is an aid," he added, noting that commercial airlines are not allowed to depend on it, and private pilots have been warned.

"GPS is rarely used in commercial aviation," according to William Gaillard, a spokesman for IATA (International Air Transport Association) in Geneva. "It is not something that has been a priority," he added, noting that satellite navigation is mainly depended upon only in the South Pacific.

One general consensus in the industry is that the media itself is creating the fears.

"I don't think it's going to be anywhere near as big as the media makes it out to be," said Graham Collins, owner of Effective Solutions, a GPS supplier in Hampshire, UK. "We sell Garmin GPS systems, and they've assured us that there should be no problem."

Collins also pointed out that his company hasn't been selling the equipment long enough to have distributed the older models, which may have problems. "The models from three to five years ago may experience a partial failure and have to be re-initialised, meaning they'll lose lock on the satellites and have to reacquire the signals," he said.

According to Peter Gibb, the UK sales manager for Garmin, this will not be a complicated process. "The older models will have to be re-initialized to obtain the new almanac," he said. "Customers can either do a cold re-start at that time, or we have software on our website that they can download into their machine." He compared the re-start process to the customers turning on their systems for the first time. "It could take 15 to 20 minutes for the system to locate the satellite," he said.

BAA PLC, which operates most of the U.K.'s major airports, including Heathrow, Gatwick and Stansted in the capital, also felt that the EOW was "not a BAA issue," according to a spokesman.

The Royal Air Force also was completely aware of the situation. "We don't believe that there will be any problems," said Tom Rounds, a spokesman for the Ministry of Defense.

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