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Your GPS Devices May Stop Working On April 6 If You Don't Or Can't Update Firmware (theregister.co.uk)
Zorro shares a report from The Register: Older satnavs and such devices won't be able to use America's Global Positioning System properly after April 6 unless they've been suitably updated or designed to handle a looming epoch rollover. GPS signals from satellites include a timestamp, needed in part to calculate one's location, that stores the week number using ten binary bits. That means the week number can have 210 or 1,024 integer values, counting from zero to 1,023 in this case. Every 1,024 weeks, or roughly every 20 years, the counter rolls over from 1,023 to zero. The first Saturday in April will mark the end of the 1,024th week, after which the counter will spill over from 1,023 to zero. The last time the week number overflowed like this was in 1999, nearly two decades on from the first epoch in January 1980. You can see where this is going. If devices in use today are not designed or patched to handle this latest rollover, they will revert to an earlier year after that 1,024th week in April, causing attempts to calculate position to potentially fail. System and navigation data could even be corrupted, we're warned. U.S. Homeland Security explained the issue in a write-up this week. GPS.gov also notes that the new CNAV and MNAV message formats will use a 13-bit week number, so this issue shouldn't happen again anytime soon. The site recommend users consult the manufacturer of their equipment to make sure they have the proper updates in place.
Right, thanks a lot for this piece of information, which probably solves an issue that has been puzzling to me for years.
In my free time, I fly gliders. These things are very simple craft, but usually still have some sort of on-board computer which is used for basic navigation tasks (such as "given our glide capabilities, can we still reach airfield X from where we are right now?"). And as part of that, these on-board computers of course have to use GPS. As they are permanently installed in the cockpit, these devices tend to be quite rugged, and usually are kept around for many, many years: replacements are costly, and changing something in the panel of an aircraft, no matter how small, is a major PITA (what with the necessary regulatory paperwork, and all that). So a lot of gliders fly around with positively antique - but functional - electronics on their dashboards.
In my particular glider, which is not exactly a new plane, this function is provided by a slightly ancient device from the early 90ies: a Filser DX50, which has been in the plane since it was built. And few years ago, this thing developed the classical sort of "GPS dementia" which is typical for devices that can't handle a roll-over. For my purposes (purely recreational flying), this is not a big issue: I don't care that the thing thinks it's 1995 all over again, as long as the position is correct. Which it, interestingly, still is.
The only thing about the failure which was (and still is) a bit of a head-scratcher was that it occurred far away from any actual GPS decade roll-over: as far as I remember, it croaked during the change-over from 2014 to 2015. But your explanation might be the answer: when they created the device, they probably assumed "no one will use this device beyond 20 or 22 years after manufacture", and only patched the loop-around for that long.
That's what the developers in 1978 also assumed. There is an old saying in engineering: Nothing stays around as long as an interim solution.