GPS Date Rollover Could Affect Older Units

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On April 6th, 2019, older GPS units may experience a range of problems because of a limitation in how they handle dates. Those problems could affect a unit’s ability to receive location data.

In older GPS units, dates are stored in such a way that they are tagged to a rollover event every 20 years or so. We are about to experience the second rollover since the GPS constellations came online. The rollover last happened in 1999, but in the last two decades the use and dependence on GPS has increased dramatically.

The Department of Homeland Security has published a bulletin on the upcoming rollover, as has the Coast Guard. Both bulletins make reference to a new GPS spec that deals with these rollovers gracefully. Unfortunately, the bulletins also warn that not all implementations of the new specification work properly. As a result, some GPS units might be prone to trouble either on the rollover date of April 6 or later.

The underlying problem stems from the way GPS units store dates. The original specification for GPS had dates stored by week in a 10-bit field, which is 1,024 weeks (or 19 years and 36 weeks). Dates for the GPS constellation started at midnight on January 5th, 1980, so the first rollover occurred on August 21, 1999. Now, 19 years and 36 weeks later, the same thing will happen again on April 6th, 2019.

Furuno has stated its units will experience the rollover on March 17, 2019, almost three weeks earlier than the published date in the notices. Furuno has a list of affected units as well as information on how to cold start the units to restore location information. It appears the date will remain wrong but the location services should function correctly. The affected units appear to all have been introduced in the early 2000s and ended sale around a decade ago.

Raymarine has posted to its forum that the company is confident most of its recent hardware will be unaffected.

Garmin has published a support article indicating it doesn’t expect trouble for its units as long as they are running current software.

Most of my research indicates the trouble is likely to be restricted to some possible restarts or even factory defaulting of equipment followed by potentially incorrect dates. I don’t believe it’s likely much equipment will end up broken, but I do suggest you check the accuracy of your GPS equipment around April 6, especially if it’s older.

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