GPS week number rollover
GPS week counter overflow resets every 19.6 years.
The GPS week number rollover is a phenomenon that occurs every 1,024 weeks (approximately 19.6 years) due to an integer overflow in the ten-bit week number counter used in the legacy NAV message format. When the counter reaches 1,023, it rolls over to zero, potentially causing software not designed for the event to malfunction or display incorrect dates. This affects not only positioning but also time synchronization critical for payment operations, broadcasters, and mobile operators.
Quick Facts
- Date
- Every 1,024 weeks (NAV), starting 1999 August 21; Every 8,192 weeks (CNAV), starting 2137 January 5
Facts from the source article.
2019 occurrence
The second GPS week number rollover happened on the night of April 6–7, 2019, when the counter for week 2,047 (shown as 1,023) ticked over to zero. The U.S. Department of Homeland Security, the International Civil Aviation Organization, and other groups put out warnings about it. Among the products that had trouble was Honeywell’s flight management and navigation software, which caused a KLM flight to be delayed and many flights in China to be canceled because technicians hadn’t applied a patch. The New York City Wireless Network (NYCWiN), used by city services, went down. Other affected devices included cellphones sold in 2013 or earlier, some older Vaisala radiosonde ground stations (which stopped launches at certain sites for up to two weeks), NOAA’s weather buoys, many scientific instruments, and consumer GPS navigation units. Before the switch back to standard time from daylight saving time on November 3, 2019, Apple warned owners of iPhones and iPads sold before 2012 to update or risk losing internet access. Some Furuno GPS models had their own internal rollover on January 2, 2022, and if not updated, showed the wrong date. Honda and Acura cars from 2004 to 2012 with GPS navigation displayed 2022 as 2002, with the time off by several minutes, because of an overflow in the GPS epoch. All Porsche models with PCM2.1 were affected, per bulletin #1904 from December 20, 2019. GoPro Karma drone users reported their drones were grounded in early January 2020 due to a GPS glitch; GoPro said it was caused by the week number rollover and fixed it with a firmware update.
Other satellite navigation systems
The principle of week numbering and rollover applies to most satellite navigation systems. Galileo uses a 12-bit week numbering scheme starting on 1999-08-21 23:59:47 UTC, rolling over every 4,096 weeks, with the first rollover on February 19, 2087. BeiDou uses a 13-bit week number starting on January 1, 2006, with the first rollover on January 2, 2163. GLONASS uses a year-day format not affected by week number change. QZSS uses the same date format as GPS for its NAV and CNAV messages, with the same rollover dates. A receiver capable of receiving date from multiple systems is less likely to be confused by week number rollover.
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