Australian Maritime Safety Authority – Marine notice 1/2019

The GPS system transmits time to GPS receivers using a format of time and weeks from a start date of 06 January 1980. GPS Rollover week occurs when the data field in the navigational message sent by GPS satellites reaches the maximum limit of 1023 weeks and ‘rolls over’ to week zero. This last occurred in August 1999.

This marine notice advises Global Positioning System (GPS) users of potential issues that may occur with older GPS receiver time and positional accuracy as a result of the scheduled GPS week counter roll over on 06 April 2019.

Some older GPS receivers are unable to make the transition from week 1023 back to week zero. If your GPS receiver is outdated or has not had a software update, it may revert to reading the week zero as August 1999. When this happens, the internal clocks of these GPS receivers will experience a lack of absolute reference and may give incorrect time or position information, or may lock up permanently. Some GPS receivers may experience issues and disruptions prior to or after the rollover date. 

Some GPS receivers are repairable with upgrades, but others may become unusable. Newer receivers that are fully compliant with GPS ICD-200 should not encounter any issues. 

This marine notice is also available to download in PDF format: Global Positioning System Rollover week—06 April 2019—Marine notice 1/2019 (PDF 250 KB).

Thanks to Brian Carrick for bringing this to our attention.

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