GPS System Rollover 06 April 2019

If you have a GPS purchased before the year 2000 that has not had a software update and you rely on our GPS or chart plotter for navigation, you may wish to read Australian Maritime Safety Authority new marine notice.

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.

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.

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 If your GPS receiver is outdated or has not had a software update, it may revert to reading the week zero as August 1999.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.  Vessel owners and navigators should check with your GPS manufacturer regarding the status of your receiver. If you have any doubt as to whether your receiver is compliant you should contact the manufacturer or supplier.

In any situation when you are out on the water, vessel owners, and operators should never navigate using GPS or chart plotter alone.  Remember to stick your head out of the boat and make reference the chart or plotter picture compared to surrounding land or navigation features  as well as the depth of water your are moving through.

Everybody make sure they be extra careful out on the water in the coming weeks and months as some vessel owners may not realise there is an issue with their GPS until next summer.  Look out for each other and have fun.


About the Author.  Richard Hewson is a Yachtmaster, Master Unlimited and MED2 who has raced and cruised around the world with numerous maritime accomplishments including his present roles as a marine surveyor for SALUS and project manager at INCAT in Tasmania.


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