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20 Mar 2019 / Singapore

Global Positioning System End-Of-Week Rollover Event 2019

The Maritime and Port Authority of Singapore (MPA) would like to bring to reiterate the possible effects of the 06 April 2019 Global Positioning System (GPS) Week Number (WN) Rollover on Coordinated Universal Time (UTC) derived from GPS devices.

The legacy GPS navigation message has a ten (10) bit parameter that represents the WN. The WN parameter in the GPS navigation message “rolls over” to zero every 1024 weeks, starting from 0000Z on 06 January1980. The next WN rollover will occur 06 April 2019.

The GPS is a global navigation satellite system owned and operated by the United States government and through their Department of Homeland Security has issued a circular highlighting this issue.

The IS-GPS-200H interface specification identifies both the 10 bit WN parameter and the WN rollover events. While a GPS device that conforms to the latest IS-GPS-200 and provides UTC should not be adversely affected, not all manufacturer implementations correctly handle the 06 April 2019 WN rollover. Additionally, some manufacturer implementations interpret the WN parameter relative to a date other than 05 January 1980. These devices may experience a similar rollover event at a future date.

If a GPS device is not programmed to deal with the WN rollover, for example, the receiver may show an inaccurate date, and cause issues to its linked systems and related networks due to an inaccurate time data.

The shipping community is strongly advised to:
a. Check with your GPS manufacturer whether the supplied GPS equipment, system or networks will encounter this problem and if yes any firmware update to resolve the problem. Users shall ensure all firmware updates are completed before the rollover date.
b. Carry out a Risk Assessment on your dependencies on GPS for obtaining UTC, and what effect this could have on your operations, positioning, navigation, time keeping and potential issues if failure occurs. You are advised to have a contingency plan in place to address these failures.
c. Use the positions obtained from GPS with caution during the "rollover" date. Monitor and verify the operation of your GPS equipment and contact your manufacturer if errors are detected. If necessary, use independent means to fix the positions of their vessels, especially when navigating in busy waterways such as the Straits of Malacca and Singapore Strait as well as within Singapore's port waters.

For harbour craft masters, owners and operators are to note that:
a. MPA has verified with the manufacturers/suppliers that the AIS-B and Electronic Chart System (ECS) funded by MPA have updated the firmwares and is not affected by this rollover event.
b. However, as a precautionary measure, please monitor closely the craft position and timekeeping, and navigate with caution during this rollover event.

(For information about operations in Singapore contact GAC Singapore at [email protected])

Source: Maritime and Port Authority of Singapore Port Marine Circular No.04 of 2019

If quoting any content from Hot Port News, please cite GAC Hot Port News as the source.

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