Marine Advisory: 25/2024 - Japan Radio Company, Ltd. – GPS Week Number Rollover for equipment

21 August 2024

Marine Advisory: 25/2024

SUBJECT: Japan Radio Company, Ltd. – GPS Week Number Rollover for equipment

Dear Shipowners/Operators/Masters:

The purpose of this Marine Advisory is to provide guidance on the “GPS Week Number Rollover” for Japan Radio Company, Ltd. equipment. Certain models of JRC Inmarsat, GPS, and AIS equipment are designed to reset the week number counter once every 1023 weeks, which is approximately 19.6 years.

The week number counters for the equipment listed below started the week count from 23 January 2005. Therefore, on 8 September 2024 at 00:00 AM (UTC) the week number counters rollover will occur. The specific equipment involved includes:

• Inmarsat Fleet Broadband FB500 (JUE-500)
• GPS Navigator (JLR-7500/7600)
• GPS Receiver (JLR-4331/4340)
• GPS Compass (JLR-20/30)

On 08 September 2024, the above listed models will turn the week number counter clock back 19.6 years to 23 January

2005. After the turn back of the week number counter clock, the equipment will work incorrectly under normal use.

A similar situation will occur for the equipment listed below which began the week count from December 18, 2025. Regrettably, on 03 August 2025 at 00:00 AM (UTC) the week number counters rollover will occur. The specific equipment involved includes:

• AIS (JHS-182/183）
• GPS Navigator（JLR-7800/7900）
• GPS Receiver（JLR-4341）
• GPS Compass（JLR-21/31）

On 03 August 2025, the models listed above will turn the week number counter clock back 19.6 years to 18 December 2005. After the turn back of the week number counter clock, the equipment will work incorrectly under normal use.

As a result of the week number counter clock turning back, the following abnormalities may occur in all of the previously listed equipment:

• Some date information will be displayed erroneous
• Communication function for the Inmarsat equipment will not work properly.

However, rollover of the week number counter will have no influence on GPS positioning operation.

In order to return the Inmarsat equipment and the AIS to normal operation, generally a software upgrade will be required. The GPS equipment can be returned to normal operation by adjusting the initial settings.

The following JRC Notice provides guidance on returning both the Inmarsat equipment, the AIS, and the GPS equipment to normal operations.

Notice : GPS Week Number Rollover for equipment｜JRC 日本無線株式会社

Please refer to the above JRC Notice and/or your local JRC office for additional information.

If you have additional questions or concerns, please contact the Regulations and Standards Department at RegsAndStandards@liscr.com.

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