Af: Henrik Mertz

GPS Rollover in December 2020


A GPS rollover will occur on December 20, 2020 for a number of products in the following series: FELCOM-15, FELCOM-16, FELCOM-70, FA-100/R and GP-310B.


A GPS rollover will occur on December 20, 2020. The following Furuno Equipment will be affected:

  • INMARSAT C: FELCOM15: Applicable to S/N Before 3533-9371
  • INMARSAT MIMI C: FELCOM16: Applicable to S/N Before 3534-2756
  • INMARSAT FLEET FELCOM70: Inmarsat F will terminate on Nov. 30, 2020.
  • AIS FA-100/R
  • GPS Sensor GP-310B (non IMO version): Applicable to S/N before 3453-5687


FELCOM15/16: New software to solve the problem is available
FELCOM70, FA-100/R, GP-310B: retrofit is recommended


Detailed information:

GPS week number rollover

The GPS system is synchronized to a different time scale than Coordinated Universal Time (UTC) and calculates time by counting the number of weeks up to 1,023rd week. After week 1,023, the week number count is reset to zero. This is called "GPS week number rollover". Subsequently, the erroneous date information on the GPS receiver clock may cause the positioning to become fixed temporarily on this date.

To resolve this, perform a cold start of the equipment via the operating menu or reboot the device.

If the GPS product is interfaced with other navigation or radio equipment requiring accurate date and time information, countermeasures will have to be taken.

Symptoms after rollover

When rollover occurs, the symptoms shown in the table below may occur.

    Models affected



S/N Before 3533-9371

S/N Before 3534-2756


 The rollover does not affect the communication function, but the   following symptoms may occur.

-The date is not automatically updated.

-The time of position dates of the interval reports in the SSAS Report and VMS Data Report functions are incorrect (5/19/2002).


Although the rollover does not affect the communication function, the service of Inmarsat F will terminate on Nov. 30, 2020.



 Although the rollover does not affect the communication function, the dates of the AIS internal system (internal GPS, display of own ship dynamic data, logs transmitting and receiving messages, alarm logs, and power ON/OFF logs) are incorrect.


Applicable to S/N   before 3453-5687


 No calculation of the position occurs.



 - Update the software for the FELCOM15/16 to software 3.11 or 5.05 depending on RF Con PCB.

 - For the models AIS FA-100, F77 FELCOM-70, Non-IMO GPS GP-310B retrofit is recommended.


How to check software version number of FELCOM15/16


We recommend arranging the software upgrade during annual surveys where necessary.


Further Reading:


Clarification of remedy to be done PRIOR to GPS roll over