Universal Avionics UNS FMS Rollover Software Update

October 2022

Universal Avionics has released Mod 9 Service Bulletins to UNS-1Lw, UNS-1Fw, UNS-1Espw, and UNS-1Ew FMS (Flight Management Systems). SB (Service Bulletin) Mod 9 is a minor software change to the GPS/SBAS (Global Positioning System/Satellite-Based Augmentation Systems) module that is intended to adjust the start date of the 1024-week cycle the internal GPS uses for date calculation.

The GPS week number rollover is a phenomenon that happens every 1024 weeks, or about 19.6 years.  After the 1023^rd-week rolls back to zero, software that is not coded to anticipate the rollover may stop working or could display a date 20 to 40 years old.  

With the current software, the correct date will be calculated up to 31 May 2025.  After that date, the GPS may stop working.  With the new Mod 9 software bulletin, the correct date will be calculated up to 8 Dec 2040.

Installation of Mod 9 is highly recommended. If your Universal FMS needs repairs we recommend that you have this SB installed at that time.  Universal Avionics will not cover the cost of labor or the removal and replacement of units but will pay to have the unit returned if it is still under warranty.