I got this explanation from Garrecht Avioncs the manufacture of Volkslogger..

The GPS date problem shows up since end of October. Currently only from SouthAfrica and Namibia, where folks are flying now.

Not so many complaints currently, but enough to know that it will become more ...


This seems to be a new variant of the GPS week-rollover problem nobody has expected.

The cause is the Firmware on the internal Garmin GPS OEM receiver board. This board is installed in all Volksloggers, but I guess also into many other IGC logger brands (at least one of them we know has the same problem).

A quick analysis of the IGC flight recorder approval documents shows that the same GPS boards are built into
- all Volksloggers
- all Cambridge 302
- all Cambridge 10-20-25 models from 1997 onwards
older Cambridge models have still older 1-channel receivers, don't know the status of these

The firmware is, against all statements from Garmin some 15 years ago (when the issue was first discussed in the GPS community), not able to handle the week rollover properly, although there are solutions to this (most other GPS manufacturers know how to do it properly).

From all we could find out, Garmin have introduced a temporary solution at in the middle of 2000, causing all GPS OEM modules not to have a problem from 1996 to End of October 2014. Exactly, they function correctly from 1.January 2005 +- 512 weeks.


Outside this date range, all GPS25 OEM receiver boards with an init time of 1.1.2005 will have the same problem, as soon as they loose their internal time/date due to battery drain after some days/weeks (depending on the battery health).

Starting up without knowledge of last received date, they think they are 1024 weeks ago = currently, this is April 1995.

We had the problem 5 years ago with few receivers, namely the ones with an internal Init-Date of 1.1.2000. We've updated them to a newer (official) firmware, which seemed to have solved the problem, but see above.



We're working on two fixes.

1st solution
Is an (inofficial) firmware update, which (the installer software) as a "product" must not leave our house due to very possible license trouble with the Garmin company (they most probably don't like the idea that someone makes their products live longer than planned). Garmin does not support the GPS25 receiver boards in any way anymore, all software / documentation links on the Garmin website are dead.

Therefore, all affected units (or at least the GPS board) must be shipped to us, where we will fix the GPS receivers with our own firmware modification for a nominal fee covering the costs. Due to the amount of loggers sold, and expected return volumes, the processing time might become very long ...

Currently, we are calculating the costs and planning a solution for coping with the high volumes.


2nd solution
To be be negotiated with IGC within the next weeks, and can most probably postpone the problem to 2018 (first date of any Volkslogger sold + 1024 weeks), but requires a lot of programming work on very old software for many companies.

This would require a software update of all tools used for readout of the Volkslogger (Strepla, SeeYou, Garrecht DATA-GCS and VALI-GCS.exe files, IGC DLL file from Garrecht, all open-source tools, all PDA software, etc.). This software would recalculate all wrong IGC file content and names into the right, and making them.

Alternately, allowing all tools to show the wrong date at first place (on download from VL), we'd only publish a FIXGPS-GCS.EXE and a new VALI-GCS.EXE and DLL.



3rd solution (not very comfortable to the user, but least cost):
All Volksloggers with healthy GPS battery, still knowing the right date (as can be seen in the NMEA stream) should stay connected to a power source until used, and again after usage, to avoid a GPS battery outage after some days / weeks.


I hope this helps.