jared@netspace.net.au
Date: Sun, 16 Jun 2019 19:06:52 -0600
This event seems to be a software bug in a system processing GPS data. A
bulletin from one manufacturer discussing one model of a commercial aviation
GPS receiver,
(https://www.duncanaviation.aero/files/intellegence/GPS_CustomerComm_FINAL.pdf
Our team has been actively working to determine a root cause. We found that
a software design error resulted in the system misinterpreting GPS time
updates due to a leap-second event, which typically occurs once every 2.5
years within the U.S. Government GPS satellite almanac update. Our
GPS-4000S-100 version software's timing calculations have reacted to this
leap second by not tracking satellites upon power-up and subsequently
failing. The U.S. Government distributed a regularly scheduled almanac
update with this leap second on 0:00GMT, Sunday, June 9, 2019, and the
failures began to occur soon after. The next scheduled update by the
U.S. Government to the GPS constellation is set for next Sunday, June 16 at
00:00Z. At this time, we do not believe this update will have the time
information that triggers this error. We are testing additional impact of
this next almanac update. ...>>
Handling leap seconds is a software risk which has affected many systems
beyond GPS receivers (a few of which have appeared in comp.risks). GPS
receivers have had other time concerns, perhaps most recently the 6 April
2019 week number rollover if a receiver used the legacy 10bit value and
firmware updates were not available or applied.
What the almanac update issue was nor why it would be experienced using the one update is not clear. There has not been a leap second for more than two years and none is currently planned (IERS Bulletin C ...announcements of the leap seconds… https://datacenter.iers.org/data/latestVersion/16_BULLETIN_C16.txt
Testing of this receiver's software is extended by the 'power-up’ pre-condition mentioned in the bulletin; an aircraft manufacturer's notice illustrates the complexity of this unit's initiation https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf%3Fas_id%3D50304