[tz] GPS Week Number Rollover Apr 6/7

Brian Inglis Brian.Inglis at SystematicSw.ab.ca
Wed Apr 10 13:45:57 UTC 2019

On 2019-04-03 16:56, Chris Woodbury via tz wrote:
> The airlines' software problems are most likely with Notices to Airman (NOTAMs).  These are
> public domain data and announcements of airspace restrictions, etc. which AeroData, Inc. has
> been contracted by the FAA to provide since 1990.  It looks like they do it for the EU, too.
> These announcements are part of the suite of software that AeroData provides.  Every media
> outlet is mentioning weight and balance (read fuel load and cargo balancing for aircraft before
> take off) and completely missing the part that does airspace restriction, route and waypoint 
> calculations that will certainly involve GPS information.  Ya' gotta love the media...

Looks like impacts appears to have been limited to unupgraded TomTom, Garmin,
and Boeing devices, including at least 16 KLM and Chinese airlines' 777 and 787
Dreamliners with Honeywell flight management and navigation software:




Comments suggest future problems will be pushed back due to 13 bit extended week
counts of 8192 week cycles in new 13 bit CNAV and MNAV messages, rolling over
about 2137 Jan 05 Sat 23:59+0000, by which time GPS will be replaced.
Older devices may not be updatable to take advantage of this, and may require
checking if they are still around at 2038 Nov 20 Sat 23:59+0000.
The precise second of future GPS times will depend on the number of leap seconds
counted by GPS but added to and skipped in UTC.

That assumes those devices did not use 32 bit time_t, common in embedded
libraries and systems to save space and speed calculations, which rolls over,
before the next GPS 1K week roll over if signed, at 2038 Jan 19 Tue
03:14:08+0000; or before the GPS 8K extended week number rollover, if unsigned,
at 2106 Feb 07 Sun 06:28:16+0000.

Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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