GPS Time Glitch Possible April 6, 2019

We Urge Boaters To Ensure GPS Units Work Properly Following Week Number Rollover

Dependence upon a 10 bit timing function called the Week Number (WN) may cause some GPS units to malfunction on and after April 6, 2019, according to a memo from the US Department of Homeland Security (DHS). You can read the official memo from DHS by clicking the link below. The text following the link is a brief, simplified, summary of the situation.

GPS III satellite
The Latest GPS III satellite, the first of which was launched in 2018 SpaceEx/

Read the Official Memo

GPS provides navigation data for safer and more convenient boating. As any navigator knows, time is one of the three key variables in solving navigation equations. Speed and distance are the other two. These so-called, “speed-time-distance,” equations are the basis of all accurate navigation. The GPS can compute these at a much faster rate than can even the most adept human. If the data is good. Garbage in, garbage out, as the geeks say.


The US Air Force sets GPS time, synching it with Coordinate Universal Time (UTC). It is in the way UTC is processed that GPS units may be affected. As an example, an error of one nanosecond, can equate to one foot of positon error. A nanosecond (ns) is a unit of time equal to one billionth of a second.

Starting in January 1980, GPS was given a 10 bit clock to process UTC that needs to be reset every 1024 weeks. This 1024 week period is known as a GPS EPOCH. When the 1024 weeks pass, and an EPOCH ends, the GPS Week Number resets to zero. This is known as a, ” rollover.”

The First GPS Epoch ended August 21, 1999. We are currently in the Second GPS Epoch and will be in the Third GPS Epoch as of April 6, 2019.


Most GPS units will handle the rollover OK Other units may not deal with it, and end up providing error messages or inaccurate data. If date-time information displays incorrect after April 6 2019, it may be necessary to either replace the system’s GPS sensor, add an external GPS sensor to the system, or replace the GPS sensing device (should no software/firmware update be available to address the 2019 GPS Week Rollover event).

Contact your GPS Manufacturer or visit its website, to see if your model is affected and what steps to take, if any.

Our main concern is that mariners are aware of the potential for error


GPS.GOV Provides A Wealth of GPS Information