Navigation and timing information from the Global Positioning System (GPS) is used by many aircraft and ground-based aviation systems.
The GPS navigation message contains date and time information in the form of a sequential week and seconds counter, which first started on 6th January 1980. As the week counter rolls over every 1024 weeks, it will do so on 6th April 2019 for the second time in history.
Systems using GPS for obtaining date and time are required to ensure that a correct progressive week count is maintained.
EASA issued a bulletin on the subject which you can find here.