Millions of GPS devices around the world could crash next month because of a Millennium Bug-style computer error, say technology experts.
It is feared that older devices using satellite mapping technology will suffer a meltdown on April 6, caused by their calendars reaching the end of their counters and literally running out of time.
It is claimed the problem could affect the navigation systems of ships and older aircraft and the digital timekeeping used by websites, electrical grids, financial markets, data centres and computer networks.
Smartphones are unlikely to be affected because they are based on more modern GPS technology.
There was a similar so-called 'GPS week rollover' on August 21, 1999 but there were barely any disruption.
Doomsday predictions about what would happen when clocks rolled over at the Millennium – the so-called Y2K bug – also failed to materialise.
However, Bill Malik, vice-president of Trend Micro, a cyber security company, has said he is not prepared to fly on April 6 because of the dangers.
He said: "The effects would be more widespread because so many more systems have integrated GPS into their operations.
"Ports load and unload containers automatically, using GPS to guide the cranes."
"Public-safety systems incorporate GPS systems, as do traffic-monitoring systems for bridges.
"Twenty years ago these links were primitive. Now they are embedded. So any impact now will be substantially greater."
The root of the problem:
GPS, the Global Positioning System, works on its own date and time scale based on counting weeks, and seconds in a week to express satellite positions.
GPS' are only able to count up to 1024 weeks before rolling over to zero again.
This is to limit the size of the numbers held in the GPS calculations.
The first ever week for GPS' started at 00:00:00 UTC (Coordinated Universal Time) on Sunday, 6th January 1980.
Since then the week number has rolled over once from 1023 to 0 at 23:59:47 UTC on Saturday, August 21 1999.
This happens every 19.7 years.
The problem is caused when GPS-based equipment or software is confused by the rollover, in an error similar to the year-2000 software problems.