What happens if GPS stops working?

image The more dependent we become on GPS, the greater the risk that terrorists will use it to cause disruption and damage. It also puts aviation and large parts of the economy at risk from a single point of failure.

It may not be terrorists. Those morons who point laser pens at cockpits may have a new toy. New Scientist reports that a $30 GPS jammer can kill the signal.

Even accidents and mistakes can cause severe outages. New Scientist cites several examples. For example:

IT WAS just after midday in San Diego, California, when the disruption started. In the tower at the airport, air-traffic controllers peered at their monitors only to find that their system for tracking incoming planes was malfunctioning. At the Naval Medical Center, emergency pagers used for summoning doctors stopped working. Chaos threatened in the busy harbour, too, after the traffic-management system used for guiding boats failed. On the streets, people reaching for their cellphones found they had no signal and bank customers trying to withdraw cash from local ATMs were refused. Problems persisted for another 2 hours.

It took three days to find an explanation for this mysterious event in January 2007. Two navy ships in the San Diego harbour had been conducting a training exercise. To test procedures when communications were lost, technicians jammed radio signals. Unwittingly, they also blocked radio signals from GPS satellites across a swathe of the city.

The Royal Academy of Engineering has just released a detailed report (PDF), Global Navigation Space Systems: reliance and vulnerabilities that underlines the risks. While there is a risk of gross errors, the more insidious threat is “dangerously misleading results which may not seem obviously wrong.”

A significant failure of GPS could cause lots of services to fail at the same time, including many that are thought to be completely independent of each other. The use of non-GNSS back ups is important across all critical uses of GNSS.

Is it time to consider planning a non-GPS alternative as part of an IFR flight plan. For example, could you divert to an airport with a VOR or ILS approach? Could you fly a procedure or missed approach with just a VOR and no GPS guidance? As new GPS-driven glass cockpits take over – I just flew an Avidyne R9 Cirrus to Antwerp, for example – do we need to keep our old-fashioned NDB/DME/VOR/ILS flying skills current as a backup? It’s certainly something to think about.

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