Civil aviation representatives are to assess space-based navigation systems during the forthcoming 2013 peak of solar activity cycles, which reach a maximum every 11 years or so, and to examine potential future vulnerabilities.

Aviation is particularly at risk from solar flares because signals from global navigation satellite systems (GNSS) can be severely degraded by disruption to the ionosphere.

As the UK government's chief scientific adviser Sir John Beddington told an American Association for the Advancement of Science annual meeting on 19 February, the issue must be taken seriously; the Sun's current quiet period will end, and critical systems today are far more satellite-reliant - and therefore far more vulnerable - than they were during the last solar maximum in 2000.

Eurocontrol has hired an expert on the science, Emilien Robert, to gather data on the link between solar activity and the accuracy of GNSS. Robert's research for Eurocontrol involves comparing the reported position data from 400 GNSS ground stations around the world and comparing them, at times of high solar activity, with their known positions, to build a clear picture of how badly degraded the system may be by solar flares.

Solar Flare
 © Rex Features

The research is timely because Europe's satellite navigation has been enhanced by the 2 March launch of the safety-of-life capability of the European Geostationary Navigation Overlay Service, which is intended to offer precision approach options, while the Galileo GNSS remains under development.

Solar flares have already caused difficulty for air transport. US Space Weather Center director Tom Bogdan told the association meeting that an incident earlier this year saw the biggest flare in years force airlines to divert flights from polar routes in anticipation of radio disruption, while flights in the western Pacific and between Hawaii and southern California also reported communications problems.

Eurocontrol navigation consultant Roland Rawlings says a major 2003 flare knocked out the USA's wide area augmentation system for 15h. But he is confident that the forthcoming solar maximum poses no immediate danger to air navigation. Diligence is important, he stresses, but traditional ground-based navigation and communication systems have seen air transport through many solar cycles, and 2013 should be no different.

Flights that are already in the air during a solar flare are not at risk, he says, and while a severe incident could reduce the capacity of the air traffic management system, airspace authorities "could safely operate the air service".

Disruption caused by a solar flare are likely to persist only for 30min or so, he adds. The air traffic system does not face a long-term shutdown comparable, for example, with that caused by last year's volcanic cloud.

Although GNSS is becoming more significant, the potential impact on satellite navigation is still manageable, Rawlings notes. Forty percent of aircraft have satellite systems but they supplement other navigation equipment.

But it is less certain how the air traffic management system will cope with the next solar maximum, 10-11 years after this one. By then, says Rawlings, next-generation air traffic control should be heavily reliant on GNSS.

Eurocontrol's ground-station accuracy data will help it determine how much of the current ground-based navigation infrastructure it needs to maintain as back-up to support satellite-based navigation services.

Another consideration, says Rawlings, is to determine how much training controllers will need to maintain their skills on current generation systems should they need to work without GNSS. This sort of redundancy training is less of an issue in the air, as instrument-based and GPS-based data looks the same to a pilot.

Source: Flight International