A plane carrying European Union chief Ursula von der Leyen was forced to land in Bulgaria using paper maps after its GPS navigation systems were jammed.
Jamming has become an "invisible threat that risks devastating air travel" and leaves civil aircraft "one step away from disaster", said Christopher Jasper, The Telegraph's transport industry editor. But how worried should we be?
What is jamming?
Jamming disrupts GPS, the satellite navigation system that uses radio signals from satellites to calculate position. Jamming effectively overrides this by broadcasting high-intensity radio noise in the same frequency band as that used by the navigation satellites.
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So it's a bit like a "person shouting loudly in your ear" who stops you "hearing what someone is saying on the other side of the room", wrote Lucia McCallum, Senior Scientist in Geodesy at the University of Tasmania, in The Independent.
It's highly dangerous because it can increase the risk of collisions with other planes, or cause the pilot to mishandle the aircraft.
Who is doing it?
Authorities in Bulgaria said they suspect that Moscow jammed the GPS system of the jet carrying von der Leyen, but a Kremlin spokesperson told the Financial Times that this information is "incorrect".
Jamming is becoming more common, with a growing number of reports of its use in the conflict zones of the Middle East and Eastern Europe. It's "active along a 3,500-mile arc" from the Arctic Ocean to Oman, said Jasper.
A "clandestine" Russian base near the Polish border has been blamed for satnav interference in the Baltic region, said McCallum, and ships in the Red Sea "report frequent interference", probably from Houthi rebels in Yemen.
What can be done about it?
Some navigation systems can tune in to more than one set of satellites, so if one is jammed, there may be others available. Back-up navigation options can be used, which work using slightly different radio frequencies and maps.
Inertial sensing, which uses sensors such as barometers to directly detect movement and calculate position, can also help but it only "works well for short periods of time", and "quickly becomes inaccurate", said The Independent. There are new possibilities on the horizon, including sensors that use small fluctuations in Earth's magnetic field to detect position.
Meanwhile, everyday air passengers "have no need to worry" about jamming because it's "very rare – especially outside conflict zones", said McCallum. The aviation industry is "highly regulated and extremely safe", with "back-up options" when satellite navigation isn't working.
