Mobile telephony: 5G could jeopardize aircraft safety

The take-off of 5G in the United States will wait a little longer. The deployment of new frequency bands of the American mobile network, initially scheduled for December 5, 2021, was postponed for the first time to Wednesday January 5, then to January 19, as the new mobile telephone technology could potentially disrupt the on-board instruments.

For several months, the players in the sector have been asking the authorities and telecom operators for guarantees on the subject. But AT&T and Verizon, which bought their new frequencies from the US state in February 2021 for around $ 80 billion (around 70 billion euros), claim to have done what is necessary on their side. Caught between two fires, the Biden administration opted, Tuesday, January 4, for a further postponement of two weeks, hoping that it will finally allow the deployment of 5G smoothly.

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The Federal Aviation Administration (FAA, the US aviation regulator) alert for several years on the possible side effects of the deployment of 5G on aviation safety. The problem does not come from the technology itself, but from the fact that certain frequencies allocated to new mobile networks are close to those used in aeronautics.

“There must be vigilance on this subject”

More precisely, radio altimeters, which measure the distance between an airplane and the ground or the water surface, particularly crucial in the landing phase in poor visibility, use the frequency band which goes from 4.2 to 4.4 gigahertz (GHz). However, AT&T and Verizon are preparing to use a very similar band in the United States for the benefit of their 5G networks (between 3.7 and 3.98 GHz).

This cohabitation between services using close frequencies is common. “Each telecommunications system uses its own frequencies, explains Guillaume Ferré, lecturer at the National Polytechnic Institute of Bordeaux. In principle, they are designed to avoid problems on the neighboring spectrum. There must be vigilance on this subject, but 5G does not pose a new problem. ”

In each country, the regulator distributes frequencies to the various services that call on them, taking care to avoid any conflict. Except that many radio altimeters used in aviation are old and were not designed to block signals from the bands directly below.

“Protection zones”

“Radio altimeters pick up frequencies that they shouldn’t pick up. What we want to avoid is that a passenger switch on 5G on the plane as it approaches the airport and that this prevents the altimeters from working correctly ”, analysis Gilles Brégant, Director General of the National Frequency Agency (ANFR), the referent authority in France. Such interference could, for example, force flights to divert to seek more favorable conditions, disrupting air traffic.

Under the leadership of the US government, operators have also agreed to reduce the power of their networks around airports until July 5, 2022, time for the FAA to study the problem in detail. The question of possible conflicts between 5G and radio altimeters has also arisen elsewhere in the world. However, it is less sensitive in France than in the United States, because 5G uses frequencies more distant from those of aviation (from 3.4 to 3.8 GhZ).

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Despite this additional margin, “Protection zones have been set up around seventeen major French airports in order to limit the transmission power of 5G antennas in the immediate vicinity of these”, indicates the General Directorate of Civil Aviation at World. In parallel, “Tests are underway to remove doubts about the different types of altimeters”, adds Gilles Brégant, of the ANFR, which will make it possible to consider lifting the precautionary measures in the long term.

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Mobile telephony: 5G could jeopardize aircraft safety

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