The rollout of 5G connectivity to US cell phones is causing a major problem for the FAA, airlines and even engers.
In recent days, several companies have partially canceled their operations, as some planes are at risk of being interfered with by the new 5G networks. The problem is specifically focused on Band C, and how it was implemented by the FCC in the United States.
The FAA points out that 5G signals in the same band can interfere with aircraft altimeters, which use the 4200-4400 MHz band. The likely interference is also questioned by another regulatory agency independent of the FAA, Transport Canada of the country neighboring the US.
The problem is concentrated in Band C of frequencies between 3700 and 3980 MHz, auctioned for US$ 80 billion by the United States, and also present in a few countries.
The high price paid by AT&T and Verizon for a frequency band also proves that the C-Band is the most valuable part of 5G, as regulatory agencies have never made so much frequency band available for internet connections.
In the United States, the FCC was more optimistic, in addition to the N78 frequency band, which ranges from 3,3 Ghz to 3,8 Ghz, the regulatory body also authorized an expansion of Band C, going up to 3,98 Ghz.
With the maximum frequency of the connections close to 4 Ghz, the interference in the aircraft's radio altimeter system increased considerably. The FAA itself warned of the risk of this band interfering, through harmonic electromagnetic waves, in the operating range of the radio altimeters, from 4,2 Ghz to 4,4 Ghz.
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In the video above we have a classic example of interference in the radio altimeter by 5G. The equipment completely loses altitude orientation.
Anatel, for example, authorized the use of frequencies from 3,3 Ghz to 3,7 Ghz in Brazil. Without the extra band approved in the USA, Brazil does not run the same risk of interference in the aircraft's avionics systems.
Brazil is studying the use of the 3,7 to 3,8 GHz band for low-power 5G networks, preferably indoors to serve private networks and Industry 4.0. However, ANATEL may change its decision according to changes that will be necessary in the aircraft due to the United States.
By the way, how does a radio altimeter work on aircraft?
These radio altimeter frequencies are used for direct measurement of aircraft altitude in some phases of flight, but especially at low altitude. Like a sonar, the equipment is capable of measuring the time that the wave is emitted from the plane until it is reflected by the ground just below it.
In an aircraft, the radio altimeter works together with other equipment, such as TCAS, GPWS, ILS and the aircraft computer, therefore, it is a very important piece of equipment and complements the dynamic and static pressure information from the pitot tube.
With less range, 5G C Band is not a problem in airports far from cities
The United States has more than 19000 airports, it is the country in the world with the most places for aircraft takeoff and landing around the world. However, the FAA has listed only 153 airports that may be at risk of interference due to 5G C-Band networks.
These terminals, and for certain types of airplanes and helicopters, may have restrictions for operations without visibility, using instrument approach procedures.
The big reason why only 153 airports are affected by 5G, most terminals located next to large cities, is because of the low range of Band C, which is why the new internet technology needs more antennas to serve the same number of customers. In addition, the range from 3,3 Ghz to 3,98 Ghz is also less propagated indoors, which is why US operators are betting on the migration of frequencies from 600 MHz to 800 MHz to 5G technology.
In any case, AT&T and Verizon considering the impact and the hundreds of flights canceled so far, have decided to block the 3,7Ghz to 3,98Ghz band until the end of January, until the aviation industry adjusts to the new frequencies.
A study by Anatel with ANAC, for example, points out that planes can be equipped with an anti-5G filter in radio altimeters, to avoid interference in some planes where this equipment works with a frequency close to 4,2 Ghz.
