Recently, the "5G interference storm" has been making a lot of noise in the United States on the other side of the ocean. As of our deadline, the tug-of-war between U.S. telecom operators and the Faa's (FAA) is still not over, and the final direction of this matter is full of unknowns, but what we can make clear is that 5G networks in specific frequency bands will cause interference to the radio altimeters on the aircraft, but not to a large extent, and the impact on the domestic aviation industry is minimal.
Because of this, this storm has a very different degree of discussion in the East and the West, but the science still has to be taken seriously, why does the FAA say that telecom operators will have an impact on aviation safety by laying 5G base stations near airports?
The causes and consequences of the 5G storm
As early as 2020, the FAA raised concerns with the federal government and the Federal Communications Commission (FCC) that the C-band 5G network to be auctioned would cause interference to the aircraft's radio altimeter, and the C-band network auctioned this time had a frequency of 3.7-3.98 GHz, which was too close to the 4.2-4.4 GHz frequency used by the airport radio altimeter, which could cause signal interference in extreme cases and affect the aircraft's near-earth landing.
▲Image source: PCMAG
Aircraft safety is no small matter, and the FAA and the Aviation Radio Technical Committee (RTCA) launched a joint review, which formed a 5G task force for a six-month review that included quantitative assessments of radio altimeter performance and the development of interference models and assumptions to predict the level of interference received under a wide range of operating conditions.
A comprehensive assessment concluded that 5G telecommunications systems in the 3.7-3.98 GHz band would cause harmful interference to radio altimeters in all types of civil aircraft, including commercial transport aircraft, business jets, general aviation aircraft, transport and general aviation helicopters.
This risk is widespread and has the potential to have wide-ranging implications for U.S. aviation operations, including the potential for catastrophic failures in the absence of appropriate mitigation measures.
Most civil aviation aircraft currently use two altimeters to determine flight altitude: barometric altimeters are used at high altitudes, and radio altimeters are used for height measurement during take-off and landing.
The latter principle is similar to radar, so it can also be called radar altimeter. The aircraft emits radio waves to the ground, which are reflected and re-received by the aircraft, measuring the altitude of the aircraft by measuring the time it takes for the waves to travel back and forth. This altimeter only operates within 750 meters of the ground, so it is generally used during the approach (the process of flying against the runway when descending) and the landing phase.
▲ Image source: Daily Mail
Therefore, the FAA is worried that the radar altimeter is interfered with by C-wave signals, resulting in the pilot not being able to read accurately, affecting altitude judgment.
In low-visibility weather, pilots can not use the naked eye to observe ground obstacles and distance from the ground, radio altimeter is equivalent to the pilot's eyes, if this "eye" can not see clearly, it will threaten the safety of the entire crew and passengers.
Because these are assumptions based on predictive models, the FCC and the two major U.S. telecom operators, AT&T and Verizon, disputed the review as having no real-world reference value.
This is like not being able to use a mobile phone on an airplane, which is a potential risk in theory, but it has not been corroborated in reality, and is more like a preventive measure.
However, the FAA has issued an airworthiness directive requiring pilots to prohibit some driving operations that require radio altimeters, including automatic landing, when there is a C-wave 5G network in the flight environment.
Why other countries have not encountered similar storms
Operators in nearly 40 countries in Europe and Asia are currently using C-band 5G networks and radio altimeters have never been reported as affected.
The European Aviation Safety Agency issued a statement on December 17, 2021, saying that the controversy over the so-called "5G band interference" is limited to the US aviation community.
At this stage, no unsafe risk of interference has been identified in Europe.
In the European Union, 5G networks operate at a lower frequency than U.S. carriers plan to use, reducing the risk of disruption to the area around the airport.
In addition to the United States, aviation regulators in France, Canada, Japan and other countries have also introduced relatively mild restrictions on 5G networks.
First, Canada and Japan have limited the frequency of 5G base stations near airports, while France's approach is more flexible.
In February 2021, the French Civil Aviation Authority warned that the use of 5G equipment on the aircraft could interfere with the electronic equipment on board, resulting in an error in altitude readings, and suggested that the 5G equipment be turned off or set to flight mode during the flight, and later the French Civil Aviation Authority stipulated the establishment of a "buffer zone" around the airport to limit 5G signals, and the antenna must be tilted downwards to prevent potential interference.
Although this will reduce the ability of 5G signal radiation, it is also a compromise after multiple measurements.
How will this storm end?
U.S. operators are fiercely resisting this, more because they spent tens of billions of yuan to shoot 5G network licenses in the 3.7-3.98GHz C-band, which means that the money is lost and is not conducive to the promotion of 5G networks in the United States.
Why are C-band 5G networks so important to AT&T and Verizon? Because they need a wider coverage of 5G network radiation technology, the higher the frequency of radio signals, the greater the energy, but also the narrower the radiation range.
The C-band network, which is at the center of the public opinion storm this time, belongs to the mid-band (Mid-Band, usually referring to the 1GHz-6GHz band as the intermediate frequency). The speed of this band is a large distance from the theoretical peak speed of 5G, and it can even be said to be only a little faster than the 4G network, but it has both coverage and bandwidth capabilities, which is more practical for the United States, which has a large land area and sparse population.
Why don't we see T-Mobile, one of the three major operators, in the reports on this controversy? Because they don't currently have a deployment for C-band networks.
They chose the 3.45-3.55GHz band to cover the midrange band, which has a large safety buffer from the radio altimeter's operating frequency, so T-Mobile was able to stand alone in the storm.
The mainstream 5G network bands in mainland China are n41, n78, and n79, all of which are medium frequency bands, but they do not intersect with the operating frequency of the altimeter and are not affected.
Of course, this does not mean that we can use the mobile phone on the plane without any worries, whether it is 5G or 4G, when flying, we also need to comply with the provisions of the civil aviation code, turn off the mobile phone or turn on the flight mode when taking off and landing.
Whether this dispute can be ended as soon as possible depends on whether the two sides are willing to take a step back.
For operators, they can do something similar to France's: create a 2-kilometer buffer zone around the airport and approaching airspace to minimize interference from 5G signals to aircraft.
For the FAA, they are calling on operators to postpone 5G rollover plans, while checking aircraft equipped with C-wave interference, more advanced altimeters, and resuming flight plans for this part of the flight.
As of Jan. 20, the FAA has allowed 90 percent of the U.S. commercial fleet to make low-visibility landings at airports with C-band deployments, including Boeing 737, 747, 787, Airbus 319, 320, 330, 380, and other aircraft.