The story so far: The rollout of the 5G C-band spectrum (3.7 GHz-3.98 GHz) in the U.S., on January 19, 2022 — after a pushback since December 2021 (the original roll-out date) — led to several major airlines, including Air India, temporarily cancelling their flights to the U.S. over fears of spectrum interference with crucial aircraft navigation systems. An aircraft type largely affected in this was the Boeing 777. The two major telecom firms concerned, Verizon and AT&T, also took cognisance of appeals by the Federal Aviation Administration (FAA) and airlines about their worries, leading U.S. President Joe Biden to put out a statement on January 18, 2022. Called the “Statement by [U.S.] President [Joe] Biden on 5G Agreement”, he “wanted to thank Verizon and AT&T for agreeing to delay 5G deployment around key airports and to continue working with the Department of Transportation on safe 5G deployment at this limited set of locations.” 

An aviation expert said the main worry is of ‘radio emissions’at the top of the C-band’s 3.98 GHz frequency ‘bleeding over’ into the 4.2 GHz-4.4 GHz band used by civil aircraft radio altimeters. 

The FAA has said that there are differences in the way 5G technology has been deployed in other countries. These include lower power levels; frequencies that are ‘of a different proximity to frequencies that are used by aviation equipment’ and a different placement of antennas in the vicinity of airports. 

In Europe, 5G services are in the 3.4 GHz-3.8 GHz range. In Korea, they are in the 3.42 GHz-3.7 GHz range. 

In U.S. airspace, which the FAA calls ‘the most complex in the world’, the initial stages of 5G use will try and mirror the safeguards used in France. But even here, there are differences. In France, for example, the 5G power level (on average, 631 Watts) is still lower than what it would be in the U.S. (on average, 1,585 Watts). Also the planned buffer zones around airports in the U.S. will protect only the last 20 seconds of the flight. France has a permanent safeguard of protecting the last 96 seconds of a flight. It also has a condition that the antenna angle has to have a downward tilt to limit potential interference. The height of a 5G antenna and the power of the signal are the factors that determine how close it can be allowed near an airport or a flight path. 

The buffer zones around an estimated 50 U.S. airports will be designed to try and keep 5G signals and aircraft separate. 

In Japan, three frequency bands have been allocated for 5G: the 3.7 GHz band (3.6 GHz-4.1 GHz), 4.5 GHz band (4.5 GHz–4.6 GHz), and the 28 GHz band (27.0 GHz–29.5 GHz), according to a special article published in 2020 in the NTT Docomo Technical Journal. 

Another report in a leading technology news publication says the Electronic Navigation Research Institute, National Institute of Maritime, Port and Aviation Technology, Japan had conducted a study on 5G interference with radio altimeters, and submitted its findings to the International Civil Aviation Organisation (ICAO) in March 2021. The detailed experiments used altimeters manufactured by Rockwell Collins and Honeywell, which are the key suppliers to aircraft manufacturers, Airbus and Boeing. 

One of the findings was that there would need to be “at least 60 MHz” of what was called a ‘guard band’ to avoid interference with radio altimeters. It also made a finding of locating the high-power 5G base station 200 metres away from the approach path of an aircraft. The findings were made after ensuring that the antennas were pointed downwards. 

It says that the delays to the 5G rollout have helped it in ‘processing 5G transmitter location and power level information’. Further, under what is called an Alternative Method of Compliance (AMOC) process, it has collaborated with airlines ‘on how they can demonstrate altimeters are safe and reliable in certain 5G C-band environments’. 

Between January 16 and January 20, 2022, the FAA issued approvals clearing 78% of the commercial fleet of airlines to perform low-visibility landings at airports where the 5G C-band is in use. These are aircraft models with one of the 13 cleared altimeters — a range of Boeing aircraft (including the Boeing 777 and Boeing 787), most Airbus planes and some models of regional jets.