5G vs. Aviation
Like any new technology, 5G cellular has its fair share of PR challenges. Is it safe, do we need it, will it work? We have looked at some of the safety issues in previous articles, so this time we turn to look at the allegation that 5G is unsafe around airports. What is the truth behind this—and might there be an issue that is way larger that 5G or aviation?
What is the Problem?

Some of the new frequencies allocated for 5G cellular use are in part of the radio spectrum known as C-Band (3.7 to 4.2GHz). Originally, this band was mainly used for communication using large satellite dishes. These days, most of that use has migrated to higher frequencies, where smaller dishes can be used. This has freed up some spectrum that is ideally suited for the needs of 5G cellular. It is actually between the two Wi-Fi bands (2.4GHz and 5GHz), and that makes it an excellent next step for cellular. The bad news is aircraft radio altimeters operate in the 4.2 to 4.4GHz band — just 200MHz higher than the top of 5G.
On the face of it, that should not be a problem. It is easy to design front-end filters so that the radio altimeters do not “hear” the lower frequency 5G signals. Regardless, the 5G systems are legally operating within the terms of their license—so the problem is one for the altimeters to solve.
These altimeters are not the normal instruments used in flight, which use barometric pressure to determine altitude over a wide range. These instruments are only used close to the ground when very accurate measurements are needed during low visibility instrument landings.
What is the Solution?
The initial solution enacted by the FAA in the US was to impose a 2 mile exclusion zone around airports where C-Band 5G would not be allowed. Earlier this year that was rescinded, but certain aircraft using altimeters found to be affected by “Adjacent Channel Interference” from 5G were no longer allowed to land in poor visibility at certain airports. This has caused a big problem in the US because affected aircraft tend mainly to be short-haul ones operated by the low cost regional airlines. Canada has not yet authorized frequencies above 3.7GHz. We also have regulations requiring that cell sites close to airports tilt antennae downwards to reduce problems.
The Real Issue
If all radio altimeters had been built properly (not “on the cheap”) then they would reject radio signals outside their band of interest—something fairly easy to do, but something that costs money. This problem is not restricted to 5G or radio altimeters for that matter. For example, if you receive TV using an antenna rather than cable, you may find that radar or even 4G cellular “interferes” with reception at times. Your Wi-Fi connection might be restricted when a local microwave oven is in use. Both might be blamed on the source but are actually poor design of the receiver. You may need to add a special filter to block local cell sites that use a frequency close to your TV channel. It is not the fault of the cell site (although they are certainly the cause)—rather it is the fault of the TV tuner accepting frequencies outside its design range. You may need to reposition Wi- Fi Access Points away from other strong RF sources.
What Should I Do?
Be aware of the issue of what is known as “Adjacent Channel Interference.” You may not have to fix every vulnerable piece, but your help desk needs to know what to do regardless.
If you’d like to comment on this article or explore these ideas further, contact me at peter.
This article was published in the
April 2022
edition of The TMC Advisor
- ISSN 2369-663X Volume:9 Issue:1
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