When cellphone technology collides head-on with aircraft safety


Ever since 5G wireless technology was developed, aircraft and aviation instrument manufacturers have warned that its frequencies are dangerously close to those previously reserved for aviation technology.  With the pending opening of the frequency spectrum to allow more space for 5G cellphones and other hardware, this is becoming a very real risk.  Flight Global reports:

The Federal Aviation Administration is warning aerospace manufactures and aircraft operators that 5G cellular wireless communications could impact radio altimeters starting in December.

A Special Airworthiness Information Bulletin issued by the agency on 2 November comes as the US Federal Communications Commission (FCC) prepares to permit broadband operators to transmit within the 3700-3980 MHz frequency range.

That encroaches on the 4200-4400 MHz range used by radio altimeters.

. . .

“There have not yet been proven reports of harmful interference due to wireless broadband operations internationally, although this issue is continuing to be studied,” says the FAA’s bulletin, called “Risk of Potential Adverse Effects on Radio Altimeters”.

The agency is “conducting a risk assessment to ascertain whether further mitigation is warranted”.

The FAA’s bulletin follows warnings detailed in a 2020 report published by industry group RTCA – short for radio technical commission for aeronautics.

“The results… reveal a major risk that 5G telecommunications systems in the [3700-3980 MHz] band will cause harmful interference to radar altimeters on all types of civil aircraft,” RTCA’s report says. “This risk is widespread and has the potential for broad impacts to aviation operations in the United States.”

RTCA’s report says interference could come from “5G base stations”. It warns that finding a technical solution will take “a significant amount of time”.

There’s more at the link.

If you fly at all, this should worry you.  Every commercial airliner relies on radio altimeters and other equipment to maintain a safe separation between it and the ground.  If a 5G device is too close to those instruments – either a cellphone on board the aircraft, or a ground station on or near its flight path – it might cause electromagnetic interference, producing inaccurate and erroneous readings.  A supposedly safe ground clearance might suddenly be nothing of the sort.  It’s not just civilian aircraft, either.  Military planes are also at risk – and since they often maneuver aggressively at high speed, very close to the ground, they may be in greater danger than airliners or private aircraft.

There’s only so much radio frequency spectrum to go around.  For decades it was allocated in blocks to various users – military and civilian, aircraft and ships, long-range and short-range, etc.  However, as civilian radio usage has grown exponentially, particularly with the advent of cellphones and wireless internet, its demand for bandwidth is encroaching more and more upon previously secured, reserved space in other frequency bands.  It’s a very difficult conundrum.  Does one preserve existing user rights by restricting civilian bandwidth usage, at the cost of economic growth?  Or does one prioritize economic growth at the expense of national security and aircraft safety?

It’s going to be interesting while they sort this out.



  1. Since when does 3700 – 3950 MHz "impinge" on 4200-4400 MHz?
    Unless the 5G devices are really crappy and smearing all over the spectrum, I don't see a problem…

  2. One could, perhaps, impose actual restrictions, with real penalties, on the manufacturers who cannot properly bandwidth their devices. And mandate rigorous third party testing of each device before installation, if one wanted to be particularly nasty to them. Wouldn't even take a law, just selective enforcement of various regulations.

  3. @Igor: There's always a "spillover effect", where a given frequency "bleeds" over to adjacent bands. A lot is dependent on the quality of the instrument(s) in use, both transmitter and receiver. It's been a problem since the dawn of the radio age.

  4. I think it's ironic as heck that everyone is freaking out over 5G for their millimeter wave allocation up around 24 GHz, but nobody has service up there, and the band everyone is worried about today is nowhere near there. This isn't even half the frequency of the aircraft weather radars.

    Having some familiarity with those radar altimeters and how they work (CW radars), it doesn't sound very likely to me. OTOH, I know how the RTCA and the regulatory agencies want 99.999% certainty it won't interfere under any conditions.

    1. Thing is, I don't think anyone's worried about what goes on at 35,000 feet–where, as you say, no one gets reception anyway.

      What everyone's worried about is what happens at 10,000 feet or below, where people definitely do get reception.

  5. Eh, no. Between frequency hopping avoiding active frequencies, the gap between frequencies, the difference in power available, and GPS altitude in most commercial aircraft, I see no way this is a real problem. Maybe old instrumentation in IFR situations, but even then…

  6. Yeah, nope. Not that big of a deal. the frequency separation is large enough that you are likely to have zero effect IF the radios are in tune and set up properly.

    This is the same idiocy that was used to tell us that cell phones and computers could affect the ILS and VOR receivers in the planes (which aren't used much except for landing anymore)…..not true and shows the lack of understanding of the how radios work.

    Much HuHu about nothing, really.

  7. "(which aren't used much except for landing anymore)"

    THERE is an attitude that points to why most aircraft regulations are written in blood.

    IIRC, LANDING is the single most hazardous activity an aircraft attempts. Most everything they do close to the ground can be made more hazardous by screwing with instruments that keep them from impacting it.

    Ritchie: 1000 ft for different direction of travel, and they still manage to hit each other occasionally.

  8. I would be more worried about the C-band, 2–6 GHz of 5G. Nothing like sticking a microwave transmitter next to your skull. On the other hand a 5G Super Data Layer is 37–43 GHz for high bandwith areas could be a problem. The 5G is not just one range of frequencies but 3 different ranges of .7 GHz up to 43 GHz depending on carrier and the intended purpose of the connection.

    I will avoid 5G like the covid not-vax. I am not a medical professional but I was a RF engineer and I was trained to think for myself.

  9. It's pretty common for s-band radar on passing boats to blitz our cell phone signals. Medium-sized units within about 1/2 mile will cut all cell calls and make the VOIP, WIFI and personal cell phones on board go to 'search' mode, and this phenomenon is worse for guys with 5g phones. It's not universal- some boats do this and some don't, and in areas with more than one cell tower, at times it just makes calls pass tower to tower.
    I have noticed that personal cell phone batteries discharge must faster at the anchorages inside New York harbor. My phone will run low on power after just 8 hours of idle time, as opposed to about 18 elsewhere.

    I can't see this getting better with increasing clutter.

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