back to article Aircraft can't land safely due to interference with upcoming 5G C-band broadband service

The new 5G C-band wireless broadband service expected to rollout on 5 January 2022 in the US will disrupt local radio signals and make it difficult for airplanes to land safely in harsh weather conditions, according to the Federal Aviation Administration. Pilots rely on radio altimeter readings to figure out when and where an …

  1. Gordon 10


    There's gotta be more to this story. Unless these are legacy radar altimeters that are already on their way out and in fast declining use, it appears impossible and murderous to allow them to co-exist with this 5G service.

    The FAA has a history of rolling over on safety decisions (737MAX) - is this another one?

    1. Anonymous Coward
      Anonymous Coward

      Re: WTAF?

      These particular radar altimeters are only used on a small number of small aircraft - it's not on A380s. Precision approaches are localiser/ Augmented GPS

      It's only some altimiter models that use this band and only a few (one?) telcos that are rolling out 5G in this band - although presumably will get worse as more telcos need to use more spectrum.

      I suspect it's more a good "5G" + "Plane Crash" headline

    2. Anonymous Coward

      Re: WTAF?

      The absolutes in the story would be less absolute if the FCC's opinion was balanced with the FAA's opinion.

      While both the new 5G and the existing radio altimeters use the C band, the FCC has assigned them separate (but adjacent) sub-band spectra. Theoretically there should be no problem but the FAA is worried about interference (just as they were with cell phone use on planes well before 5G).

      Currently, I understand that the carriers are discussing limiting the maximum power of the 5G nodes and I assume tests are planned in the real world to see if the possible interference happens.

      1. Nonymous Crowd Nerd

        Re: WTAF?

        "I assume tests are planned in the real world"

        Surely! Surely tests have already been carried out!

        1. TeeCee Gold badge

          Re: WTAF?

          No, but Boeing are planning extensive live testing, as usual.

          1. iron Silver badge

            Re: WTAF?

            I know you're joking but actually Boeing has already said the FAA are talking bull. The airplane manufacturers and FCC say there will be no issue with 5G interference so it seems the FAA are flexing their muscles because they can.

            1. wub

              Re: WTAF?

              "actually Boeing has already said the FAA are talking bull."

              I'm with the earlier post casting aspersions on Boeing, after that little 737Max design change. Of course they think everything's absolutely fine. I sometimes wonder whether Boeing execs check to see what hardware is listed for flights they are planning.

              Anyone know what Airbus said about this issue?

    3. bombastic bob Silver badge

      Re: WTAF?

      Are you sure it was the FAA and _NOT_ the FCC behind this?

      Regardless, crashing airplanes hurts EVERYBODY (not just those on the plane)

    4. FuzzyTheBear

      Re: WTAF? Turn the tables.

      I see that allowing 5g to come to existence when the airplanes been using the band for a long time is simply irresponsible. Another example of profit over safety. Shut the 5g and the problem goes away. It's just freaking phones and gadgets , not human lives.

      1. Paul Hovnanian Silver badge

        Re: WTAF? Turn the tables.

        The voices of millions of autistic gamers sitting in their parents' basements cried out in terror and suddenly were silenced.

        1. Claverhouse Silver badge

          Re: WTAF? Turn the tables.


      2. John Brown (no body) Silver badge

        Re: WTAF? Turn the tables.

        "It's just freaking phones and gadgets , not human lives."

        Seriously?? WTAF!!! People NEED their 4K pussy videos. Nothing must be allowed to stop that.

        1. Claverhouse Silver badge

          Re: WTAF? Turn the tables.

          I too like cats.

      3. ThatOne Silver badge

        Re: WTAF? Turn the tables.

        > It's just freaking phones and gadgets , not human lives.

        It's just big profits for you, against insurance claims somebody else will have to settle. So it's a no-brainer really.

        Besides your private jet doesn't use that specific frequency, so why worry? Everybody who is important to you is safe and will get wealthier...

    5. JoeCool Bronze badge

      Re: WTAF?

      The canadian government has already announced 5G restrictions around airports. Seems they've already come to a conclusion about how 5G can "coexist". So yeah, I'm suspicous too.

      1. Paul Hovnanian Silver badge

        Re: WTAF?

        "around airports"

        Until a medivac helicopter can't reach an accident scene because everyone uploading pictures of the wreck is messing up its terrain avoidance system.

  2. Magani
    Thumb Up

    A better explanation?

    If you want a deeper and a bit more techy explanation, try this one from a B777 pilot.

    1. elkster88

      Re: A better explanation?


      See this diagram.

      5G vs. Radar Altimeters

  3. EricB123 Bronze badge

    Just Say it Like it Is

    “Harmful interference to the radio altimeter could cause these systems to operate in an unexpected way.”

    Translated in plain English - "crash".

    1. rnturn

      Re: Just Say it Like it Is

      My preference: "make inadvertent contact with the terrain"

  4. doug_bostrom

    Faster delivery of what by volume is mostly pointless video, or more reliable and also mostly useless travel?

    Decisions, decisions.

    1. Kane

      "Faster delivery of what by volume is mostly pointless video, or more reliable and also mostly useless travel?"

      Cats vs Holidays?

      1. CrazyOldCatMan Silver badge

        Cats vs Holidays?

        Cats every time.

        (My cats told me to say that)

  5. Fruit and Nutcase Silver badge


    Total Inability To Sense Underlying Position

    1. Anonymous Coward
      Anonymous Coward

      Re: TITSUP

      Telemetry Indicates Terrain Somewhere Under Plane (we just don't know how far under)

  6. spold Silver badge

    I'm assuming -5G is your landing acceleration

  7. Kev99 Silver badge

    Funny. I saw an article that said the European and Japanese aviation authorities found no interference. Hmm..."Curiouser and curiouser", said Alice.

    1. Anonymous Coward
      Anonymous Coward

      The term 5G refers to a very wide range of spectrums. The under claim by the FAA is only on part of that. So it is perfectly possible to use 5G without such interference.

      1. ARGO

        The article specified 3.7-3.98 GHz.

        3.7-3.8 GHz is already widely deployed outside the US (as band n78), and 3.8 - 4.0 (n77), while less common, is reasonably widespread. Planes are still flying in the countries that have these.

        So either the US has some seriously naff electronics controlling their planes, or this is an FAA / FCC turf war.

        1. rnturn

          Band, schmand

          Years ago, I was involved in a study that found that radio transmitters -- even though they weren't transmitting in a band protected for aviation use -- could interfere with ILS receivers. Multiple transmitters near an airfield will result in all sorts of harmonics hitting the front-end of the ILS receiver that can result in interference within the protected airspace. The whole study began when a airfield's ILS testing found that signals in the receiver driving the needles were being affected by a broadcast of a Cleveland Indians game. I didn't get to attend the high-level meetings between the FAA -- who was trying to protect the airspace -- vs. FCC -- who were being pressed by licensees/investors who wanted to erect radio towers wherever the hell they pleased -- but I can imagine they were somewhere between humorous and maddening.

  8. Anonymous Coward
    Anonymous Coward

    The C band is not that high frequency stuff offering 1Gb/s per channel, but actually more or less the the same frequency as 4G (starting a the frequency where 4G ends) but a much wider channel. The plan is to use that width to run more channels in parallel, and do that with towers that are 2 km apart, and a low frequency signal that passes through walls. You'll need a phone that includes enough receivers in parallel to take advantage of it - you haven't heard about that part yet. How many people are actually going to go for the more expensive phones and the increased service bill - when they can get the same performance with 1Gb (*) fiber to the home and Wifi 5Ghz? (* 2Gb fiber to the home service will be widespread by the time 5G rolls out).

    The carriers have dreams of driving fiber service and even Wifi out of existence with 5G, and base their need for C band on that premise.

    1. Stoneshop
      Big Brother

      The carriers have dreams of driving fiber service and even Wifi out of existence with 5G

      Hahaha. Why would I let data take such a roundabout way with systems just decalinguini apart? Never mind that the majority of those systems don't even know about wireless in whatever form it presents, and that I prefer to keep an eye on what data gets out.

    2. Paul Hovnanian Silver badge

      "The carriers have dreams of driving fiber service and even Wifi out of existence with 5G, and base their need for C band on that premise."

      Starlink has dreams of driving terestrial carriers out of business. Given Musk's performance vis a vis AT&T/Verizon, I'm betting on the satellites.

      1. Anonymous Coward
        Anonymous Coward

        Starlink has no such dreams, they're very clear that wired service is (or *should be*) superior. Even cellular should be able to offer better service than Starlink in high density areas. They should be able to put legacy satellite Internet providers out of business.

        (Source: 1 year with Starlink service).

      2. John Brown (no body) Silver badge

        "Starlink has dreams of driving terestrial carriers out of business."

        No. That's neither an intention nor, for the foreseeable future, possible. Starlink and/or similar simply can't offer service to a city of millions, never mind the rest of a country, all at the same time. That's need so many sats in orbit it'd be permanent night! On the other hand, it might help cool the planet. Is Musk building a world girdling rail network and a very very large train? Or is that outsourced to the Chinese silk road project?

  9. Piro Silver badge

    Frequency Unbearably Crowded, Knowingly Extremely Disabling

  10. Jim Whitaker

    What the actual.

    Would it not be good if there were regulatory bodies which could review and determine the use of spectrum and any potential interference with other users.

    1. ThatOne Silver badge

      Re: What the actual.

      Which would automatically spawn the lobbying groups making sure the findings of those regulatory bodies don't interfere with some people making as much money as they possibly can (without risking too big a prison sentence).

      Unfortunately the conflict between "What suits most" vs. "What suits some" is all too often won by the influential "some".

  11. tip pc Silver badge

    Die Hard 2

    Have these people not seen Die Hard 2?

    1. FrogsAndChips Silver badge

      Re: Die Hard 2

      If they're like everyone else, they've seen it and quickly forgotten it.

    2. John Brown (no body) Silver badge

      Re: Die Hard 2

      There was a sequel?

      1. ThatOne Silver badge

        Re: Die Hard 2

        That's why it was called "die hard".

  12. Anonymous Coward
    Anonymous Coward

    Many things going on here

    What you are seeing play out is a reaction to a RTCA SC239 report released in 2020 in regards to this possible situation. Various spectrum and aviation regulators have been working on this issue in plane sight (pun intended) since this report. For example, the European spectrum regulators and their leading mobile group PT1 are on the case, with some real world testing in Norway and France in recent months. Japan and France have put in precautionary measures around having 5G base stations near some aerodromes. The Australian aviation regulator has issued an airworthiness bulletin to highlight this issue and reports a case of interference, but no further evidence to back up this statement. I believe the Japanese have bench tested some altimeters against idealized base stations on near by frequencies and have yet to show any issues as yet. The pace of this work, we are talking months and years, not weeks shows that there is concern but its not plane grounding 5G base station shut down concern as yet.

    1. Graham Cobb Silver badge

      Re: Many things going on here

      Never forget the one true maxim about politics: "All politics is local".

      As the AC says, this has been known about, and worked on, for some time. But in the US there seem to be several possibly important non-technical factors involved:

      1) Regulatory politics: FCC own the spectrum, FAA own the planes. Each feels they should be in control of this issue.

      2) FCC is in the pocket of the telcos. It has been for many years, but particularly under the last administration (Ajit Pai and Donald Trump). More spectrum availability keeps spectrum prices down - favouring the telcos. And, for some reason, US telcos are massively keen on 5G as a last mile replacement (presumably because their residential broadband service is so appalling compared to the rest of the world).

      3) FAA has had some bad press recently (!) and could do with an issue to divert attention. Particularly one where they can be portrayed as the "safety good guys". And they can do it without upsetting their stakeholders - Boeing.

      1. Version 1.0 Silver badge

        Re: Many things going on here

        So 5G corporate profits may cause a few crashes, I expect that the profits are seen as far more important that the risk of a crash.

        1. This post has been deleted by its author

        2. John Brown (no body) Silver badge

          Re: Many things going on here

          "I expect that the profits are seen as far more important that the risk of a crash."

          Yeah, 1929 and 2007. Oh, not that sort of crash? :-)

  13. Wim Ton

    Frequency allocation

    I did not see aircraft altitude meters as an application in the C-band:

    1. wub

      Re: Frequency allocation

      If you are not already a Wikipedia editor, you can easily become one - this is your big chance to improve a Wikipedia entry!

      1. Wim Ton
        Thumb Up

        Re: Frequency allocation


    2. Col_Panek

      Re: Frequency allocation

      They're 4.2-4.4 GHz and run an FM-CW waveform. Their receivers suck and have poor filters, but in olden times nobody had adjacent interferers.

  14. Sparkus


    no C Band 5G within 15 miles of an airport for the next 5 years?


    1. TJ1
      Black Helicopters

      Re: no C Band 5G within 15 miles of an airport f

      Apparently not that simple - helicopters frequently fly at or near the 500 foot minimum altitude and rely on ARNS altimeter to avoid CFIT (Controlled Flight Into Terrain).

  15. TJ1

    Underlying Technical Details

    It's important to understand that ARNS (Aeronautical Radio-Navigation Service) operates in the 4200 - 4400 MHz range for transmit and receive. The issue appears to be a combination of ARNS receivers being sensitive to (strong) signals outside the immediate band and the cellular base-station signal strength in 3700 - 4000 MHz.

    Historically the band has been used for low-power services that do not suffer 'bleed' so ARNS receiver design especially didn't require tight band-pass filtering.

    Frequency Allocations: [2] slide 7

    3700-4000MHz Fixed Mobile

    4000-4200MHz Fixed Satellite

    4200-4400MHz Aeronautical Radio-Navigation

    "It should be understood then that any interference that is unpredictable and that can mix with the linear FM waveform, thereby causing the radio altimeter to mistake the mixed signal as terrain has the potential to cause a radio altimeter to report a false altitude. "

    [0] page 9 "1.1 Radio altimeter modulation and receiver sensitivity"

    Affected Fleet:

    "All FAA Part 135 helicopters are now required to have an operational radio altimeter

    ◦ Approx. 22,000 operational civil rotorcraft

    ◦ Some FAA Part 91 aircraft require altimeters for certain operations such as Cat II ILS, etc.

    ◦ Approx. 34,000 general aviation/private aircraft

    ◦ All large passenger aircraft

    ◦ Approx. 7000 US based civil aircraft

    ◦ Plus international carrier"

    [1] slide 5 "Equipage and operation US National Example"

    [0] ITU-R M.2059-0 "Operational and technical characteristics and protection criteria of radio

    altimeters utilizing the band 4 200-4 400 MHz"!!PDF-E.pdf

    [1] "Radio Altimeter Interference"

    [2] "FAA Radar Altimeter and Compatibility with 5G presentation"

  16. Grinning Bandicoot

    Between the present 4G service and the present aeronautical band an amateur secondary band exists for satellite uplink. It is at that portion of the band that the concern exists. There are fewer satellite enthusiasts then projected towers so a possible conflict was present but unlikely. With the service full time the probability of a conflict soars. What is curious is why now? What is Wag the Dog up to?

    I had forgotten the fun of reading those publications written in response to the CFRs. By the time you reach the end you've forgotten the reason that you started

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