back to article Watchdog clears 90 per cent of US commercial aircraft to land in low visibility at nation's 5G C-band airports

Nine out of ten of America's commercial aircraft can land in low visibility using radio altimeters at US airports that have nearby 5G C-band masts, the country's aviation watchdog said this week. There is some concern that signals at the top of the 5G C-band, namely 3.98GHz, could bleed into the 4.2-4.4GHz band used by …

  1. Gene Cash Silver badge


    So the airline industry is figuring out that the cell industry isn't going to roll over and buy them new altimeters.

    1. David 132 Silver badge

      Re: Finally.

      Honestly, I'm just very puzzled that the airline industry and the FAA waited until the 11th hour to wake up and go "huh, wait, maybe we ought to check this stuff for interference risk". It's not like the C-band auction, frequencies, or deployment schedule were a closely-guarded secret.

      1. The Axe

        Re: Finally.

        "Honestly, I'm just very puzzled that the airline industry and the FAA waited until the 11th hour"

        You're assuming that because the FAA is some government organisation it is super efficient. In reality most government organisations are run by incompetents and staffed by those with minimal ability to do their job.

        1. Andy The Hat Silver badge

          Re: Finally.

          The FAA were probably far too busy trying to administrate obscure ways to delay the environmental reports for SpaceX Boca Chica expansion.

        2. Anonymous Coward
          Anonymous Coward

          Re: Finally.

          The FAA is actually one of the better and more responsive Federal agencies with a healthy and fact-based agency culture. There's more nuance to this situation than a casual article would imply.

          This First Officer provides a good overview:

      2. imanidiot Silver badge

        Re: Finally.

        That is because BY LAW, the onus is on the phone companies to ensure there is no interference. The reason there is "no problem" (not entirely true) in Europe and Japan is that they are using slightly lower frequencies (so more margin) and lower max power levels per mast.

        The FAA was assuming (bad assumption) the phone companies would figure it out and ensure there would be no interference. Now that there potentially is they have to make a stink about it. They've been doing that for a lot longer behind the scenes without making noise but phone companies have basically been sticking their fingers in their ears and shouting "we paid good money for these frequencies so we're going to use them" over and over without even trying to work with the FAA to solve the issue.

        1. Tom 38

          Re: Finally.

          The phone companies do ensure there is no interference, but the manufacturers of the radar altimeters assumed that there is nothing in the bands around the ones that they are supposed to use and allow those bands to bleed in to what the altimeters are reading.

          As you say, less of a problem in other places since they are using slightly lower frequencies so the altimeter's assumption still mostly holds, but its the altimeters that are faulty, not the 5G masts.

          1. imanidiot Silver badge

            Re: Finally.

            I think you misunderstand the problem. All radio transmitters have "harmonics" outside the main band (and outside their allocated frequency band). 5G is no different. There is a spec on how much harmonics and "spurious" RF they're allowed to generate outside the band and for the vast majority of applications this is more than enough to ensure no problems arise as the receiver of equipment designed outside the band would just reject the low "background noise". Radar altimeters however have to be (in order to function) very very sensitive and cannot easily just filter out noise from their own transmission, which makes it far easier for them to get influenced. The slightly higher margins in the EU mean that the main peaks of the harmonics lie just outside the band of radar altimeters while in the US the harmonics lie just INSIDE the band of the radar altimeters (thus causing problems) and their higher power means that they are more likely to lead to problems.

            Radar altimeter manufacturers did nothing wrong when these devices were designed. RF spectrum rules as applied back then would have ensured no harmonics and spurious emissions from devices in adjacent bands would have interfered (as the frequency bands separating them would have been wider).

            Thus the rule still stands, it's the 5G masts causing radio emissions outside their assigned spectrum band (or atleast increasing background noise levels) that can interfere with radar altimeters and it's thus 5G musts that must prevent that from happening.

            1. Yes Me Silver badge

              Re: Finally.

              If that was the case, it would be all or nothing. The FAA has just made it clear that only some altimeters installed on some aircraft have inadequate filters. It's therefore not the 5G base station that's at fault.

              1. Electronics'R'Us

                Radio / Radar Altimeter technology

                There are 2 primary methods used.

                1. Radio. Frequency Modulated Continuous Wave devices. These transmit a continuous signal where the frequency is changes at a relatively slow rate. The height is calculated by the frequency difference between the current transmit frequency and the received frequency. The actual modulation comes in a wide range of flavours.

                2. Radar. These are pulsed devices and the height is determined by the round trip time of the signal.

                Those two types have very different receiver characteristics (and the first type has many variations depending on the modulation scheme used), and the first type appears to be more susceptible to the problem.

                Therefore it is not necessarily a problem in the altimeters which worked perfectly well previously and would have been extensively tested against the requirements in place at the time they were designed as they are classed as safety critical for passenger transport aircraft.

        2. Anonymous Coward
          Anonymous Coward

          Re: Finally.

          Read this morning(*) that Europe is using 3.4-3.8 GHz rather than 3.7-3.98G, so a bigger gap to the 4.2-4.4G used by the altimeters

          (*Politifact debunking a 'if FAA is worried about planes and 5G, think what it does to your bodies' FB story)

        3. Yes Me Silver badge

          Re: Finally.

          No, the phone companies are not on the hook as long as they don't transmit power on the wrong frequencies. As long as they stay on their allocated frequency without sidebands, they're fine with the FCC.

          What's not fine is an altimeter that doesn't properly filter out neighboring frequencies. And you can tell from the FAA's list exactly which planes carry such defective altimeters. Bad new for the altimeter makers concerned - it's their product at fault.

          1. imanidiot Silver badge

            Re: Finally.

            That is NOT how US RF spectrum allocations work. 5G harmonics are causing ng problems outside of THEIR allocated band, and that is a problem for the telco's. Not for the users of (old and designed to an older spec) radar altimeters that can't handle interference (that is, again, inside the frequency spectrum allocated to them. NOT in the 5G spectrum band)

            The FCC very much cares about RF emissions outside the allocated band, especially when it interferes with neighbouring allocations. (Which is why istr the FAA had objected to that slice of spectrum getting sold in the first place but was ignored because it didn't have definitive proof)

    2. imanidiot Silver badge

      Re: Finally.

      You do realize that the way radio spectrum laws work, "new" users to a frequency band are the ones that have to make sure they don't interfere with existing users in other bands, right? And if that means that the telco's bought a useless frequency because someone in a different band has problems due to "out of band" sensitivity that is still THEIR problem, not the existing users.

      It's not even about "buy them new altimeters" because the way aviation and instrument certification works means that many older planes out there simply cannot be equipped with newer altimeters because they are simply not certified to use those new instruments. If somebody even makes one that can be installed in those older planes. (and just to make you feel old, first gen Boeing 777 came into service 1995. That is nearly 30 years ago. 747-8 is newer, first was delivered in 2012, but strongly based on earlier generations and might still be limited in what instruments it can take). So if it means "buy them new altimeters" it means pay for the cost and ongoing "responsible authority" of certifying those new instruments for use in every old plane out there.

      1. Anonymous Coward
        Anonymous Coward

        Re: Finally.

        1. Obtain a small bit of the spectrum with lots of unused area on either side.

        2. Create devices that only emit in your band, but suffer interference from anything in the unused areas either side.

        3. Sit back and relax as you have effectively reserved a massive chunk of the spectrum while only having paid for a small part of it.

        1. imanidiot Silver badge

          Re: Finally.

          Only if you can show that A: you followed best design practices at the time of designing the thing, B: altering your device is prohibitively or unreasonably expensive and that the other party refuses to pay for such an expense(and they'll bring in an outside expert to make sure the cost is actually real and not inflated) and C: that the functionality of your device cannot be easily and affordably be performed by a different device not subject to those bandwidth problem (plus nowadays you'd probably not get an FCC approval for such a device)

          With what you describe they'd probably tell the judge " we made this little antenna filter box to reject anything outside their bad, it costs 2 dollars, they should have put it in their design". All of this is a long way of saying, it all has to be within reason. Judges will know if you're taking the piss and rule accordingly.

          But if you had done that in the 50s and it became an important device for safety or every day utility then yeah, that pretty much sums it up.

        2. Snake Silver badge

          Re: Sit back and relax

          That is not true. In the United States, devices that operate in the "unregulated" 900mHz, 2.4gHz and 5gHz frequencies *must*, by law, accept interference without damage or restriction - see the actual FCC approval label on these devices to read the necessary operating conditions.

          However, "regulated" frequencies have much stricter operational requirements. And, for ultra-important frequencies such as these radio altimeters, extra special requirements are allocated due to their fundamental importance.

  2. sanmigueelbeer

    The FAA determined that anomalies due to 5G C-Band interference may affect multiple airplane systems using radio altimeter data, including the pitch control laws, including control laws that provide tail strike protection, regardless of the approach type or weather

    Is this the same FAA which "approve" the Boeing MAX before the two fatal crashes? (I'm just askin'.)

    1. nintendoeats Silver badge

      So you are complaining about the fact that they did their job, by bringing up a time when they didn't?

    2. Lars Silver badge

      "Is this the same FAA which "approve" the Boeing MAX before the two fatal crashes? (I'm just askin'.)"

      I think the problem was that the FAA naively let Boeing self approve the MAX and more.

      And indeed it's the higher max power levels used in the USA that makes this difference too.

      Juan Browne at Blancolirio is mostly very reliable in stuff like this.

      Also note the fact that it matters what came first.

      1. Yet Another Anonymous coward Silver badge

        >I think the problem was that the FAA naively let Boeing self approve the MAX and more.

        No the FAA has to let Boeing self approve the MAX - they are the only ones that know how it works.

        The FAA aren't like the teacher with the "correct" answers in the back.

        What they failed on was not pushing Boeing's risk assesments. If you have a critical component you have to consider what happens when it fails, and the various modes that it can fail in, and what sort of redundancies are needed. And all that has to be documented.

        This is what the FAA failed to do. You don't need to be an expert on the 737-MAX, or even on aviation, to know to ask these sort of questions !

        The problem is that the FAA wasn't just rubber stamping Boeing's approval it was rubber stamping Boeing's auditing of it's own approvals

      2. John Brown (no body) Silver badge

        "Also note the fact that it matters what came first."

        What's on second. Who's on first!

        1. julian.smith

          Who's on first

          Donald Trump was born on third and thinks he hit a triple.

          LMAO (not very) United States

  3. Kev99 Silver badge

    How about that. Industry doesn't get a chance to cry poverty because of government regs and jack up there prices three to four times to cover actual expense. Let the shareholders eat it for once.

  4. William Higinbotham

    In 2008, NASA helped launch the Machine-to-Machine Intelligence (M2Mi) Corp to develop IoT and M2M technology, as well as the 5G technology needed to support it.

    So why did NASA, the FCC, and FAA failed to see a problem until now?


  5. EricB123 Bronze badge

    Oh, the Paine!

    An airport in Washington State called Paine Field had to totally shut down yesterday because of thick fog and the fear the 5G could cause problems with the altimeters on various planes. So easy to see how the whole supply chain mess happened with this level of competence.

  6. julian.smith

    USA: airtravel / Boeing

    If it's Boeing ... I'm not going

    Travel to the "U"SA: why would any sane person travel to that Covid-infected, gun nut haven, Trump infected shithole?

  7. Sixtiesplastictrektableware

    (Not far from) Point Avoider

    Up in canadaland I got a little chuckle when I read that guvs making the similar US determination consist of a lawyer, an educator, a philanthropist and a HR consultant.

    Yep, sciencey minds for sciencey problems.

    Kinda un-sciencey myself, I contend that it'd be better to test fly an empty bird for possible brick-flight than to find out with bodies on board.

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