FAA To Take Regulatory Action Over 5G Altimeter Interference


The FAA plans to issue a Special Airworthiness Information Bulletin and an Airworthiness Directive in coming days concerning the rollout of 5G cellular phone service in 46 major metropolitan areas of the U.S. on Dec. 5, according to Reuters. The actions are expected to limit the use of automated systems on aircraft that rely on radar altimeters (also called radio altimeters) and it’s possible that flight delays and cancellations will result. Reuters also quoted a letter from FAA Deputy Administrator Bradley Mims that says the agency shares “the deep concern about the potential impact to aviation safety resulting from interference to radar altimeter performance from 5G network operations in the C band.”

In an auction of radio spectrum last year, the major telecoms paid a total of $78 billion in an FCC auction to get access to a thin slice of the finite range of available radio frequencies to carry 5G signals. Those signals will be in the 3.7 to 3.98 GHz part of the so-called C-Band, which is apparently the sweet spot for carrying the data-heavy 5G signals. Radar altimeters operate in the 4.2-4.4 GHz frequency range (their sweet spot) and the fear is that the nearby powerful cell signals will cause interference for the avionics. The FCC approved the use of the spectrum for 5G saying “well-designed [radio altimeter] equipment should not ordinarily receive any significant interference (let alone harmful interference).…” But aviation groups say the risk for thousands of aircraft is real and the FAA seems to agree.

The precise nature of the impending rulemaking hasn’t been revealed yet but radar altimeters are fundamental to the operation of instrument landing systems since they provide the primary altitude information for decision height in Cat 2 and 3 approaches. They’re also the source of altitude data for ground proximity warning systems. 

The U.S. approach to the 5G rollout differs from that of Canada, which is also concerned about radar altimeter interference. As we reported earlier, Canadian radio spectrum authorities have placed restrictions on the use of 5G transmitters near major airports to ensure there is no interference with radio altimeters. Major telecoms in Canada are protesting the move, saying it will keep them from offering the latest wireless services to many businesses and private customers in the heavily industrialized and populated areas around major airports.

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    • “Government” just does what their corporate masters pay them to do, in this case the telecoms. I’m in this business and 5G is first, not needed, second, potentially/probably dangerous for humans and other biological life. I really hope all the research I’ve read on this is wrong, or we’re in for a very troubling 20 years before we finally figure it out.

      • First of all, there is absolutely nothing dangerous or harmful about 5G signals.
        The frequencies used are non-ionizing. We are surrounded by electromagnetic waves in those frequencies all the time. The transmit power of your phone is so miniscule as to have no measurable effect on the body.
        The real issue with 5G is the fact that it is blocked by walls, trees, rain, fog, and possibly even holding your phone wrong!

          • i can back it up, i have spent 3 years testing and analyzing 5G systems. unless you are climbing up the pole itself and plastering your face right up against the RF Emitters. it isnt going to affect you one bit.

            RF Energy is non-ionizing radiation. that means it is NOT the cell structure destroying kind. the most you can get from Non-Ionizing radition is whats called a RF Burn. think of it like this. imagine your household microwave oven. you jam a screw driver into the safety interlock, hold your arm inside and press COOK. your arm is immediately going to feel like its getting hot, not on the outside, but from the inside. this is what a RF Burn feels like. and only the higher amounts of ERP and wattage have the potential to kill you if they radiate through your body at critical points, like your chest or your head.

            3g is harmless, 3g is harmless, 5g is once again…..harmless.

            in fact, AM KHz frequncies are the most harmful of any RF Signals. AM Emitters are the most dangerous to be within close proximity of as they cause RF Burns the easiest of all of the signal types.

            Ionizing radiation, like Gamma Rays, Alpha Rays, X-Rays, etc etc, is the kind that induces medical malformities and illnesses.

        • you are confusing 5G UWB ( Ultra WideBand ) with 5G LB/MB ( Lo and Mid Band ) LB and MB operate at the same distances as 4G LTE.

          UWB is the system that has very little range and is much more sensitive to obstacles and other issues because of how its designed.

    • “well-designed [radio altimeter] equipment should not ordinarily receive any significant interference (let alone harmful interference).…”

      Weasel words: “well-designed”, “should not”, “ordinarily”, “significant”. That’s a helluva lot of weaseling in one sentence!

  1. Sounds like the FCC caved in to the telecoms on this one. They knew beforehand that radar altimeter receivers (and GPS receivers to some extent) were close in frequency and that the radar altimeters in service weren’t designed to be selective enough to be unaffected by strong transmissions from the 5G systems. When new technology like 5G is introduced, the manufacturers must bear the burden of preventing interference with installed technology like GPS and radar altimeters which were designed, sold and installed prior to 5G. Telecom companies ought to be doing R&D for higher frequency parts of the SHF band above 10GHz. In the end it comes down to money having been spent on 5G systems and the revenue to be reaped by the telecoms. Canada’s approach makes sense since radar altimeters and GPS receivers are most likely to be affected by nearby 5G transmitters when aircraft are lower and closer during takeoff and landing at an airport. Getting the FAA and FCC to agree on something like this is the responsibility of the top levels in the administration. Write your legislators if you want something to happen but good luck fighting the telecom companies.

    • both the FCC And Canada’s Spectrum Management Authority have defined that the tolerance of 5G to nearby frequencies is within their own guidelines.

      I have tested this myself as a IT and RF Engineer.

      5G UWB operates in a completely different band ( MMW 28-35 GHz ) and is unaffected. the separation of 5G LB/MB ( which is the common 5G, not the super fast UWB version ) operates 500MHz away, low to high for each respective device sets, and the closest is 220MHz.

      Both the FCC and the Canadian Authorities authorized 5G as safe with respect to both GPS and RA’s, but now suddenly its a problem.

      interestingly enough, its ONLY the FAA and TCCA who are making these claims. and yet 5G Operates in several other countries and regions without a single problem.

  2. Maybe it is just me but when radar altimeters are certified they should operate within a certain radio frequency range. The FCC maintains gaps between usable bands to prevent interference. If the altimeters are affected by frequency’s outside of this range then the altimeters are defective and should be replaced this should be on the company that manufactured them.

    Now if the FCC has changed the buffer between usable frequencies that is a bit different. Modern electronics can be designed to operate in a much narrower band. I am guessing that most of the radar altimeters that are effected by this are older ones. so the question is how long should the FCC be required to maintain support for older equipment by maintaining large gaps between usable frequencies 20 years, 30, 40? I know we in the aviation market are not used to it but electronics are now considered obsolete after about 5 years. 10 at the most and given the disparity in market size between aviation and consumer electronics we will lose every time in this fight it is on us to adapt.

    • If all electronics had to go through the FAA certification process we would still be using X86 pcs running Windows Vista.

      I remember when all electronic devices had to be turned off for the entire flight on commercial airlines. Were the airline avionics systems hardened to allow relaxation to allow current rules?

      • no, they weren’t. they have always been hardened in some form or another for another reason. one of the hidden reasons those rules came into place was to keep PAX aware of their surroundings in the event of an emergency during TO and Landing. one additional rule is that window shades should be open, but the FAA deregulated that to airline preference.

        in fact, a mobile device will stop operating on a signal above 1200-2000 AGL depending on terrain and elevation of which tower its connected to.

        no PED like a CD player or media player with no RF Device can cause any kind of EMI/RFI that would even affect the next PAX over from you.

        and now that planes carry their own WiFi for inflight usage, how does the WiFi not affect other devices and the aircraft systems itself?

        As a IT and RF Engineer and former HEMS Pilot, i can tell you why. THEY DON’T interfere with them.

      • Most likely more knowledge, including of new systems, and perhaps hardening (note Special Conditions against EMI/RFI).

        I would not bet on cellular phone signals not being available vertically, what type of antenna is used in sparsely settled areas (a monopole radiates in all directions, normal antenna sites have antennas aimed horizontally to cover users in sectors – three or four antennas depending on service provider).

  3. What’s missing from this and every other story about 5G is whether anyone has actually tested it.
    Has anyone demonstrated harmful interference with radar altimeters? Or GPS as the concern was last year? Or is it just the “potential impact to aviation safety?”

  4. A properly functioning radar altimeter is only really critical for auto-land. And, when the weather is lower than CAT II minimums, fail-operational CAT III (Alert Height vs. Decision Altitude) the radar altimeter is critical for the last 100 feet of vertical guidance and for the landing flare, when visual cues are lacking.

    BTW, as to the illustration for this article, I’ve never seen a radar altimeter that indicates above 2,500, agl.

    • That interference concern is serious.

      I have seen high-range radio altimeters, WW II vintage.

      Pacific Western Airlines installed them in Hercs and perhaps 707s for use by navigators, knowing both physical height and pressure altitude helped guestimate movement of weather systems thus winds.

      A self-contained box, with display in front, plus antennas of course.

      I wouldn’t be surprised if military has newer ones.

  5. yeah, sorry, but as a former HEMS Pilot myself, turned IT and RF Engineer – one who has spent a good deal on the 5G project, until I see an established report proving these claims, from the TCCA, the Canadian Government Spectrum Management Authority, the FCC and the FAA.

    All I see is a bunch of organizations barking nonsense at each other to get the high ground. 5G is here to stay. Telecom Industry has spent billions on developing and implementing 5G around the world. why is it, only Canada and the US have a problem with it? nearly every country operating 5G has had ZERO problems with it concerning aviation.

    as another user pointed out there are high altitude RA Units still being used, but no where near as common as the current devices. i could see unit circuitry degradation as a factor in allowing more than nominal amounts of interference, which is normal. I hope this FAA AD is just a inspection Directive to ascertain age of a RA, and its diagnostics by a certified electronics facility to test them for airworthiness.

    Looking at the actual spectrum in place, and testing this via simulation with 5GLB/MB Encoded signals, using dB levels nearby a 5G Low and Mid-Band power output. with RA’s operating at 3700-3980 MHz and 5G Low and Mid Band towers operating at 4200-4500 MHz that’s 500Mhz of separation low to high, the closest frequency separation is just under 300 MHz at 220 Mhz. That’s PLENTY enough separation per FCC Guidelines and Canada’s guidelines.

    After testing this in a simulated run of a RA passing within 2-5000 Feet of a tower itself operating at day time power output of ERP. there was less than 2% interference between the two and zero harmonic residual saturation of the two signals. That’s WELL Within the FCC and Canadian Guidelines for acceptable tolerance of EMI/RFI. I took a older RA Design and tested it to the same situation, again, 6.34% Signal Interference, again, not as well within, but still within FCC and Canadian Guidelines for device certification. That being said, the Canadian Guidelines mandate a device inspection for anything above 6% that results in erroneous readings.

    5G UWB/URLLC Would not be a factor here as those are small mesh-cell sites and do not radiate enough power to reach more than 2-500 feet away due to how they are designed, plus note worthy, only maybe 8 airports in the world would be within that range, and 5G UWB operates in a completely different band, in the MMW 28-35GHz range. putting it outside of this claimed issue.

    Rohde & Schwarz GmbH & Co KG have done extensive testing, developed the standards for 5G and have all the materials handy for anyone who would like to review the spectrum allocations for 5G Low and Mid Bands, which are just reallocated spectrum frequencies of 4G LTE, and operate pretty much the same as 4G LTE, just in a different band.

    • Also noteworthy 5G operates in the vertical polarity and orientation. so unless a plane is in a hard bank under 500 ft altitude, pointed right at a 5G tower to expose the transceivers directly at the tower. no cell tower emits its RF above 6.5 degrees elevation to the emitter height.

      This is why cellphones and mobile devices stop operating above roughly 1400-2000 Ft AGL and i have tested this extensively myself. Because the RF Output is very carefully aimed from the emitters themselves to a elevation range of +6.5 through -65 Degrees. their azimuth for each sectional emitter is dependent on the tower design. every cell tower design and its emitters have either 3 sectionals or 4 which are arranged in a Equilateral Triangular support system.

      each side of the triangle has the 3-4 emitters, so each side covers 120 Degrees of Azimuth. take that side and divide it by the number of emitters on that side and you get the azimuth coverage per emitter.

      so 120/3=40 and 120/4=30 Degrees per Emitter, and add all that up, and you get 360 Degrees of Azimuth around a tower with a vertical aim of 6.5 Degrees up and 65 Degrees down from the face of the emitter itself.