Another Tuesday; Another 5G C-Band Debacle Delayed (Updated)


The telecom industry, specifically AT&T and Verizon, have again backed off from plans to deploy 5G C-Band broadband technology at midnight Tuesday (January 18), at least in areas close to between 50 and 80 airports. The FAA and the airline industry continue to maintain that instrument approaches reliant on radar/radio altimeters are not safe enough in light of a lack of testing.

AT&T released a statement that said, in part, “At our sole discretion, we have voluntarily agreed to temporarily defer turning on a limited number of towers around certain airport runways as we continue to work with the aviation industry and the FAA to provide further information about our 5G deployment, since they have not utilized the two years they’ve had to responsibly plan for this deployment.”

The frequencies used by the low-power (1-watt) altimeter transmitters have remained buffered in the frequency range, until the FCC enabled telecom providers to acquire the 5G C-Band wireless telephone/broadband signals in the 3.7 to 3.98 GHz range. The FAA claims it does not have the resources to complete adequate testing to approve the radar altimeters’ performance with cellular signals operating that close in the frequency band.

Accordingly, the FAA has issued provisional Notices to Air Missions (NOTAMs) blocking the use of Autoland, Category II and Category III approach capability in aircraft that rely on radar altimeters for the procedures. Thus, instrument approaches at up to 80 affected airports would be limited to Category I instrument landing system (ILS) approaches, typically 200-foot ceilings and one-half-mile visibility.

Airline executives have raised the alarm that the NOTAMs would cost millions in lost revenue from canceled flights and cause systemic chaos, stranding untold numbers of passengers. The FAA and airlines are demanding clear zones within two miles of affected runways at the airports impacted by the 5G deployment.

Both industries say they continue to work toward a viable solution to the issue.

Update: According to a statement issued by the FAA on Wednesday, it has issued approvals that “allow an estimated 62 percent of the U.S. commercial fleet to perform low-visibility landings at airports where wireless companies deployed 5G C-band.” To date, the agency has cleared five altimeters, but noted that flights at some airports may still be affected even with the approvals.

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Mark Phelps is a senior editor at AVweb. He is an instrument rated private pilot and former owner of a Grumman American AA1B and a V-tail Bonanza.

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  1. The perception of nuisance alerts means that the unambiguity of a radalt tone is already lost…in a past life, when the radalt went off, you reacted first, especially if it was unexpected. Now I fear the first reaction will be to swat it off after one too many “cried wolf” alerts.

  2. I always thought that one of the primary reasons for the existence of the Federal Communication Commission is to organize, responsibly grant/sell/withhold licensing and maintain the radio frequency spectrum. So, they can’t just leave it to the manufacturer/service providers (sound familiar?). WTF are they doing about this?

  3. They published a NOTAM for this at Chicago O’Hare. No CAT II approaches, among others. While not an every day approach, when weather goes below mins for CAT I, everyone is doing CAT IIs. This is going to cause massive disruptions if something isn’t figured out soon.

  4. “The FAA claims it does not have the resources to complete adequate testing to approve the radar altimeters’ performance with cellular signals operating that close in the frequency band.”

    Well, gee, can’t the White House throw some bucks their way?

  5. Silly me. I was under the impression that the FCC was responsible for assuring that any frequency they granted rights to, was safe to operate without interference either TO adjacent frequency operations, or FROM adjacent operations. In other words, THEY, or the people who were buying/leasing the frequency bands are the ones that are responsible for proving they can operate without interference. Since the FAA, the military, and numerous aviation alphabet groups objected to the use of C band over two years ago, AT&T and Verizon should have been required to prove there was no interference, not the FAA. Granted, the FAA should have provided a test protocol for any study. Also, at this point, if the telecoms want that frequency space that bad, let them pay for installing updated radar altimeter systems at least on affected commercial and business aircraft. After all, they stand to make billions in profit from the frequency use. Just my two cents…

    • Why should the telecom companies be forced to pay? the frequencies they are using are adjacent not overlapping the radar altimeter ones. The FAA certified and approved radar altimeters that are sensitive to interference from frequencies outside of their assigned band. Granted this was years ago when there wasn’t anything on the adjacent band. Basically the manufacturers of the radar altimeters went cheap and decided they didn’t have to make altimeters that were only sensitive in their assigned operating band. Unless there was some kind of guarantee from the FCC that those bands would never be used this whole thing is the fault of the manufacturers of the radar altimeters and the FAA.

    • In the UK, Ofcom said the country had had 5G deployments and other services in the bands near to radio altimeters for years and there have been no known cases of interference.

      Similarly, other countries are already using these frequencies for 5G and other wireless services with no reported incidents of interference to aviation equipment.

      • Error!

        Many countries do not have such transmissions as close to radalt frequencies, do not have power as high as US allows, and have antennas tilted down a bit compared to US installations. (Directional antennas thus even a small tilt greatly reduces ae of concern.)

        You might do some homework including

        You’d learn from that obscure thing called Internet that the industry has cleared two brands of radio altimeters, and 45% of the airline fleet in the US. You’d learn that how radalt data is used in landing matters – the 787 makes more use of it for air-ground logic than most other airliners thus is of concern.


      • Reading the FAA pages I point you to in a message sysop has not yet approved, you’d find a link to RTCA Paper No. 274-20/PMC-2073 which describes the problem.

        Note that radalt RX sensitivity is very high because TX power is very low. And that RX mask is quite broad.

        Note that aircraft may have a roll attitude pointing toward wireless TX thus widening effective scan angle.

        There are two common methods of operation of radalts: pulse and FMCW, with different vulnerability.

        And note that ambulance helicopters are of concern because they operate close to the ground in dense urban areas – to hospital helipads.


  6. I have seen this before in other fields. Two sides butting heads, when there is a simple answer. DO SOME TESTING.

    Pick an airport with Cat 2 and Cat 3 approaches, have them up a 5G cell in the worst case location and fly some approaches in VFR conditions. This could show massive problems or it could show very little. If very little or none, yes more testing is needed.

    But the telcom companies and the airlines should partner to get this testing done. Instead of everyone pointing fingers and shouting.

  7. I’ve seen this interference problem manifest in another way. National Guard helicopter leaving an air base and passing over a C Band satellite receiver dish antenna which was carrying live program audio for a radio network. This was a regular problem at that station. The satellite C band receiver would become overwhelmed by the near band signal and loose it’s sensitivity and become unlocked which means no audio during the passage of the helicopter. A waveguide type filter at the LNB of the receiver antenna made the problem go away.
    Now the FCC has completed a satellite C Band frequency repack where broadcasters and satellite service providers have moved the spectrum some to accommodate the frequencies that the FCC had sold to the wireless cellular providers for 5G.
    Now broadcasters are having to purchase antenna receiver LNBs with 5G filters and possibly other add on bandpass filters to be used if necessary.
    I haven’t installed them yet at my employ but I have to believe that the wireless 5G services will also get slammed by the radar altimeters passing over and that nobody at either FCC or FAA have any idea of which way is up or down.

    • How likely is that to be an issue? I’m asking because it sounds like you have access to better information on this than I do. From what I have seen, radalt output power is low, and the 5G receivers have lower sensitivity than a receiver used for satellite communications, so the interference threat seems largely one-way due to higher 5G output power and more sensitive (and less heavily filtered) radalt receivers.

      • Sir my cellular phone’s present received signal level on LTE is -118dBm.
        The greater the negative number the lower the signal.
        The phone and data work fine at this low level.
        And in RF communications this is a very low signal.
        We can only wait and see. Perhaps the military helicopter uses a higher power transmitter than other aircraft for radar altitude.

        • But closer to the transmitter signal level may be higher.

          Power is a factor, in Europe 5G antennas are not as strong.

          The problem helicopters face is they fly closer to transmitters, including ambulances to helipads at hospitals in cities. The RTCA study talks of many phone adding up to higher level of interference potential.

          The problem with helicopters was recognized years ago in the general l interference subject called HIRF.

          In the HIRF debates was an illustration of the need to keep perspective and actually calculate. One transmitter of concern was used to contact deep space probes, quite powerful. But beam size was quite small near earth so impact on an aircraft would be small.

          • Yes when a receiver is in the near field of a transmitter it can become desensitized which ruins it’s ability to continue to accurately receive during that period. You probably have experienced this without thinking about it if you listen to FM broadcast radio in your car and drive through the RF near field of another FM radio transmitter on a different channel. It will cause problems like noise on the analog and lack of HD lock on the digital side of the station that you are listening to.
            So cellular site receivers and cellular phones all operate with very high sensitivity receivers. Interference from aircraft altimeters will be transient. With TCP data packets they will get retransmitted if lost by dropouts and the data reassembled. With UDP packets and packetized voice service you will get drop outs in your conversations or live streams that can’t be corrected for.
            Another thing to consider is that these 5G signals are not expected to be received line of sight. They are reflected and dispersed in many directions by terrain and obstructions. Radio altimeters have their primary signal pulses reflected all over the place as well but the receivers on aircraft use the first ground reflection to calculate.

      • Physical blockage is not a problem. The antenna beam width of the SAT antenna is extremely narrow and the speed of an aircraft transiting that is just in the blink of an eye.
        Our radio station got slammed for a good long period during the aircraft both coming and going. It was a real thing that happened over and over again.

  8. Follow the money. FCC chair Ajit Pai, former lawyer for Verizon, appointed by the prior administration, is a relentless proponent of tech in all circumstances. Small wonder that FCC and the prior administration ignored concerns raised by the FAA and aviation alphabets for several years to push through the spectrum auction in the waining months of the previous administration. Gee, wonder how that happened? And, the present administration seems flummoxed by the situation. Here we are…