5 ms·

It's not obvious at all. Boeing shouldn't be using these frequencies and this has been 10 years in the making. Boeing should fix their equipment to operate with

It's not obvious at all. Boeing shouldn't be using these frequencies and this has been 10 years in the making. Boeing should fix their equipment to operate within its assigned range (+ the huge guard bands they gave them for no real reason). This is like your neighbor driving onto your lawn, and then demanding you move out of your house. They should drive right back onto their lawn.

mardifoufs 5y ago
What about older planes? I'm not sure if boeing should be responsible for retrofitting all of their older planes just because of change that happened years later.
- tssva 5y ago
  Boeing's altimeters should have always operated within the frequency bands allocated to them and been resistant to interference from other bands. These altimeters are operating outside the specification they should have met when deployed. This is an utter failure on the part of aircraft manufacturers, airlines and the FAA. They are all screaming loudly to try to shift the public perception to this being an issue created by the FCC and telecom companies.
  - NovemberWhiskey 5y ago
    >Boeing's altimeters should have always operated within the frequency bands allocated to them and been resistant to interference from other bands. These altimeters are operating outside the specification they should have met when deployed. What is your basis for this extraordinary claim?
    - jaywalk 5y ago
      What's extraordinary about the claim? The guard band between 5G and radio altimeters is ~200MHz, which is massive. If your filtering can't handle signals over 200MHz away from what you're looking at, then it's garbage filtering.
      - anfilt 5y ago
        200 Mhz may be massive for communications (especially digital encoded signals), not necessarily for radar when you sensor is receiving weak reflected signals that very likely can have a frequency shift on reflection. So radar receivers need to receive on a wider frequency band than a receiver for communications. Depending on the strength of 5G transmitters the higher order harmonics could be above the noise floor.
        NovemberWhiskey 5y ago
        Especially for FMCW applications using homodyne transceiver architectures; like you see in most civilian radar altimeters.
    - avianlyric 5y ago
      This is not an extraordinary claim, it’s how all basic radio spectrum allocation works. How else are you supposed to make sure that equipment made today won’t interfere with equipment made tomorrow if people don’t stick within their frequency allocations? The claim above is basically the equivalent of “car should have always operated on the roads that are allocated for them, and should never have been driving through empty fields”. If you’re driving your car through a field you don’t own, you don’t get to complain when someone builds a house there.
      - NovemberWhiskey 5y ago
        Do you know how a typical radar altimeter works? Do you know what the source of the specifications for radar altimeters for airborne applications is?
        avianlyric 5y ago
        What has that got to do with spectrum allocation? All radio equipment is meant to be specified to operate only within its allocated spectrum, and to handle RF noise and interference from anything outside it’s spectrum. How a radalt works is irrelevant, the allocation determines the operating parameters. If your equipment can’t operate within those parameters then it’s faulty, simple as that. Nobody would try to defend a building whose foundation crept over outside of the plot of land belonging to it. If you’re house can’t standup without putting parts of itself into your neighbours garden, then your house is faulty, not you’re neighbours home when they decide to repurpose their garden.
    - MobiusHorizons 5y ago
      How is it extraordinary? Equipment is typically required by law to operate only within its specified frequency bands. 5G spectrum was never allocated to aircraft radar altimeters. I agree that quoted suggestion lacks nuance in the history that brought us to this state, but from a technical perspective it does not seem extraordinary. More that it simply advocates a very expensive and uncooperative way to solve a problem of the commons.
      - NovemberWhiskey 5y ago
        Equipment is required to emit only within its allocated frequency bands. No-one is suggesting that the radar altimeters are emitting outside of their allocation; but there's no law that says that devices have to be immune to interference from other transmissions outside their allocated bands.
        fennecfoxen 5y ago
        There’s definitely laws that say certain equipment had to “accept” interference from lawful transmissions. You’ll find a label to that effect on every piece of 802.11 and Bluetooth gear in the US, for starters. “Immunity” is largely your own problem though.
        NovemberWhiskey 5y ago
        >There’s definitely laws that say certain equipment had to “accept” interference from lawful transmissions. You’ll find a label to that effect on every piece of 802.11 and Bluetooth gear in the US, for starters. That's specifically for unlicensed Part 15 devices ref. https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15#p-15.19(a)(3) https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A... ... the point of that wording is that unlicensed devices have no rights vs. licensed emissions.
- throwaway894345 5y ago
  If Boeing sold planes with altimeters that rely on frequencies that weren't allotted to aviation, then Boeing sold defective planes and should absolutely be responsible for retrofitting them. The fact that those frequencies are recently coming into use is immaterial. It would be different if Boeing designed their altimeters to only depend on spectrum that was allocated for aviation, but then the FCC came along and carved the 5G spectrum out of the aviation spectrum after Boeing built its planes.
- bluGill 5y ago
  Airplanes have a lifespan, older ones are mostly retired, and the rest need their radios updated to modern standards anyway. Airplanes from the 1950s normally will last essentially forever, but modern airplanes are built with lighter materials that have the downside of metal fatigue from normal flexing and so they have to be retired after so many uses. (beware of this when flying backward country airlines, it isn't unheard of for a "retired" airplane to be put back into service in a backward country - Boeing thinks they should be retired, but their standards are conservative and so there is potentially a lot of life left in the air frame before it suddenly falls apart killing everyone on board) Note, their are airplanes built today that don't have the metal fatigue issues - material selection is a complex process that each design needs to consider. I'm not sure what the 737 is made of.
  - nimih 5y ago
    What do you mean by "backward country" in this context?
    - bluGill 5y ago
      Someplace that doesn't check on things like that. There is no good guideline for that, at least not one I know of
- cogman10 5y ago
  In any other broadcasting circumstance "It'll be hard to come up to the spec we should have been following for years" would not be an acceptable excuse. They have a huge chunk of spectrum with a very wide guard band. If a TV station started leaking over another channel, you can bet that'd be shut down almost immediately, regardless of the cost to the station for putting up faulty broadcasting equipment. Boeing should be required to fix their broken electronics. Sucks to suck.
  - hasmanean 5y ago
    Tv stations do leak into adjacent bands. They contribute to the noise floor. It’s just that your real tv station broadcasts at 10,000W or whatever so it drowns out the other noise. When it comes to radar, they cannot increase the TX power and have to detect a lower RX power. Also since they are analog any interference manifests itself as a direct error. It’s like saying you should never be able to hear a whisper from your neighbours house. Obviously you can limit the amount of loud noises coming from your neighbours. You can’t silence them completely.
    - paulmd 5y ago
      > When it comes to radar, they cannot increase the TX power and have to detect a lower RX power. other radar altimeters tolerate this just fine - it is a few specific models that have problems with rejecting signals that (according to design specifications) they should easily be able to reject. > It’s like saying you should never be able to hear a whisper from your neighbours house if local code says that a house should have noise insulation sufficient that a 100db noise source located at 30 meters away should produce no more than X noise level inside the house, and a 100db noise source at 60 meters away (twice the original specification) is still significantly greater than X - then yes, your house fails to meet code. It's defective. nobody is blind to the problem of radio interference. Design specs for what level of noise needed to be tolerated were standardized in the 70s. That spec hasn't been reduced, actually it has been relaxed to over twice the original guardband specification, and certain altimeters still fail. They're defective, end of story. Replace them with the models of radar altimeters which meet the original spec, done. They exist, it's not a universal problem, it's a few specific defective models of radar altimeters. Boeing just doesn't want to ground their fleet again, and the FAA is humoring them because of regulatory capture.
heyflyguy 5y ago
What are you talking about "guard bands" ? Is there spectrum assigned alongside the radalt to ensure no crosstalk?
- leoqa 5y ago
  “Guard” is a common frequency for all pilots to listen/communicate. It’s very rarely used as intended and is mostly cat meows and fart noises.
  - addaon 5y ago
    Guard frequency (121.5) is different than "guard bands" in this context. Guard bands are, as was guessed, a frequency range at the edge of an allocation where no energy is /intentionally/ transmitted, and where received signal /should be/ disregarded. Basically it allows the reality of some frequency spillage to be accommodated between what would otherwise be adjacent frequency allocations.
  - mlindner 5y ago
    That is completely unrelated. https://en.wikipedia.org/wiki/Guard_band https://en.wikipedia.org/wiki/Guard_band
- avianlyric 5y ago
  Yes exactly that. The FCC allocated spectrum for radalts to use, then set aside an equivalent amount of spectrum (which is an insane amount of spectrum for a guard band, easily double what most uses get) above and below the radalts spectrum as guard bands that no one is allowed to use. The guard bands ensure that if there is a little spill over from 5G (which there won’t be because modern radios are better than that), or if the radalts have crappy filtering on their front ends (which it seems they do). Then nothing bad will happen, because the guard bands give everyone lots of space for sloppy engineering (which Boeing seems to be abusing)
  - p_l 5y ago
    Boeing is not abusing anything - they just published a study on the models of altimeters that were sold with their planes, in specific configurations. Similar studies are performed by Airbus, Bombardier, Dassault, Cessna, etc. etc. And FCC rules only specified transmission frequency of radar altimeters, and radio is analog and perfect filtering is close to impossible (especially with the kind of chirping signal radar altimeters use, where whole 200MHz of spectrum is spanned in single chirp)
mcguire 5y ago
I realize it's fun to hate on Boeing, but you do realize Airbus, the Airline Pilots Assns. (https://www.alpa.org/resources/aircraft-operations-radar-altimeter-interference-5G https://www.alpa.org/resources/aircraft-operations-radar-alt...), and the ICAO(https://www.icao.int/safety/FSMP/MeetingDocs/FSMP%20WG11/IP/FSMP-WG11-IP08_ICAO%20Flight%20Operations%20Panel%20and%20IATA%20%20IFALPA%205G%20problem%20statement.pdf https://www.icao.int/safety/FSMP/MeetingDocs/FSMP%20WG11/IP/...) are also concerned?
labcomputer 5y ago
I downvoted this comment for the completely wrong analogy and misunderstanding of how radio works. So wrong, in fact, that it is hard to believe it was made in good faith. Still, I am going to treat it as if it were. The problem is on the radar altimeter's Rx side, not on the Tx side. The radalt has Rx filters to reject noise on nearby frequencies. Cell towers have Tx filters to avoid broadcasting on nearby frequencies. But no real filter has 100% rejection outside the passband. That means that a 5G cell tower will broadcast some amount of energy within the spectrum defined for radalts. Also, radalts are not able to perfectly reject all energy that is outside, but arbitrarily close to their defined spectrum. A second factor is that power received by a radar falls as the fourth power of distance between a radar and the target (in this case, the ground). Tx power goes as 1/r^2. The target, having received that 1/r^2 power, then re-radiates it back to the radar, where it again falls as 1/r^2. That means radars have to be designed to detect very small amounts of power. Because physics. So the combination these factors leads to a situation where the high broadcast power of a cell tower inevitably leaks some energy into spectrum near that which radalts operate in, not all of which is effectively attenuated by the radalt's Rx filter. The small amount of energy that leaks past both filters can cause interference due to the sensitivity requirements of radalts. At a fundamental level, it was really stupid for the FCC to allocate high power transmitters in a band right next to radars. This is starting to be a pattern: See the attempted Light-Squared allocation next to GPS (for which the received signal strength on earth's surface is lower than the thermal noise floor). Based on the number of comments confidently proclaiming that radalts are somehow using spectrum they aren't supposed to, I'm starting to think that HN is being heavily astroturfed on this subject. > This is like your neighbor driving onto your lawn, and then demanding you move out of your house. They should drive right back onto their lawn. No, this is like your neighbor planting some very delicate flower near the property line and then asking you not to spray Roundup all over your property because some of it drifts onto his flowers.

mardifoufs 5y ago

What about older planes? I'm not sure if boeing should be responsible for retrofitting all of their older planes just because of change that happened years later.

tssva 5y ago
Boeing's altimeters should have always operated within the frequency bands allocated to them and been resistant to interference from other bands. These altimeters are operating outside the specification they should have met when deployed. This is an utter failure on the part of aircraft manufacturers, airlines and the FAA. They are all screaming loudly to try to shift the public perception to this being an issue created by the FCC and telecom companies.
- NovemberWhiskey 5y ago
  >Boeing's altimeters should have always operated within the frequency bands allocated to them and been resistant to interference from other bands. These altimeters are operating outside the specification they should have met when deployed. What is your basis for this extraordinary claim?
  - jaywalk 5y ago
    What's extraordinary about the claim? The guard band between 5G and radio altimeters is ~200MHz, which is massive. If your filtering can't handle signals over 200MHz away from what you're looking at, then it's garbage filtering.
    - anfilt 5y ago
      200 Mhz may be massive for communications (especially digital encoded signals), not necessarily for radar when you sensor is receiving weak reflected signals that very likely can have a frequency shift on reflection. So radar receivers need to receive on a wider frequency band than a receiver for communications. Depending on the strength of 5G transmitters the higher order harmonics could be above the noise floor.
      - NovemberWhiskey 5y ago
        Especially for FMCW applications using homodyne transceiver architectures; like you see in most civilian radar altimeters.
  - avianlyric 5y ago
    This is not an extraordinary claim, it’s how all basic radio spectrum allocation works. How else are you supposed to make sure that equipment made today won’t interfere with equipment made tomorrow if people don’t stick within their frequency allocations? The claim above is basically the equivalent of “car should have always operated on the roads that are allocated for them, and should never have been driving through empty fields”. If you’re driving your car through a field you don’t own, you don’t get to complain when someone builds a house there.
    - NovemberWhiskey 5y ago
      Do you know how a typical radar altimeter works? Do you know what the source of the specifications for radar altimeters for airborne applications is?
      - avianlyric 5y ago
        What has that got to do with spectrum allocation? All radio equipment is meant to be specified to operate only within its allocated spectrum, and to handle RF noise and interference from anything outside it’s spectrum. How a radalt works is irrelevant, the allocation determines the operating parameters. If your equipment can’t operate within those parameters then it’s faulty, simple as that. Nobody would try to defend a building whose foundation crept over outside of the plot of land belonging to it. If you’re house can’t standup without putting parts of itself into your neighbours garden, then your house is faulty, not you’re neighbours home when they decide to repurpose their garden.
  - MobiusHorizons 5y ago
    How is it extraordinary? Equipment is typically required by law to operate only within its specified frequency bands. 5G spectrum was never allocated to aircraft radar altimeters. I agree that quoted suggestion lacks nuance in the history that brought us to this state, but from a technical perspective it does not seem extraordinary. More that it simply advocates a very expensive and uncooperative way to solve a problem of the commons.
    - NovemberWhiskey 5y ago
      Equipment is required to emit only within its allocated frequency bands. No-one is suggesting that the radar altimeters are emitting outside of their allocation; but there's no law that says that devices have to be immune to interference from other transmissions outside their allocated bands.
      - fennecfoxen 5y ago
        There’s definitely laws that say certain equipment had to “accept” interference from lawful transmissions. You’ll find a label to that effect on every piece of 802.11 and Bluetooth gear in the US, for starters. “Immunity” is largely your own problem though.
        NovemberWhiskey 5y ago
        >There’s definitely laws that say certain equipment had to “accept” interference from lawful transmissions. You’ll find a label to that effect on every piece of 802.11 and Bluetooth gear in the US, for starters. That's specifically for unlicensed Part 15 devices ref. https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A/part-15#p-15.19(a)(3) https://www.ecfr.gov/current/title-47/chapter-I/subchapter-A... ... the point of that wording is that unlicensed devices have no rights vs. licensed emissions.
throwaway894345 5y ago
If Boeing sold planes with altimeters that rely on frequencies that weren't allotted to aviation, then Boeing sold defective planes and should absolutely be responsible for retrofitting them. The fact that those frequencies are recently coming into use is immaterial. It would be different if Boeing designed their altimeters to only depend on spectrum that was allocated for aviation, but then the FCC came along and carved the 5G spectrum out of the aviation spectrum after Boeing built its planes.
bluGill 5y ago
Airplanes have a lifespan, older ones are mostly retired, and the rest need their radios updated to modern standards anyway. Airplanes from the 1950s normally will last essentially forever, but modern airplanes are built with lighter materials that have the downside of metal fatigue from normal flexing and so they have to be retired after so many uses. (beware of this when flying backward country airlines, it isn't unheard of for a "retired" airplane to be put back into service in a backward country - Boeing thinks they should be retired, but their standards are conservative and so there is potentially a lot of life left in the air frame before it suddenly falls apart killing everyone on board) Note, their are airplanes built today that don't have the metal fatigue issues - material selection is a complex process that each design needs to consider. I'm not sure what the 737 is made of.
- nimih 5y ago
  What do you mean by "backward country" in this context?
  - bluGill 5y ago
    Someplace that doesn't check on things like that. There is no good guideline for that, at least not one I know of
cogman10 5y ago
In any other broadcasting circumstance "It'll be hard to come up to the spec we should have been following for years" would not be an acceptable excuse. They have a huge chunk of spectrum with a very wide guard band. If a TV station started leaking over another channel, you can bet that'd be shut down almost immediately, regardless of the cost to the station for putting up faulty broadcasting equipment. Boeing should be required to fix their broken electronics. Sucks to suck.
- hasmanean 5y ago
  Tv stations do leak into adjacent bands. They contribute to the noise floor. It’s just that your real tv station broadcasts at 10,000W or whatever so it drowns out the other noise. When it comes to radar, they cannot increase the TX power and have to detect a lower RX power. Also since they are analog any interference manifests itself as a direct error. It’s like saying you should never be able to hear a whisper from your neighbours house. Obviously you can limit the amount of loud noises coming from your neighbours. You can’t silence them completely.
  - paulmd 5y ago
    > When it comes to radar, they cannot increase the TX power and have to detect a lower RX power. other radar altimeters tolerate this just fine - it is a few specific models that have problems with rejecting signals that (according to design specifications) they should easily be able to reject. > It’s like saying you should never be able to hear a whisper from your neighbours house if local code says that a house should have noise insulation sufficient that a 100db noise source located at 30 meters away should produce no more than X noise level inside the house, and a 100db noise source at 60 meters away (twice the original specification) is still significantly greater than X - then yes, your house fails to meet code. It's defective. nobody is blind to the problem of radio interference. Design specs for what level of noise needed to be tolerated were standardized in the 70s. That spec hasn't been reduced, actually it has been relaxed to over twice the original guardband specification, and certain altimeters still fail. They're defective, end of story. Replace them with the models of radar altimeters which meet the original spec, done. They exist, it's not a universal problem, it's a few specific defective models of radar altimeters. Boeing just doesn't want to ground their fleet again, and the FAA is humoring them because of regulatory capture.

heyflyguy 5y ago

What are you talking about "guard bands" ? Is there spectrum assigned alongside the radalt to ensure no crosstalk?

leoqa 5y ago
“Guard” is a common frequency for all pilots to listen/communicate. It’s very rarely used as intended and is mostly cat meows and fart noises.
- addaon 5y ago
  Guard frequency (121.5) is different than "guard bands" in this context. Guard bands are, as was guessed, a frequency range at the edge of an allocation where no energy is /intentionally/ transmitted, and where received signal /should be/ disregarded. Basically it allows the reality of some frequency spillage to be accommodated between what would otherwise be adjacent frequency allocations.
- mlindner 5y ago
  That is completely unrelated. https://en.wikipedia.org/wiki/Guard_band https://en.wikipedia.org/wiki/Guard_band
avianlyric 5y ago
Yes exactly that. The FCC allocated spectrum for radalts to use, then set aside an equivalent amount of spectrum (which is an insane amount of spectrum for a guard band, easily double what most uses get) above and below the radalts spectrum as guard bands that no one is allowed to use. The guard bands ensure that if there is a little spill over from 5G (which there won’t be because modern radios are better than that), or if the radalts have crappy filtering on their front ends (which it seems they do). Then nothing bad will happen, because the guard bands give everyone lots of space for sloppy engineering (which Boeing seems to be abusing)
- p_l 5y ago
  Boeing is not abusing anything - they just published a study on the models of altimeters that were sold with their planes, in specific configurations. Similar studies are performed by Airbus, Bombardier, Dassault, Cessna, etc. etc. And FCC rules only specified transmission frequency of radar altimeters, and radio is analog and perfect filtering is close to impossible (especially with the kind of chirping signal radar altimeters use, where whole 200MHz of spectrum is spanned in single chirp)

mcguire 5y ago

I realize it's fun to hate on Boeing, but you do realize Airbus, the Airline Pilots Assns. (https://www.alpa.org/resources/aircraft-operations-radar-altimeter-interference-5G https://www.alpa.org/resources/aircraft-operations-radar-alt...), and the ICAO(https://www.icao.int/safety/FSMP/MeetingDocs/FSMP%20WG11/IP/FSMP-WG11-IP08_ICAO%20Flight%20Operations%20Panel%20and%20IATA%20%20IFALPA%205G%20problem%20statement.pdf https://www.icao.int/safety/FSMP/MeetingDocs/FSMP%20WG11/IP/...) are also concerned?

labcomputer 5y ago

I downvoted this comment for the completely wrong analogy and misunderstanding of how radio works. So wrong, in fact, that it is hard to believe it was made in good faith. Still, I am going to treat it as if it were. The problem is on the radar altimeter's Rx side, not on the Tx side. The radalt has Rx filters to reject noise on nearby frequencies. Cell towers have Tx filters to avoid broadcasting on nearby frequencies. But no real filter has 100% rejection outside the passband. That means that a 5G cell tower will broadcast some amount of energy within the spectrum defined for radalts. Also, radalts are not able to perfectly reject all energy that is outside, but arbitrarily close to their defined spectrum. A second factor is that power received by a radar falls as the fourth power of distance between a radar and the target (in this case, the ground). Tx power goes as 1/r^2. The target, having received that 1/r^2 power, then re-radiates it back to the radar, where it again falls as 1/r^2. That means radars have to be designed to detect very small amounts of power. Because physics. So the combination these factors leads to a situation where the high broadcast power of a cell tower inevitably leaks some energy into spectrum near that which radalts operate in, not all of which is effectively attenuated by the radalt's Rx filter. The small amount of energy that leaks past both filters can cause interference due to the sensitivity requirements of radalts. At a fundamental level, it was really stupid for the FCC to allocate high power transmitters in a band right next to radars. This is starting to be a pattern: See the attempted Light-Squared allocation next to GPS (for which the received signal strength on earth's surface is lower than the thermal noise floor). Based on the number of comments confidently proclaiming that radalts are somehow using spectrum they aren't supposed to, I'm starting to think that HN is being heavily astroturfed on this subject. > This is like your neighbor driving onto your lawn, and then demanding you move out of your house. They should drive right back onto their lawn. No, this is like your neighbor planting some very delicate flower near the property line and then asking you not to spray Roundup all over your property because some of it drifts onto his flowers.