FAA says 5G could impact radio altimeters on most Boeing 737s
reuters.com
reuters.com
Am I missing something?
If a rancher buys a plot of land from 34.42°N to 34.44°N to graze his cattle on, but in actual fact grazes his cattle all the way from 34.37°N to 34.47°N. Then a farmer buys a plot of land from 34.37°N to 34.398°N to grow wheat on. Does the rancher still get to herd his cattle down to 34.39°N to feed his cattle? The cattle have to eat, after all, and cutting down the grazing land by 30% could cause some cattle to starve to death. And the rancher has a vested financial interest in ensuring his cattle are well fed, and that wheat is good eating. And the rancher has always been grazing his cattle there, what right does the farmer have to till the soil on the racher's grazing land? And we, the American public, have the right to buy beef. Why should the farmer purchasing 34.37°N to 34.398°N interfere with my ability to buy a steak?
Does any of this make any sense to anyone?
Unless there's additional information I'm unaware of, it seems as if the design and/or manufacture of the radar altimeter is not fit for purpose. Using 3.7GHz to 3.98GHz for 5G doesn't break the radar altimeters; the radar altimeters are already broken and must be fixed or grounded, because the equipment is broken and unsafe.
If 5G equipment is emitting outside of its allocated 3.7-3.98GHz spectrum then the FCC needs to drop a brick on that of course.
[1] https://www.nolo.com/legal-encyclopedia/neighbor-built-fence...
De facto possession of spectrum was heavily litigated in the early days of radio. There basically is none (not legal advice!), essentially no one has a claim on spectrum in the USA that is not assigned or regulated by the FCC. You have to sign away any claim to spectrum from before the establishment of the FCC to get a ham license or similar radiotelephone licenses. Nobody is around anymore that was operating then anyway. The language is blandly bureaucratic but in context that is what it means: "The Applicant/Licensee waives any claim to the use of any particular frequency or of the electromagnetic spectrum as against the regulatory power of the United States because of the previous use of the same, whether by license or otherwise, and requests an authorization in accordance with this application."
There is probably some similar language in the applications for other licensed bands.
Your analogy is a great demonstration why reasoning-by-analogy fails, by the way.
Keep in mind these sensors were designed and approved long before the FCC allocated this spectrum above this range to 5G. 200 Mhz may be massive for communications, but not that is not entirely true for radar.
RFI is a problem in these spaces [1]. It's been a problem for many years, and is an increasing one.
[1] https://www.researchgate.net/publication/283760070_The_Threa...
Franky speaking, everybody here is talking out of their asses, and just rehashing bullshit that they get told. I'll lowbrow dismissal that all day long because it doesn't deserve and inch more of effort.
This whole discussion has a really low SNR
Additionally, lot these weather radars are not trying to achieve same level of accuracy as an altimeter. If the weather formations ones monitoring is off by a little bit, but overall the data is close it's fine. Similar thing with a lot maritime radar, ships are not moving that fast so you also have a lot more time to average out the data. If an altimeter when landing is off by too much can cause a lot problems, especially when you factor in the speeds of an airplane it's you have less time to average out noise or doing other things to filter out spurious noise. Edit: Also one other thing about maritime radar there nowhere as much interference once you get outside ports or areas near land.
Also it's not just Boeing here having issues, airbus also along with Boeing has brought this to the attention the FAA. The frequency bands in other countries for 5G tend to be farther away as well from the frequencies used by altimeters so it's not been issue in other countries. It only seems to be handful of air-frames that effected.
Secondly, NOAA have been concerned about 5G, particularly near 24Ghz, again for possibly interfering with radar.
All I was saying is radar is a lot more sensitive to the noise floor and if suddenly that noise floor is higher I am not surprised some equipment will have issues depending on it's use case. Especially, when things were designed long before these new spectrum allocations.
See my post about international radio regulations, the 5G service should not have been allocated if it was going to interfere with radar altimeters as that was (and still is) a 'going' service and it takes precedence under international radio treaties.
Thus, an aircraft from a country that's not under US jurisdiction expects to be able to land in the US without its radar altimeter being jammed by some unexpected local service. (It stands to reason that the safety of an aircraft that travels across international borders should not be endangered because of inference to its navigation equipment.)
This is the precise reason why international radio regulations exist! Under the treaty the 'interference' rules apply to ALL radiocommunication services.
If such regulations (standards) are deemed 'old' then they have to be changed at an ITU WRC meeting in Geneva and the item must appear on the meeting's agenda some years before said meeting takes place to give all countries adequate time to respond (as I mentioned elsewhere, I was once involved in that process).
> Radar in general is more sensitive to noise.... The noise floor is quite a bit higher before it becomes unusable for communications compared to radar
This is not true. A radar has the huge advantage of knowing what signal was sent and only looks for returns that are similar- the FMCW radars in question often mix the return with the originating signal, and outside interference just doesn't cohere and won't affect the result unless the interference is very high power. Radars do not need to look at a wider band of spectrum, reflections do not change the frequency and the Doppler shift a radar altimeter (looking straight down) needs to accommodate is minuscule. A radar that can't handle noise is poorly designed, not that they are inherently susceptible to noise. Radar does require "high" transmit power to easily detect returns, but they can be robust to noise. A radar (including RA) can integrate over a relatively large window if needed and detect with an SNR <1 if it's designed that way.
Whether the old 737 RA was properly designed and can handle the interference, or if they took shortcuts because saving a buck took precedence is a different discussion than the (incorrect) generalities about radar presented in the above comment. Whether the existing RAs can be retrofitted with better filters for cheaper than lobbying the FCC is also unclear, but we know what approach the airlines are attempting right now.
I agree with the general tenet of your post but do we know what the status of the radar's RX's front end is like in practice?
From my experience, many of the front ends of older radar receivers are primitive by comparison with today's state of the art in that they have very bad crossmoduation figures (basic diode mixers etc.).
The gap is the same size as the entire allocation, and the frequency difference is more than 4 percent. That's massive.
> Radar needs to look at a wider band of spectrum as things will get shifted more from reflection and such.
If you skew a radar signal by a thousand miles per hour, isn't that around 2 parts per million? Am I missing an effect here?
Edit: I will add the a fair amount of interference by multi path return can be mitigated by making the transmitter and receiver shielded from other directions and designed to be highly directional. This also is generally not to hard to do for an altimeter since the datatum one is measuring after all is just elevation over a small area, compared to something like radar for topography that wants to cover a large area.
And so far, despite weeks of work, no one has shown anyone is breaking the noise generation limit.
What confuses me here is exactly the FAAs safety requirements: they've said there could be a problem. But they've also not done any research to assess it. And they're not grinding any planes. So they apparently aren't that bothered by safety!?
There is ongoing body of work, done internationally, for several years now. They aren't grounding planes because there's no operational need to right now - worst case expect a lot of canceled flights and maybe Southwest going bust as their scheduling flaps too much (also, USA is a bit lucky in having lower need for Category II or worse approaches than some other countries).
And as someone else mentioned in comments, there are already issues cropping up with malfunctioning 5G transmitters despite 400MHz guard bands...
Here is the industry research, presented two years ago:
https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
Note the telco industry have attacked and politicized the research, but they have not offered up their own data to back up their claims. The aviation industry is on much stronger ground here.
And as another commenter put it so eloquently, the aviation industry assumes something is dangerous until proven safe, not that something is safe until proven dangerous.
Douglas Hofstadter would like a word with you.
Aircraft flying over C band satellite dishes (what used to use the current 5G band) used to cause interference to those dishes. In that case the problem was that the transmitter was mobile. Now the C band satellite people will have to fight interference from 5G transmitters in what remains of their band.
That's part of the reason 5G is such an issue, despite the ostensibly-large guard band. You need really good filters on the cellular 5G equipment to make sure it doesn't leak into the radar band.
I think that's specifically true when you're pointing a radar at an aircraft, but is not true for radar altimeters.
When you're pointing a radar at an aircraft, the angular size of the aircraft is 1/r^2, so 1/r^2 of the emitted radiation hits the aircraft. Once emitted from the aircraft, the angular size of radar receiving dish is 1/r^2, so 1/r^2 of that radiation is detected.
With a radar altimeter, you're pointing the radar at the ground. The angular size of the ground is 50% of the sphere, whether you're one foot above the ground or 100,000 feet. (...ok, maybe it's like 49.5% of the sphere...) As long as you're pointing it down-ish, 100% of the emitted radiation hits the ground. There is only one 1/r^2 relationship, on the return leg.
This fixed angle paints a larger and larger circle as altitude increases. If you double your altitude, you quadruple the size of the surface that's reflecting radar back at you.
A bunch of stuff cancels out and you end up with 1/r^2 at the receiver, which is what we started with.
But they’re not broadcasting to the whole sphere either, because the radar instrument is not an isotropic radiator. That antenna has gain. It’s louder / more sensitive in a specific direction. Probably by a lot. You can’t make perfect antennas, but you don’t need any signal at all from most of the sphere, so you can gain many decibels.
The angle of the beam you do have is probably fixed, and being fixed would imply that the area swept by the core of the beam is indeed proportional to the square of the altitude. But I don’t think two trips through an n^2 distance is n^4 unless I’m missing some of the physics. Shouldn’t it be (2n)^2 and this still proportional to the square of the altitude not to the hypercube? (And affected by scattering and bad reflectivity from the terrain, which seems likely to be independent of altitude?) This is different for detecting random entities in free space where most of the first n^2 trip really is lost.
So it’s like you say but for different reasons??!?!
As I keep repeating here, if excessive or debilitating interference is being experienced between services under normal operating conditions then there has been a failure of Spectrum Management planning - absolutely no question about it.
OK, we know such interference has happened, so who was responsible for the planning fuck-up?
I've no argument about filters, RFI etc., what most are saying about the engineering issues makes sense.
My argument is that the spectrum planning has failed and that much of the reason can be put down to deregulation in the 1980s when many governments essentially washed their hands of Spectrum Management (succumbed to commercial pressures and overly loosened engineering standards and now we're paying the penalty).
It seems to me (given the international nature of the problem with non-US registered aircraft flying into US airspace, etc.) that we need to go back to the core of the problem and acknowledge these past 'regulations' errors before the problem can be fixed properly.
Perhaps all radar altimeters will have to be changed (respecified with much tighter filters, better intermod figures, etc.) but given the fuck-up who should pay? After all, it's not the FAA's fault nor that of the aircraft industry (see my comments in other posts about the ITU and WRC).
As I see it, this is a political issue, not a technical one.
this is the white paper that the FAA bases their concerns on https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
that is the issue they are raising
I have run the numbers and there is no way even at phone full power that it can interfere unless it was less than 2m away even then it would have to be free space, etc.
the body losses, airframe, antenna back scatter all taken into account, very very unlikely unless the radar bandpass filters are from the 1960's
Were filters particularly bad in the '60s? If you claim to have run the numbers you will have to reveal your assumptions.
The numbers are in the doc i posted.
If Boeing needs 3.7GHz-5GHz in order to safely operate their aircraft, then Boeing needs to purchase and own the 3.7GHz-5GHz band. If they only want to pay for 4.2GHz-4.4GHz and nothing but 4.2GHz-4.4GHz, but squat on 3.7GHz-3.98GHz they can pound sand.
At the time these units were built, the filtering was sufficient to guard against the known adjacent users of the band (low-power satellite signals). Neither the FCC or the FAA set performance standards to suggest otherwise. Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz - outside a few specialized uses, it's a terrible band for wide-area communication unless somebody is motivated enough to build tons of towers...which the cell companies suddenly are.
We can agree that the filters are garbage by modern standards, but they were considered adequate at the time the units were built based on the circumstances.
At least I know why cell service at the airport is awful.
Because at the time the equipment was bought, it met every applicable federal standard. This would be unfair to the owners who had no way of knowing about the issue.
Also, in nearly every other case I can think of when spectrum changes, the FCC grandfathers in owners of legacy equipment.
> At least I know why cell service at the airport is awful.
I don't think that's at all related, given that we just started rolling out 5G. Plus the bands in question don't travel through walls very well. :/
At least in Europe, there is precedent that modern use of frequency assignments make older equipment illegal to operate. 4G and 5G have heavily eaten into the frequencies used on stage for event equipment - microphones, IEM, that sort of thing. Many, many pieces can‘t be legally operated anymore, and it‘ll probably be the same in a few years time with the current-gen devices (although I hope I can swap crystals if needed and keep using my stuff).
Radio bandwidth is a scarce resource. If the radio altimeter is transmitting well outside of its boundaries and it creates problems (for any of the parties requirements), it’s the radio altimeters that need fixing. Even if it is expensive to do so.
Also, the FAA has no way of knowing if a particular aircraft operator is using a radio altimeter or not. Even if I have one installed, maybe I chose to switch it off. It's also possible I'm using it for situational awareness only (which is still allowed) and not using it to descend below legal approach minimums.
"Airbus has issued Flight Operations Transmission 999.0002/22 (01/10/2022) which describes the currently understood effects of radar altimeter anomalies. Guidance is provided for A320 family, A330, and A340 aircraft for handing these anomalies.
"Embraer Flight Operations Letter 170-001/22 and Operational Bulletin 170-001/22 (01/02/2022): Describe the possible effects of C-Band 5G interference on its E170, E175, E190, and E195 aircraft.
"The FAA has developed a process by which better performing radar altimeters that are able to reject 5G interference can be approved to operate without regard to the AD and NOTAMs. These Alternate Methods of Compliance (AMOC) approvals will be specific to a combination of aircraft model and radar altimeter model. The method of approval will take into consideration the performance of the aircraft/radar altimeter combination, as well as the location and power of the 5G transmitter in the vicinity of the airport. Therefore, the AMOCs are being issued with a list of airports where they are effective. As of 1/25/2022, FAA has approved AMOCs for several models of radar altimeters, installed on Boeing 717, 737, 747, 757, 767, 777, 787, and MD-10/-11; Airbus A220, A300, A310, A319, A320, A321, A330, A340, A350, and A380, Embraer 120, 170, and 190, all Canadair CRJ aircraft, some DeHavilland Canada DHC-8, and some ATR aircraft. These AMOCs are limited to certain airports and specific models of radar altimeters. Pilots should ensure that they have AMOC documentation for their aircraft and airport (e.g. in a dispatch release) before operating at an airport without regard to the 5G AD/NOTAM."
https://www.alpa.org/resources/aircraft-operations-radar-alt...
If Airbus has the same problem, then ground Airbus too.
> Boeing doesn't even make the avionics in question. Some of the manufacturers don't even exist anymore. It's not clear who would pay,
Surely when the parts break, they are fixed, and if they are not fixed, then the plane is either grounded or flies in conditions such that the equipment is not required. There is a somebody who repairs, services, or replaces broken parts. These parts are broken. So that somebody fixes it.
> or how you'd enforce it.
You'd enforce fixing this broken part the same way you'd enforce fixing any other broken part. When the FAA finally got around to deciding that MCAS was in fact broken, they grounded the 737 MAX until it was fixed.
Everybody's acting like it's not a big deal that this equipment can't handle a signal that is more than 220MHz away from their nominal operating frequency. Certainly if Hasbro wanted to sell Batman(TM) BatWalkie BatTalkies, but they were rendered inoperable by another signal that far from their operating frequency, the FCC would deny the device its operating license and it would be pulled from the market.
> Nobody expected at the time we'd be blasting high-power omnidirectional signals everywhere at 4 GHz
Infrastructure 5g antennas are directional. The mobile devices themselves are omnidirectional, but those are very low power devices.
As I've point out in my post, why on earth wasn't all this sorted out before 5G was allocated the frequencies.
It seems to me that the the powers behind mobile services have railroaded themselves into these frequencies and that the FCC etc. haven't had the gumption to sort it out beforehand.
Ah, yes. The best thing you can have is tribal mentality in your government departments. Where instead of cooperating to sort problems out you just say "fuck everyone else" and press onward.
What do you mean by 'bad' receivers?
Spectrum management, irrespective of country, sets the parameters of every radiocommunication service by notional equipment standards - here that would be the typical intermodulation figures for radar receivers, inter alia.
The FCC and ITU through WARC/WRC - World Radiocommunication Conferences would have been aware of notional equipment standards for radar altimeters at the time the spectrum was allocated (equipment must comply with the standard or it be deemed out of spec - non compliant).
Note: adjacent services must consider interference to their adjacent services, etc. The standards associated with any service can only be deemed old or 'changed' at WRC conferences specifically to avoid the situation we now have here. The real question is 'who fucked up' - i.e.: did not abide by WRC rules (the international treaty/agreement obligations).
Remember, here international rules are paramount BECAUSE aircraft licensed in other countries that land on US territory also have to meet the same international standards for their radar altimeters as those of the US fleet - it has nothing to do with receivers being 'bad').
FYI: https://en.m.wikipedia.org/wiki/World_Radiocommunication_Con.... Note: the ITU deems that the FCC IS responsible for radio regulations within the USA.
Fair, but if we are to expect a certain level of "drift" outside of designated bands, does that mean that the gap between allocated bands should increase?
That is to say, if precision is an issue, what the most effective solution to deal with that lack of precision? From the sounds of it, the technology is unable to comply with the bands allocated, so the regulations around how those bands are distributed should be far more strict, right?
It's a matter of understanding what the analogy is giving you. In many cases, as above, it's merely a foothold, a way of getting started understanding what something is through partial identification with something already known. From that point, the differences between the two can be clarified.
You can think of it in terms of compressing descriptions: let's say you need to describe an SUV to someone; you could start by saying "it's like a truck but [...]," and remove a lot of the redundancy you'd get by starting from scratch.
AFAICT people who think there's something wrong with reasoning-by-analogy are analyzing it with the false assumption that people are just doing "X is like Y" rather than "X is like Y EXCEPT [...]," while also having an understanding on some level of the imprecision/limits of the partial identification.
That people are out there reasoning with analogies thinking they form perfect, limitless mappings between the domains involved seems like an imaginary problem.
I hate reasoning-by-analogy in general but in this case it sounds fine to me. Boeing are grazing their cattle on someone else's land - they don't get squatters rights because no one else was using it at the time when they built their fences. Because it was contractors that built the fences and Boeing didn't perhaps know they were using someone else's land then they should get a little time to move the cattle - or the FAA/FCC can arrange a deal and give the telecom companies some new land - but it's Boeings problem.
It all does sound a bit silly though. I will say I wish the FCC was as happy handing spectrum/power to unlicensed users as it is to what are nearly exclusively Qualcomm customers.
a rancher allowing his cattle to graze outside of his allowed land doesn't result in a fiery crash that kills hundreds of people.
you're right, the planes are in the wrong and they should be fixed. but that's kind of not the point.
Postpone the 5G allocation, make the altimeter manufacturers/users pay market price for the spectrum to those that would have gotten it allocated until they can return the spectrum, and also pay a fine to the government for using spectrum not allocated to them (in the past, current and future breach covered with the rent mentioned before).
And give some timeframe by which spectrum must be returned.
Then the FCC should proceed with the rollout of this allocation and let the clowns at Boeing and the FAA handle the fallout.
However, folks are now unhappy because that means no Cat II/III approaches, which means airliners can't land in fog or bad weather... which means significantly more airline delays while all this gets sorted out and equipment gets recertified or upgraded. Consequences.
(Also, fwiw, the avionics aren't built by Boeing, and this is not a Boeing-specific issue. It impacts other aircraft from all manufacturers.)
In that it's mostly a US-issue (Europe has much better protection in this area, i.e. that 5G antenna must be directed downwards, the 787 is the biggest issue, as those are doing international flights with other carriers to US airports.
A220 is exclusively Delta in the US I believe.
It's NOT their fault!, See my other posts about the ITU, WRC and international radio treaties.
This issue has more to do with Spectrum Management planning failures and goes back as far as the 1980s when governments washed their hands of the matter and 'deregulated' spectrum matters because of commercial pressures. Moreover, they loosened the engineering (interference) specs now we're paying dearly for the fuck-ups.
You work with providers to measure impact and to reduce interference around airports. You issue NOTAMs (Notice To Air Missions) to all pilots know where this 5G interference is known to be a problem, and you wrap it all up with AD (Airworthiness Directive) for the 737 itself which specifies that those NOTAMs apply directly to the equipment on this make and type of aircraft.
[0]: https://public-inspection.federalregister.gov/2022-03967.pdf
Did the FAA say this is what's happening for sure? If so that answers a lot of questions I've had because like you said they are on different parts of the spectrum so it should not be an issue unless something is operating out of spec.
The FCC allocated a specific band for radar altimeters to transmit in. The FCC only specified rules on transmission, and the radar altimeters are 100% compliant with the FCC rules and only transmit within their assigned band.
The FAA published TSO-87C, which is the technical spec for the radar altimeters. But this also just covers transmission and performance. There's nothing in this spec about rejecting external interference. The radar altimeters are compliant with this spec as well.
The problem is on the unregulated receive side. All radio signals have some amount of bleed-over into adjacent bands due to harmonic interference. Historically, the adjacent frequencies were used for low-power satellite communication, and the manufacturers added enough filtering to protect against the harmonic interference from these low-power stations. They did not anticipate a high-power (5G) signal in those adjacent bands, and nothing in the FAA/FCC specifications protected against it either.
So it's not that the radio altimeters are "using" the adjacent bands, but the receive filtering is (in some cases) insufficient to account for the new (louder) users of the adjacent bands.
The FCC really wants to proceed with the 5G rollout. The FAA really wants to make sure aircraft don't crash. They do not agree with each other on this, so they each proceeded in the only way they administratively could...
The FCC continued with the 5G rollout, the the FAA recently banned use of approaches requiring a radio altimeter until each individual model can get recertified or upgraded - and the public will just have to tolerate additional travel delays for the next couple years as a result.
FCC was warned by industry groups but dismissed the warnings.
We’re watching the process play out.
0 - https://www.defensenews.com/2020/12/21/the-military-is-scram...
The issue is that the FCC sale of frequency spectrum up to 3.98GHz doesn't have such limitations, so essentially in 2019 aviation got an unique problem of extra heavy interference in USA
“Fix the thing” is the correct answer, but managing risk in the meantime in this regulatory environment is a shade of grey. Doing nothing puts people at risk. Grounding aircraft cripples a critical industry. Delaying 5G costs two network operators a lot of cash.
You lost me here at this point in the comparison. How is this analogous to the situation with altimeters?
So even if the cattle stay within their limits, the grass relies on bees coming in from neighbouring farmland to stay healthy.
If you pave the area outside a cattle ranch the grass inside will die on the borders.
So you have to zone the land outside the fences to make sure it some other ranch or else left wild.
The same with spectrum. Adjacent frequency bands have to allocated to uses which do not produce a lot of interference that travels very far or is used very much.
If you're actually curious about this specific scenario, in the US it's typically referred to as "adverse possession": https://en.wikipedia.org/wiki/Adverse_possession
> in the English common law tradition, courts have long ruled that when someone occupies a piece of property without permission and the property's owner does not exercise their right to recover their property for a significant period of time, not only is the original owner prevented from exercising their right to exclude, but an entirely new title to the property "springs up" in the adverse possessor. In effect, the adverse possessor becomes the property's new owner.[2][b] Over time, legislatures have created statutes of limitations that specify the length of time that owners have to recover possession of their property from adverse possessors. In the United States, for example, these time limits vary widely between individual states, ranging from as low as three years to as long as 40 years.
Also, in some states like California you have to pay taxes on the land for a certain period of time before you can claim ownership.
But yes, in your specific case it is possible to raise cattle on someone else's land for long enough to be able to legally claim that land as your own.
A better analogy needs to understand that the filter on both sides of the equipment is imperfect.
Replace the altimeter with, say, Mount Rushmore National Monument, and replace the wheat farmer with, say, a putrid landfill, sewage processing operation, or CAFO chicken farm. Neither the monument nor the viewing areas extend beyond the surveyed boundaries of the monument. But part of the appeal is that it's a pleasant, quiet, natural place in the middle of a national forest: abutting it with something smelly, noisy, or ugly might be legal but would harm it even though it doesn't extend past the property markers.
Personally, I do think they need to upgrade and phase out the altimeters to be more tolerant against interference. But they're not necessarily broken, just too slow to adapt past the scope and capabilities of the tech available in 1967.
This is the problem with analogy.
Yes. In your example, the government may decide to temporarily allow the rancher to keep grazing his cattle until the rancher can reduce the size of his herd, because they don't want to force him to destroy good cattle, while requiring the rancher to pay the farmer for the use of his land and lost profit from the wheat he cannot grow.
The alternative would be to force the rancher to cull half of his herd, which would not only be wasteful, but also cause a national beef shortage, while the world so far survived without the extra wheat. So the government does the pragmatic thing, even though it shouldn't, according to the permits it issued. Probably wouldn't happen with beef vs. wheat, but I could see it happen with beef vs. corn-for-ethanol, because food safety trumps ethanol production.
The FCC might decide that existing aviation needs beat not-yet-established mobile phone needs. Whether the spectrum owners would actually be compensated fairly, or whether the government would the "you're getting screwed over because I like the rancher more, I've got the bigger guns, what'cha gonna do about it?", - that I don't know.
But from the article, it sounds very much like the FCC isn't doing much except having told the farmer to wait a few months before plowing the greenest grazing land to keep the peace, and the FAA is telling the rancher "your not-your-own grazing land is gone so your cows might starve, deal with it".
I have posted this a bunch of times https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
I have read this carefully, and run calcs myself, the issue they are raising is the phones on the plane. But even at full power, very unlikely, but read my other post on this for more details.
The real issue is that they want the telcos to pay them to swap out their radar but are asking for a large amount beyond what would be needed to do that.
they are asking for money, come on.
this is what is wrong with HN, you can downvote without talking, be standup. what are you arguing ?
Regardless of whether this makes sense, the hypothetical scenario you describe is called "adverse possession."[0]
Now, it may be that spectrum doesn't count as property (especially since the FCC's existence derives from the fiction that "the public owns the airwaves"). This situation makes something of a mockery of that FCC narrative, since no one believes these airplane radars will all be replaced at the drop of a hat, but nevertheless it would probably hold up in court as a matter of law.
I have no idea how the government could try to remedy this situation. Seems like admitting adverse possession with some sort of compensation and/or trade in spectrum might make sense.
Whether radar altimeters in their present form are fit for purpose or not I cannot answer as I have insufficient information to do so. However, I must point out that:
1. ALL radiocommunications have limitations in that they can suffer interference from other services even when those other services are operating correctly and according to license (i.e.: being in their correct allocated frequency bands and operating at their correct power levels, etc.).
2. The role of Spectrum Management falls to the FCC. It operates under the auspices of the ITU (International Telecommunications Union) to manage the spectrum through its international treaties and its job is to ensure that interference between services is kept to a minimum. In essence, the aim is to maximize spectrum usage whilst keeping interference to trivial levels (it should be noted however there's no such thing as 'no interference').
(International treaties are necessary as electromagnetic radiation doesn't honor a country's borders.)
3. The way this is achieved is complex but in essence transmitter frequencies, power levels and transmitter locations are optimized to provide optimal protection ratios to each service so they can operate efficiently.
4. If services are mobile, as with radar altimeters, one of the parameters used in optimizing protection from interference is lost. Signals from radar altimeters can interfere with other services and vice versa as they can get too close to one another (interference increases significantly when powerful transmitters are close to sensitive receivers).
5. How tightly services can be packed together depends on many factors but two principal matters stand out: the laws of physics and the state of the art of electronics design.
The major culprit in causing interference is a well known form of distortion whereby several radio signals can interfere with one another to produce multiple other freqenies that are harmonically related to the original frequencies. This interfere is called intermodulation distortion and it's one of the perennial scourges of radiocommunications: https://en.m.wikipedia.org/wiki/Intermodulation.
For example, a transmitter on f1 (service 1) and another say on f2 (servive 2) can produce other unwanted frequencies, f3, f4, f5, etc. that can interfere severely with unrelated services. Under some circumstances interference to the unrelated service can be so severe that it can be rendered useless (as mentioned, this can be very problematic when services are mobile as it's very difficult to take every contingency or location into account).
6. These matters become much more critical when the stakes are high - with emergency services, radar altimeters, etc. where lives can be at stake if things go wrong.
7. Critical communications services have always demanded very high protection ratios and have traditionally been given them by Spectrum Management agencies - the FCC, et al. The current argument is that the ubiquity of 5G threatens the high protection ratio previously afforded radar altimeters.
8. If I were in the aircraft industry and I was responsible for the reliability of safety devices such as radio altimeters then I'd want to be absolutely certain that any new radiocommunication service is not going to interfere with any of my critical services. Moreover, I would be overly concerned with the potential for mobile phone services to interfere with these safety services specifically because phone services are a never-ending moving target when it comes to location, density of phone traffic, etc., all of which have potential to cause interference.
9. Whether 5G has real potential to interfere with radar altimeters or any other aeronautical communications service can only be determined by proper independent engineering studies.
The fact that we have this dispute at this late juncture shows that something has seriously gone wrong in the planning phase.
(From my observations, it seems the mobile phone industry has had too much political power, especially so when it comes to buying spectrum - and it has lots of money to demand what it wants (and to date it's gotten the spectrum it wants). Whilst government eyes the millions to be made from the sale of spectrum, the trouble is that it's also the regulator of the spectrum hence it has a conflict of interest.
Fundamentally, spectrum auctions run by governments have the potential to compromise good spectrum management. Whether it's happened in this instance I cannot say for certain.
The only other point I'd stress is that the electromagnetic spectrum is a scarce nonrenewable environmental resource and should be respected and treated as such (like any other environmental issue).
It sees grass. It eats.
It seems like the telecom and aviation industries (along with the FCC and FAA) disagree on a question of fact: does 5G equipment interfere with radio altimeters?
There’s a way that the FAA could convince me, and probably all the politicians. Shoot a video with a radio altimeter and some 5G equipment where the radio altimeter malfunctions. Put it on YouTube. Do a press release.
This seems like an obvious step if the underlying issue exists. Any reason they haven’t done this?
Which is a harder question to answer, but how seriously we should (and usually do) take air safety.
The way you test this stuff is get a rad-alt and inject known amounts of RF and see how much is needed to give false readings. Then you go and measure how much RF you'll see in the environment and see if it exceeds those levels.
Here's a choice quote from the summary: "In the worst case, the safe interference limit for the fundamental emissions is exceeded by over 47 dB, and the safe interference limit for the spurious emissions is exceeded by over 27 dB."
Speaking a bit from my own experience, I suspect the guard bands on most radalts out there are wide enough that 5G interference isn't a practical issue. I've seen radalts with 30 MHz guard bands around the 4.1 GHz / 4.3 GHz limit frequencies of interest... and that's friggin' huge. (I'm also sure there are radalts with much smaller guard bands that use more of the available bandwidth for better performance.) But this is hard to analyze fully. Taking the example of the unit I'm thinking of, the center frequency is from a non-temperature-compensated oscillator -- so your worst case is an extreme temperature going to assymetric guard bands, a unit with a weak bandpass to begin with, and a 5G system pouring a lot of energy at (or even, in violation of spec, a bit beyond) the edge frequency. Probably fine. 10^8 fine?
Annecdata, but... I know two commercial pilots who have both recently run into interference with their radar altimeters during landing/takeoff. It certainly doesn't affect all aircraft (depends on the particular avionics installed), but from what I've heard it is a real issue.
The problem is that radio altimeters are pretty old, and their filtering technology is not great. So even though they are filtering the 3.7-3.98 GHz 5G band, it's not as effective as a modern RF system/filter would be. Previously, this wasn't the issue because nothing was broadcasting in that band at particularly high power.
That's the second component of the problem: power. The radio altimeter system is capable of handling some amount of noise power caused by unwanted broadcasts, among other things. Previously, satellites were using this band, and they were so far away that between the distance-based attenuation of the signal and the limited filtering, radio altimeters could operate unaffected.
5G is a different story, though. The towers are much closer to the runway, so the leakage power is much higher. Whether this actually causes a problem for the altimeters is then dependent on a number of factors, including the distance to the 5G tower, the transmit power level, the direction of the 5G antennas, etc.
Could it cause a problem? Sure. I bet if you pointed a directional 5G antenna straight at a particularly crappy radio altimeter, you could materially affect its operation. But there are many mitigation strategies that could be used, like requiring lower transmit power, further antenna distances, appropriate directional transmissions, etc. These strategies have been used successfully in other countries.
The real concern should be the total lack of collaboration between the FAA and FCC. It's turning into a jurisdictional pissing contest.
Interestingly the 737-200 is excluded from this airworthiness directive. 737-200s are the oldest, still-operating members of the 737 family.
The entire aviation community has been aware of this issue and the manufacturers have been working on it.
It's not an exaggeration to say these things take time. "Move fast and break things" doesn't work well with aircraft.
Sure, but that didn’t seem to stop faulty lithium batteries on the 787 or MCAS on the 737-MAX. If only Boeing would learn the lesson, maybe we wouldn’t have these messes.
If anything, Boeing has been very proactive about identifying the affected equipment well before any accidents happen. This is precisely what they should be doing.
1) I never stated the radar issue was only Boeing’s “problem” previously, I stated it’s yet another example of a mess they are in which ultimately boils back to a “move fast and break things” attitude being a major cause (just in this case, it was more the FCC to blame for that attitude)
2) It ultimately is their problem to solve for the airframes they sold however, whether it was their fault or not.
> If anything, Boeing has been very proactive about identifying the affected equipment well before any accidents happen. This is precisely what they should be doing.
Link to the ADs from Boeing saying which models are susceptible? I hadn’t seen that
AD 2022-03-05: https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf...
AD 2022-03-20: https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf...
AD 2022-04-05: https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgad.nsf...
As part of trying to keep flying safe, both attempts to limit sources of interference (i.e. 5G transmitters) and checks on existing hardware (and thus whether it needs to be replaced) are done in parallel. Outside of USA, everyone agreed on various mitigations to limit impact to radar altimeters especially as full impact of C-band 5G is still work in progress.
The lower frequencies used by Europe for 5G are already allocated for amateur and other uses here in the US. I believe Europe has been more willing to take away amateur bands.
However here in the US, the FCC was trying to maintain those existing allocations and thus they chose to reuse 3.7-3.98 GHz instead, which is currently allocated for fixed satellite and other links.
Therefore what FCC did is potentially better for everyone, if we can find out that radio altimeters—which should be filtering out frequencies that never belonged to them—are still able to work correctly.
The issue is that, as you may know, if you engineer for something but don’t actually regularly test for it, you never actually engineered for that case. Up until this point, this case was never tested in production… because it has never existed in production.
At the end of the day, we are between a rock and a hard place.
and actually not only are they old but they are defective - they were designed to function with guard bands half the size that the FCC ended up giving them, and they still are running into interference. They are basically picking up way way way more than they were originally specced to, and that's suddenly a problem because somebody moved in next door.
also to my understanding it's specifically a problem with Boeing and other aircraft are much less affected. So we are also running into the "boeing has become a quasi-state enterprise that is too-big-to-fail and will be protected under all circumstances even when they do something obviously dangerous", like the MCAS system on the 737 MAX.
honestly I kind of feel like the real situation here is that Boeing needs to issue an airworthiness directive and have those altimeters replaced. If a wing broke at half the loading spec, we wouldn't hesitate to say that's faulty and should be replaced. But with guard bands twice as wide as initially specced these altimeters are still having problems? Get them out of the air until Boeing fixes them.
> The real concern should be the total lack of collaboration between the FAA and FCC. It's turning into a jurisdictional pissing contest.
they were collaborating a long time ago - but again, there is only so much you can do when it suddenly turns out that a 2x margin of safety from the design spec (which itself incorporated a margin of safety) is not nearly enough.
the spectrum was sold a long time ago. the airworthiness certificates were issued decades ago. At this point there is no solution possible that doesn't make somebody unhappy.
I lean towards the party that needs to be made unhappy being Boeing here - but that will make airlines very unhappy as well. Saying "no you can't use that spectrum" is an unconstitutional taking at this point, you auctioned it off for cash monies and that absolutely puts a legally enforceable price tag as a minimum bound - in practice the value is higher since business plans have been built on it. But there is no constitutional right to fly a defective aircraft, if the FAA grounds your plane because it's unsafe that's not a taking.
But that will have a massive impact on boeing, airlines, and the economy as a whole.
Take the recent 737 MAX debacle as an example. Its MCAS hadn't been proven to be dangerous when it went into production, but it turned out that it was. Result: two airplanes fell out of the sky and 346 people died. It's the FAA's job to prevent this sort of thing from happening, and in this case (unlike the 737 case) they're doing that job.
Truly, it's amazing how many aerospace engineers hang out on HackerNews!\s So many assertions about what is right, what is wrong, and who is to blame. 99% of these assertions reflect a poor understanding of how commercial aviation fundamentally and functionally works.
Not only is your comment 100% correct, it also strikes at the heart of the problem. Diplomatically, the issue that exists today is a clash of the very different safety cultures that exist between aviation and telco (and by extension the FAA and the FCC.) Aviation will win, btw. The question, however, is at whose expense.
Btw, the root of all this can be traced back work the aviation industry had undertaken to create a standard for wireless safety critical avionics (a system and standard called WAIC.) It was about four years ago that the aviation industry tried to secure additional spectrum, was denied, and thus started researching how to use the existing 4.2-4.4ghz spectrum already dedicated to aviation. It was through this research that the industry discovered the inherent problems with radio altimeters and nearby spectrum interference.
The aviation industry petitioned the FCC during the notice of comment period for the C-band spectrum sale, sharing the research and the data which shows 5G interference could be a problem given how it was planned to be deployed in the US. T-Mobile did their own preliminary study in support of the aviation industry's findings, but the rest of the telco industry attacked the research done without providing their own alternative data. The FCC, under Ajit Pai, and with support of the telco's lobbying arm CTIA, then effectively politicized any additional technical assessment or study, leading to today's brouhaha. If you want to blame anyone, blame the FCC and their former chair, who btw, is already a favorite internet punching bag.
(Note that T-Mobile is the only carrier that did not purchase the spectrum, although it's not known whether this was due to T-Mobile's own supporting research.)
which i have posted a bunch of times.
I am 40+ year experience in this area, I have run the calcs, the thing they are worried about is the phones on the plane, the phone would have to be less than 2 meters from the radar antenna and at full power to come even remotely close to the interference numbers they are talking about to give a false reading, and that would be without a lot of body loss.
The airlines want the telcos to pay them to swap out their old radar units, it is about money of course.
But I am not wrong..
the airlines are asking for money.
However, it doesn't surprise me that the FAA, which allowed the Boeing 737Max fiasco, is back here coming to Boeing's defense. What happens when 2 captured regulators collide?
Edit: added spacing and changed "radio" to "radar" for clarity
[0] https://www.npr.org/2019/07/02/737919100/forecasters-caution...
When moneyed interests compete it becomes the same as their being no moneyed interests
An average case outcome
Not obvious what would happen here though, just a general reality that mostly undermines the “rich shadow organization controlling everything” idea
No. That's very incorrect.
For example: Moneyed Interest #1 wants A & B, Moneyed Interest #2 wants A & Not-B. It's entirely possible that Not-A is a bad business model, but is also in the interest of the citizenry at large to have Not-A be law.
You are describing the 23.8GHz radar used by satellites.
The FCC is more political than the FAA, but the FAA more critical to US economy. As of right now it seems the FAA is winning.
The FAA serves Boeing -- and no one else right now.
Downfall says “the crew knew about the MCAS risk, figured out they had an MCAS fault, applied Boeing’s checklist response, and still the airplane crashed”. All four of those things are independent and true facts.
What is omitted (and readily available to the filmmakers) is that EA302’s thrust setting remained inappropriately high (94% N1, takeoff thrust), causing an excessive airspeed, causing the crew to be unable to return the stabilizer to a normal trim setting by hand after using the electric cutout, which led them to the (correct) conclusion that they should turn the electric stab trim back on and command aircraft-nose-up via the electric system, which they did. That means that they undid the checklist response. Then, after doing that successfully for a short period of time, they stopped commanding nose-up trim and left the stab trim powered up (contravening the checklist), allowing MCAS to continue to command the fatal nose down trim.
So they got dealt an emergency situation and the airplane crashed. Boeing has some blame here, but Downfall’s presentation of the events as the crew responding correctly with Boeing’s checklist would make most politicians blush and worry they’d be caught lying.
You could say Gravity contributed I guess to both crashes, and Boeing is not responsible for that, but the difference here is that Boeing deliberately hid the existence of MCAS to the pilots to avoid simulator training.
Further the FAA is extremely dependent on the FCC, being unable to detect or communicate with aircraft would make air traffic control nearly impossible. They would still be responsible for crash investigations, pilots, aircraft manufacturing etc, but in the worst cast the only way to fly safely would be under clear skies.
This is because the FAA is under the United States Department of Transportation, while the FCC is an independent agency. https://en.wikipedia.org/wiki/United_States_Department_of_Tr...
To see the difference goto: https://www.usa.gov/branches-of-government
Executive Department Sub-Agencies and Bureaus has FAA. Independent Agencies has FCC. What is and isn’t an independent agency is complicated but the EPA, NASA, FDIC, Federal Reserve System are independent as are less critical agencies like Institute of Museum and Library Services, Peace Corps, and Railroad Retirement Board.
I think that's the NTSB? Otherwise you're not wrong about air traffic control, equipment and pilot certification.
https://pilot-protection-services.aopa.org/news/2020/july/01...
The dual role is more clear when you consider investigations may uncover issues that are irrelevant for this crash but could cause other crashes.
Now, I do agree that this should have been caught 5-10 years ago, when the standard was being developed. Boeing's incompetence wouldn't surprise me, which is probably why we see "FAA says problems for Boeing in 5G" as the headline, instead of "Aircraft companies warn of interference in safety, navigation equipment, ask FCC to reconsider" as the headline, 5 years ago. Although, as noted in the article, it seems that the FAA has been warning about the conflict - I'm just surprised that the FCC would go ahead with 5G if they had been flagged early enough.
So here we are, the FCC, in its negligence, assigned conflicting portions of the spectrum, Boeing, in its incompetence, didn't catch it - and now it's a big mess.
They mostly did. They've been warning about this for 3+ years now (see this report from the FCC back in September and October 2019) https://ecfsapi.fcc.gov/file/102214765103/AVSI%20RA%20Interi...
They couldn't have warned folks about more than a year or so sooner than that, because the spectrum bands for 5G hadn't even been fully decided prior to it. (The public notice of band reconfiguration only got announced back in May 2019)
This statement seems to be at odds with what many others in this thread are saying: that they were never approved to operate in this band. I don't know enough about this issue to know who is correct--do you happen to have a source for that since you are certain of it?
Why? They don't make the radar altimeters and multiple aircraft manufacturers are affected. Why is Boeing at fault for issues that (also) manifest themselves on Embraer and Airbus aircraft?
No they don’t, and never have. Hence the current shit show today.
Boeing got away with it because old users of the 5G spectrum where lower power satellite comms. Hilariously the oldest 737 model is unaffected by this issue, probably because Boeing actually let their engineers do good work back then, rather than forcing them to produce the sloppy crap they build today in the name of profit.
FCC has allocated radalt's 200Mhz, with another 200Mhz guard on either side. If these devices are not properly filtering out frequencies outside of this massive 600Mhz range, those devices are faulty and should never have been certified by the FAA in the first place.
It's reasonable for the FCC to assume that spectrum users will not be affected by interference from so far outside their allocation.
It seems there a disagreement on factual truth which as another commenter pointed out could be resolved by say a YouTube video showing "here's a radar altimeter malfunctioning near a 5G antennae"
Also your comment seems inconsistent with the fact that the telcos delayed deployment of 5G towers near airports due to concerns about interference during takeoff and landing. So how can there be reports of interference from 5G tower if they haven't even been deployed there (edit: are these international reports)?
(I work on radar, this all feels like lawyers lawyering and techies blogging, but not engineers engineering)
I don't know of any commercial pilot who is going to jeopardize their job and their certificate by filming a YouTube video while landing. There is literally no incentive for them to do so - there's formal channels to report these things (like ASAP, see above).
Also, while turning on the 5G towers near airports was temporarily delayed, it was only a short delay (two weeks). Those towers have already been turned on.
https://www.bloombergquint.com/amp/business/pilots-report-ov...
“The reports have come in the form of radioed descriptions to air-traffic controllers as well as through more formal incident-reporting channels. The FAA often gathers unconfirmed reports of aviation incidents, such as drone sightings, even if they’re difficult to verify. At least some of the reports from pilots of possible interference have occurred at locations where the C-band broadcasts don’t exist, suggesting no connection with the service, said two people briefed on the issue.”
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.
What is your basis for this extraordinary claim?
Depending on the strength of 5G transmitters the higher order harmonics could be above the noise floor.
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.
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.
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.
“Immunity” is largely your own problem though.
That's specifically for unlicensed Part 15 devices ref. 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.
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.
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.
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.
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.
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.
Please link to this specification. Because I've read the specification (TSO-C87), and it actually says nothing about required levels of interference rejection.
Should it? Probably. But neither the FCC nor the FAA wrote it in.
Any leaking that happens is caused by the 5G transmitters in the case under consideration. You are confusing two issues. The issue here is that strong and close transmitters can not be properly blocked by some of the radar altimeters in use under the separation rules established by the FCC.
An important job of the FCC is separating TV transmitters that are close in frequency so that they do not cause problems. If you live next door to a TV transmitter you will have no hope of receiving signals on adjacent channels. That is because of the physical limitation of your receiver and has nothing to do with the transmitter leaking anything.
Is there spectrum assigned alongside the radalt to ensure no crosstalk?
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)
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)
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.
[0] https://strandconsult.dk/blog/5g-is-suddenly-a-flight-safety...
Why the US decided to use 3.8 GHz for their 5G, only God knows.
200Mhz is an eternity away. You can fit all of the 2.4GHz WiFi/Bluetooth/whatever unlicensed band in that.
The radio altimeters are fully up to spec, but the spec does not say enough about filtering out signals outside of the required band. This oversight in the spec was never much of an issue because of the aforementioned lack of usage in the spectrum before 5G.
US 5G uses 3.7 to 3.98 GHz
Blancolirio covers this in several videos, although his take is more nuanced than mine.
These radar altimeters have very wide front-ends, as as a result are highly susceptible to out-of-band emissions. The radars are allocated from 4.2 to 4.4 GHz, so the bottom edge of the radar altimeter band is 200 MHz above the top end of the 5G band in question (3.98 GHz).
The fact that these radar altimeters are susceptible to out-of-band interference that is literally further away in the spectrum than the width of their entire allocation is IMO an engineering failure. Yes, spectrum management (rightfully) tends to err on the side of not forcing the incumbents to make modifications to existing systems. However, better filtering would resolve this issue and it is shocking that the engineers who designed them didn't foresee that other services would eventually be allocated in adjacent bands. Avionics is often NRE dominated, they couldn't have sprung for a cavity filter? Or if that was too expensive, designed more headroom in the LNA before saturation and filtered the out of band signal with a crystal or SAW filter at IF? Rejecting out of band that far away is not rocket science.
I don't think it's unreasonable in this case to temporarily suspend the rollout and give the aviation industry a deadline to fix its radars, but it should only be temporary. Any other radio service would be told to take a hike if it keeled over due to out of band interference that far away.
I completely agree that Boeing needs to issue a recall order on all affected hardware and provide a fix. This should be painful, it is basically punishment for trying to cut corners on safety equipment.
An modern commercial plane has tens of thousands of suppliers supplying millions of parts. No airline [1] could even imagine to have the staff to manage OEM relationships with that many indirect suppliers. That is what you pay Boeing for.
If that was the case no airline could afford to buy more than 1 type of plane or certainly not more than one manufacturer, you would need to handle all the suppliers in the industry?! it would be incredibly inefficient to do this for them individually .
---
[1] Maybe United , American or Delta could have that kind of staff, but given the airlines operating margins in the last 2-3 decades even that seems unlikely
And you're grossly overstating how many suppliers are on a commercial aircraft. There are in total an average of 30 tier-1s on a modern airframe, and yes, airlines are expected to work with all of them. Radio Altimeters are typically made by avionics suppliers i.e. Collins, Thales, or Honeywell for Part-25 commercial airliners.
There's a reason why the only time two airplanes are identical is when they roll from assembly line as part of the very same order with same spec, and never again.
Boeing can argue with and sue their suppliers, but that's not a problem for anyone but them and their supplier.
If I made routers that flood the EM spectrum with random crap, even if their wifi 'worked' they wouldn't be fit for use, either.
Second, the FCC was already involved in their development and certification.
Third, these radars have been in operation for decades.
You are talking about thousands of planes that have to be modified to accommodate telcos. If anyone should pick up the tab for this it is Verizon and AT&T.
That makes their domination of spectrum far outside their range worse.
If anything, threaten to retroactively charge them for all that bandwidth.
Perhaps Boeing should have bid of the spectrum that their products depend on being unused.
This is essentially the government leasing out previously unused federal land for mineral extraction and a nearby rancher saying "it ruins my view," only with safety concerns added in.
This spectrum can’t simultaneously be “unused” and a problem for radar altimeters.
Who cares? The comment you are responding to says "they did shoddy work on the altimeters." That doesn't mean that Boeing built the altimeters.
They specced them, procured, inspected, installed and sold it with the whole airplane. If the pilots' chair collapses, that's shoddy work on part of Boeing, and nobody would talk about how they are just buying the chairs from someone. Same with the radio altimeters.
> Third, these radars have been in operation for decades.
Ok? Sometimes corners cut bite you in the backside only after decades.
There is one question which matters: Are the 5G towers transmitting on frequencies assigned to the use of radio altimeters or not? If they are they must stop. If the radio altimeters degrade or might degrade because of transmission outside of their assigned range and guard then they are faulty.
I believe no agency should consider downstream effects of applying the law, to ensure fairness. Why should Boeing get a pass but say an out of compliance robotic lawnmower gets enforced?
(I do agree this is Boeing's issue to fix, 200MHz guard band is huge, Boeing needs filters)
The allocation of the spectrum is only for transmission, and the radar altimeters in question passed that spec. It says nothing about receive, and due to how radar altimeter works, it's much, much harder to filter out interfering signals from systems like 5G (5G in case of interference will just drop maximum data rate as it filters mismatched codes or incorrect checksums, radar altimeter might return incorrect altitude)
I think one of the big things in the US is that anything that makes C-Band harder to work with makes it hard for 2 of the 3 wireless carriers to compete. T-Mobile has a lot of 2.5GHz spectrum that it has been using to launch high-speed 5G services. Verizon and AT&T had been waiting for their C-Band spectrum to be usable to launch their high-speed 5G services. In Europe, if all carriers are facing the same restrictions, it's a level playing field. In the US, if Verizon and AT&T face restrictions that T-Mobile doesn't face (for most of its spectrum since it's 2.5GHz and not C-Band), that doesn't offer a level playing field.
I think it's also more contentious in the US because we have a much more suburban and rural population. Transmission distance is really important in the US because people expect to get modern services even in low-density areas. Verizon built its business on the idea that you should expect excellent wireless coverage even in places that have virtually no people.
I think another part of it is that the FAA is often very cautious and it seems like they didn't coordinate well with the FCC in voicing their concerns early on enough.
The FAA does have a web page on C-Band (https://www.faa.gov/5g) which is their official stance on the subject. They cite "Lower power levels, antennas adjusted to reduce potential interference to flights, different placement of antennas relative to airfields , and frequencies with a different proximity to frequencies used by aviation equipment" as reasons why the C-Band situation in the US is different from that in other countries. Is the FAA being too cautious? Maybe.
Ultimately, no one wants their business plans disrupted. Airlines don't want to see issues that delay landings. Verizon and AT&T don't want to see things that delay their ability to provide fast 5G service.
(I mean that i do not know the answer)
do remember we're talking about commercial aircraft where software updates are still deployed on 3.5" floppies.
it's difficult because obviously this is not a domain where "move fast and break things" is an option, I certainly see the benefits of a conservative engineering culture. But the 737 MAX situation already happened as a clever end-run around not being able to touch anything, and not being able to touch anything is more broadly killing general aviation (small aircraft). Extremely few aircraft have been certified since the 80s when the new regulations went into effect, it is very expensive and difficult. And at some point that boils down to encouraging "the wrong fix" or simply ignoring problems.
these aircraft have defective radar altimeters, they are unable to function properly with a guard band over twice the size of the original design spec. The other problem here is regulatory capture - these aircraft shouldn't be in the air at all with a radar altimeter that is so dangerously defective. The right fix isn't "just let aircraft manufacturers ignore certification requirements when it's convenient", it's to come up with a level of certification that promotes a culture of engineering safety, but basically the FAA is just letting boeing keep dangerous planes in the air because it would be a mess if they didn't.
A radio altimeter is not required equipment for flight, nor does lack thereof make for a dangerous aircraft.
It is required for certain approaches used during periods of poor visibility. The FAA has correctly published NOTAMs and ADs prohibiting those approaches.
There is no need to ground aircraft over this.
In this episode, AIN contributing editor Mark Huber explains the 5G C-band interference issue that can affect aircraft radar altimeters. He explains how we even got into this situation, why there is the potential for the 5G wireless networks at Verizon and AT&T to interfere with radar altimeters, what the FAA is currently doing to temporarily ease the problem, and what can be done long term to solve this issue.
Here's the actual text, so it's only some of the 200's that are unaffected:
"Based on Boeing’s data, the FAA identified an additional hazard presented by 5G C-Band interference on The Boeing Company Model 737-100, -200, -200C, -300, -400, -500, -600, -700, -700C, -800, -900, and -900ER series airplanes, except for Model 737-200 and -200C series airplanes equipped with an SP-77 flight control system"
And the SP-77 does include a radio altimeter...apparently a nicely selective one.
https://public-inspection.federalregister.gov/2022-03967.pdf
https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
which is the complete report you can read for yourself that the FAA based their "concerns" on.
But, if you read between the lines, or at least my read on it is... The wireless telcos agreed to pay the Incumbent Earth station operators to vacate the spectrum, the Airlines are a little cash strapped after the pandemic lock down, so, they figured why not stick our hand out and see if we can get a little cash out of the telcos.
Just my take on it, but reading the RTCA doc, the whole thing is completely baseless.
But, having said that, here is something to consider, the primary concern raised by the RTCA is not so much the base stations themselves, which are far away and hence, not an interference source, it is the phones on the plane as it lands, which are much closer to the radar antenna which is in the ass end of the plane (the lowest point on take off and landing).
If a phone is on in the plane it will drag the call along, if you turn down the BTS's around the airport this compounds the problem because the dynamic power control of the phone will power up in an attempt to hold the connection. In Europe, they have been using this same spectrum for a long time with no problems, so in the U.S. we are doing the opposite and turning down BTS's near airports. So do the opposite of what works elsewhere in response that actually aggravates the exact problem being raised.
In other words, the best thing is to leave BTS's up near the airport so the phones, closer to the radar antenna, will not interfere, like what works in Europe, so the phones don't increase power. So, we are doing the opposite.
Several months ago when the grumbling got loud, all the articles seemed to talk about "potential" interference, and despite the FAA having an $18 billion annual budget, and Boeing and Airbus and airlines having bigger budgets than that, and having almost 5 years notice, I got the distinct impression that no one had bothered to do any tests. But they took to the media to raise the alarm about "danger" instead.
I'm actually hoping to be proven wrong here - please point me to some experiments or test results!
"The extent of the RF interference is summarized by the worst-case exceedance of the safe interference limit of radar altimeters by expected 5G signals in the 3.7–3.98 GHz band: 14 dB for commercial transport airplanes, 48 dB for business, regional, and general aviation airplanes, and 45 dB for helicopters. Further, the impacts are not only limited to the intentional emissions from 5G systems in the 3.7–3.98 GHz band, but also the spurious emissions from such systems within the protected 4.2–4.4 GHz radar altimeter band directly. In this latter case, the worst-case exceedance of the safe interference limit is 28 dB for business, regional, and general aviation airplanes, and 12 dB for helicopters."
https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
but really, it's the phones on the plane that are the problem, because they are closer.
https://www.rtca.org/wp-content/uploads/2020/10/SC-239-5G-In...
https://www.wsj.com/articles/pete-buttigiegs-5g-crash-landin...
Overall it seems like the FCC was trying to be innovative, while the FAA's precaution in fact is the malaise that's been infecting all of US government: overapplication of the precautionary principle, that any risk, even if small an theoretical, is worth stopping change for (but not asymmetrically for motivating change).
Being wholly inaccurate or no reading may be equally dangerous if it happens at the wrong time.
Amazing they can't do GPS as a cross check on indicated altitude over a terrain model.
I mean they could, but they skimped out on just getting a halfway decent filter for frequencies 200MHz away from their signals what are the odds they'd pay for that.
GPS altitude is used for LPV approaches, provided you also have a WAAS correction signal, but those require higher weather minimums than the Cat II/III approaches that you'd use a radio altimeter for.
2. Boeing doesn't get to decide to just cross check against GPS. The FAA has rules about the equipment that can be used for various types of landings.
The problem is that radar altimeter is very precise device that for best precision needs to use all of its 200MHz bandwidth on transmit. And there are no methods to recognize that as part of the return in its own 200MHz band (or in the guard band) a random CDMA-encoded signal radiated outside of allocated spectrum (happens) reflected of random crap around the airport and gets interpreted as valid data. This is an analog system where the analog characteristics are core to how it works, so the methods that allow tight channel spacing in communications tech do not work for radar altimeters
So "this altimeter may be inaccurate near 5G" means "this airliner may not be airworthy near 5G" which means airlines must ground those planes. It sounds like there are enough of them that it'd seriously affect air travel.
Recommend https://youtu.be/I9QHvd2bOvU which even managed to work some 5G-related jokes in there.
No, they don't need to ground the planes.
There's different types of IFR approaches available to chose from, depending on equipment and how much visibility is reported. An inoperative radio altimeter means the aircraft couldn't land using the approaches for the lowest-visibility conditions, but doesn't mean they can't land under other less-severe IFR conditions.
In practice, this means the aircraft wouldn't even be dispatched if the weather forecast showed the destination's weather was below the aircraft's capabilities. They would also have enough fuel to divert to an alternate airport with better weather.
This was a horrible decision, because those fees are, in effect, a tax, that will inevitably be passed on to the users.
On top of that, it provided the incentive to take what was a reasonable separation that protected aircraft navigation bands from other users, and sell that space off.
On top of that, the FCC/FAA didn't bother letting the rest of the world know this was going to happen, even though they had YEARS to do so.
Thus, the current mess. Signals are popping up where the equipment currently in use was never expected to tolerate them. It's putting lives in danger.
On the other hand, maybe it makes more sense for insurance carriers to simply refuse to assume liability for flights on airplanes with altimeters that are known to have issues with 5G tech. That approach seems to work for discouraging new construction in floodplains.
You save more lives by having an engineer analyze potential problems with the plane before it crashes, than you do by waiting for one to crash so an actuary can count it.
Let's also not forget 5G equipment will emit outside of its assigned spectrum even with a buffer zone between frequencies. Especially when you consider the harmonics. Now each order of harmonic gets weaker from primary frequency.
As for these altimeter sensors anyone have a datasheet for them? Quite curious what the recommended noise floor for these are?
FAA is really the problem not Boeing, like any company they only did the bare minimum required to get certification .
Had FAA they mandated stronger specs initially or at-least forced Boeing to upgrade in the last 10 years this was being discussed and allocated, this won't be a problem. That will be expensive for Airlines(grounding loss of revenue) and Boeing (recall,certification and upgrade) nobody wants to foot the bill so FAA kept delaying .
Time and again we have seen FAA favor the industry even at the cost of lives (like with 737-MAX grounding) so this is not all that surprising from them
Also you can't make a perfect band pass filter, also for radar the band your going to be filtering is gonna be wider to begin with. Also all transmitters will emit higher order harmonics of the primary frequency, if the broadcast power is high enough those harmonics could very well be above the noise floor of other frequencies.
The FAA is only calling out 737s after clearing them in this statement . They had said on 20th Jan "Airplane models with one of the 13 cleared altimeters including all Boeing 717, 737, 747, 757, 767, 777, 787, MD-10/-11; all Airbus A300, A310, A319, A320, A330, A340, A350 and A380 models" [1] and now backtracking
They had adequate time to plan and roll it out to affected planes and they have not for the same reason telecom and FTC are upset -- money . Airlines/Boeing/ FAA do not want to foot the bill of this upgrade. Telecom companies spent $70 Billion on the spectrum and delays are costing them so they are upset.
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[1] Jan 20, 2022: https://www.faa.gov/newsroom/faa-statements-5g
FAA on Jan 20th of this year made a statement saying all these planes were approved to use under current new conditions for 5G. Now have since rolled back that for 747s(on Jan 25th) and 737s(23 Feb/27th Jan). Read their statements linked carefully again.
It tells FAA is not competently handling the situation. First they are caught totally unprepared for the 5G rollout after having years of notice, then issue approvals and are rolling back said approvals. At this point I am not inclined to believe they know what they are talking about at all.
In fact, apparently issues started cropping up with 400MHz guard band used in most of europe, when the towers malfunction.
It just happens that Boeing finished checking out a bunch of configurations that they have sold in the past against interference from 5G under FCC allocation (AFAIK they previously checked against setups allowed in other countries), and published results.
Airbus and others are also performing extra tests now.
This issue hits ALL PLANES that use standard frequency radar altimeters. Including Airbus, Bombardier, Cessna, Learjet, Dassault, etc.
What happened is that aside from trying to put limits on transmission characteristics for C-band near airports, there is a concerted action to verify how the many different models of radar altimeters interact with 5G interference. This is a report on configurations sold by Boeing, from Boeing, as they went over all configurations they've sold of specific types.
To extend the resource list, this (https://5gamericas.org/wp-content/uploads/2021/07/Mid-Band-S...) is a comprehensive analysis.
Millimeter-wave spectrum (in the 20-50GHz range) has lots of spectrum available, but its range is often in the 50-300 foot range. It's also important to realize that because we're talking about a radius, when we turn that into a circle the difference gets magnified. A 1 mile range means covering 88M square feet. A 100 foot range means covering 31,000 square feet. 53x more range turns into 2,800x more area covered.
Initial 5G networks in the US often used 5-20MHz of low-band spectrum (below 1GHz). This does have some utility as 5G NR is marginally more efficient, even in low-band spectrum. However, deploying with 100-200MHz of mid-band spectrum offers the kind of huge gains that offer 10x (or even more) data speeds.
https://assets.weforum.org/editor/SPPQ747R8Fd63ilAo4xvfjMNFU...
There isn't really a lot of spectrum that hasn't been allocated so it's often a game of figuring out who you can move for the least cost and most benefit. They chose to move C-Band satellite operators (at a cost of billions). Previously, the FCC freed up spectrum in the 600MHz range by having TV broadcasters relocate from UHF channels above 37 to lower channels.
Is there not any room in the regulatory world for “better safe than sorry”? At some point we could maybe just stop adding new energy waves to the sky.
It’s like the Wi-Fi router thing, it’s to the point where I’m going to need to buy a big piece of land to live on just so I don’t have 50 different Wi-Fi networks bombarding my house 24/7. I mean they say it’s safe to have a Wi-Fi router but did they study having 50 at once?
Ever tried to use 4G in a crowded place? Network congestion is the main reason.
Because it consists of non-ionizing EM waves, the risks of which are very well understood.
https://www.youtube.com/watch?v=i4pxw4tYeCU
And if you're concerned about the amount of non-ionizing EM waves in your environment from these 50 wi-fi networks, you should never go outside, since the sun is constantly blasting you with ~1,000,0000 GHZ-frequency electromagnetic waves, at an energy flux of ~1300 watts/square meter. It's half a dozen orders of magnitude more[1] energy than those fifty wi-fi networks are putting out. They aren't even a rounding error.
The only thing the 5G 'controversy' reveals is that the public is happy to listen to people who don't know anything, as long as they are being told what they want to hear.
[1] Not just more energy, more dangerous energy. Solar radiation, unlike 5G, is actually ionizing. Those radiation waves carry enough energy to break molecular bonds in your body.
"A case series of 64 patient-reported outcomes subsequent to use of a silver-threaded cap designed to protect the brain and brain stem from microwave Electrosmog resulted in 90 % reporting “definite” or “strong” changes in their disease symptoms."
(edit: in case it isn't clear, this is not how you science)
As these patients were all ill, many undergoing olmesartan treatment with therapeutic intent, we decided that ethical considerations precluded the distribution of “placebo caps” without the silver threads.
And they were apparently distributed to those that requested them, likely those that already thought they would work:
Sleeping caps” were sewn and, upon informed request, distributed free of charge to members of our follow-up olmesartan cohort.
Humans have a barrier, known as the “skin”, that’s designed to block the electromagnetic radiation from the sun and repair the damage it causes. Many of us even have an extra protective compound in us known as “melanin”. Nevertheless, damage to this barrier from the sun is responsible for causing many cases of cancer and people often wear protective compounds, known as “sunscreen”, to reduce cancer risks by blocking out the most dangerous ionizing radiation.
Wifi signal drops off with the square of your distance from the radio. So if you feel safe sitting 5 feet from your own router, you're only getting 1/25th as much signal from your neighbor's router 25 feet away (well, almost certainly less since it's going through walls, windows, etc). (some factors can change this, like if he has a high gain directional antenna pointed directly at you, you could see more power from his router than from your own)
So unless you're sitting in a Wifi router store surrounded by wifi routers, you're not getting irradiated by 50X more power even if your computer can see 50 wifi networks around you.
Because smartphone sales have leveled off and consumers are content holding onto their devices longer.
Manufacturers and telcos have become addicted to the 1-2 year device renewal cycle and want it back. Thus the marketing department instills “5G” as a need in the mind of the consumer.
Also, for people on metered plans, it behooves the telco to develop means for you to exhaust your quota as quickly as possible to get you into overages (and subsequently onto a pricey unlimited plan).
Everyone complains about the lack of choice and competition and quality among internet service providers (ISPs.) 5G is fast enough that you can use it to replace your wired internet, just as cell phones displaced "land lines" over the past two decades. 5G, and hopefully Starlink, will be ISP game changers.
The airlines have basically claimed squatters rights to those frequencies owned by 5G carriers.
The MAX safety record is terrible because there are many incidents per flight hour. Not because there are many incidents.
It needs to fly about 10M flights per fatal accident to be catching up with the 737 NG.
That said the 737 MAX fuckup is something that neither Boeing, or the many worldwide air travel regulatory institutions should be forgiven for. But that doesn't make the 737 design itself bad. That particular iteration, due to Boeing's attempt undertake Airbus and falsely sell the planes to airlines as a drop in replacement with zero extra training needed unfortunately resulted in deadly crashes. The people that decided on that should be charged on the deaths that occured because of their greediness.
For whom should the buck stop? Boeing, who designed the upgrade with lower carrier costs in mind? The carriers who bought and flew a compromised flight program in order to offer lower ticket costs? The passengers who choose a carrier based on cost instead of quality?
Whoever decided on that should be mainly responsable for this. Of course the passengers don't have the fault and the airline would be at fault only if they continued using the decommissioned planes that were known to be unsafe. I'm not mistaken issues have been mitigates and those planes are in use in many areas of the world now.
There's nothing wrong with designing an upgrade with lower carrier costs in mind, but any potencial differences on how the plane behaves should always be informed, even if a computer is supposed to correct for it.
Hard to blame them though - while it was definitely pilot error when they got stuck focusing on trying to fix the elevator trim issue and neglected to heed the overspend warning and take the aircraft out of military power, this issue was no doubt precipitated by the lack of proper information that Boeing had provided to pilots regarding the functioning of the MCAS system.
..The 737 MAX's larger CFM LEAP-1B engines are fitted farther forward and higher up than in previous models. The aerodynamic effect of its nacelles contributes to the aircraft's tendency to pitch up at high angles of attack (AOA). The MCAS is intended to compensate in such cases..
..MCAS was supposed to compensate for an excessive nose up angle by adjusting horizontal stabilizer before the aircraft would potentially stall..
..MCAS played a role in both accidents, when it acted on false data from a single angle of attack (AoA) sensor..
..elected to not describe it in the flight manual or in training materials, based on the fundamental design philosophy of retaining commonality with the 737NG..
..thus minimizing the need for significant pilot retraining..
..Thus, airlines can save money by employing and training one pool of pilots to fly both variants of the Boeing 737 interchangeably..
..As an automated corrective measure, the MCAS was given full authority to bring the aircraft nose down, and could not be overridden by pilot resistance against the control wheel as on previous versions of the 737..
- Fixing a problem (engine size/placement not analysed) with a more complex solution (MCAS). - Acting on only 1 sensor. - Not described in manuals. - Not able to override.
Text-book red flags. Definitely greedy managers that pushed towards this. However the engineers involved must have a bad taste (at Boeing and FAA). Engineers should take an oath like doctors do "Hippocratic Oath". The relationsship between business and engineering must be strictly defined. Compromises has to be taken, even in safety critical systems, but when taken it can't be the same business that can assess it OK. Engineers must be able to say categorically no and have it recorded outside business, without fear of losing jobs.
On the other hand for tall people (which I am not) who use window seats (which I don't), the A320 is worse though because the cabin wall curves in more at head level.
But, let's not compare apples and oranges. Concerns about safety doesn't kill people, it protects them. The 737NG has a very low accident rate, and if you're looking for a plane with a statically lower incident rate, the ERJ is your only other clear choice. This is regardless of the fact that the FAA only allows ERJs to land in low-visibility at 3/4 of US airports.
Who wrote this?
In bad weather certain aircraft rely on their radar altimeter to help guide them to the runway. It gives them an altitude they can use to decide to abort their approach that is more accurate than air pressure combined with their inertial system. This below link shows that within a given distance of 5G they are not allowed to rely on their radar altimeter for those approaches.
http://www.alpa.org/resources/aircraft-operations-radar-alti...
> When operating in U.S. airspace, the following operations requiring radio altimeter are prohibited in the presence of 5G C-Band wireless broadband interference
> Instrument Landing System (ILS) Instrument Approach Procedures (IAP) SA CAT I, SA CAT II, CAT II, and CAT III
Below is the link for the S-ILS RWY 36 for DFW that requires SA CAT II. At the bottom you can see "RA 107/12" which means the airplane can fly down to 107' on RA (Radar Altimeter) without seeing the runway. At 107', if they don't see the runway environment, they must abort the approach. This approach assumes a working Radar Altimeter. The 5G NOTAMS effect this approach.
https://resources.globalair.com/dtpp/globalair_06039I36LSAC2...
Below is the NOTAM for DFW affecting approaches. With this NOTAM an aircraft cannot execute the above approach, so if the weather is between 107' and 200' (the minimum for a regular ILS without RA), then they are not allowed to land at that airport - where before the 5G NOTAM they could.
This is the narrow band of bad weather conditions in which the 5G affects approaches at DFW for that runway, 93 feet.
In the NOTAM you will see the above approach "ILS RWY 36L (SA CAT II)" listed and "PROCEDURE NA [not available] EXC [except] FOR ACFT [aircraft] USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVES"
> FDC 2/3758 (A0495/22) - IAP DALLAS-FORT WORTH INTL, DALLAS-FORT WORTH, TX. ILS RWY 17C (SA CAT I), AMDT 11B ... ILS RWY 17L (SA CAT I), AMDT 7 ... ILS RWY 18R (SA CAT I), AMDT 8A ... ILS RWY 35C (SA CAT I), AMDT 3 ... ILS RWY 35R (SA CAT I), AMDT 4B ... ILS RWY 13R (SA CAT I - II), AMDT 9B ... ILS RWY 17R (SA CAT I - II), AMDT 23D ... ILS RWY 18L (SA CAT I - II), AMDT 3 ... ILS RWY 31R (SA CAT I - II), AMDT 15 ... ILS RWY 17C (CAT II - III), AMDT 11B ... ILS RWY 17L (CAT II - III), AMDT 7 ... ILS RWY 18R (CAT II - III), AMDT 8A ... ILS RWY 35C (CAT II - III), AMDT 3 ... ILS RWY 35R (CAT II - III), AMDT 4B ... ILS RWY 36L (SA CAT II), AMDT 4 ... PROCEDURE NA EXC FOR ACFT USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVES 2021-23-12, 2021-23-13. 19 JAN 05:00 2022 UNTIL 19 JAN 05:04 2024 ESTIMATED. CREATED: 13 JAN 05:05 2022
- 5G is bad because it is a Chinese tech and they can spy on us
to
- it interfere with our equipments
Looks like they learn, instead of admitting they are behind china in telecommunication tech, they now push the idea that it just is making our "old btw" tech unusable
Nice, the Western culture!
That said, this is Boeing's fault. They need to clean up their act ASAP, and it seems like they've been banking on the FCC covering up their mess and are now running around with their hair on fire.
A reasonable stopgap may be to simply not allow 5G towers to use the frequencies ranges in question within some radius of an airport (20 miles?) for a few years until Boeing fixes the problem.
""Airbus and Boeing have been working with other aviation industry stakeholders in the US to understand potential 5G interference with radio altimeters," Airbus said in a statement."
The information is all over the place (https://ecfsapi.fcc.gov/file/101041916430138/GN%20Docket%20N...)
I would flip their argument on its head and state that as altimeters are that critical, make sure they follow the spec to the letter.
It's, like other commenters said, as if your neighbour sends you an eviction notice for your own house because you are next to him.
5G has taken a tremendous amount of effort and multiple years of work -- people have spent a decade on this. Boeing decided to not follow the spec. I think I will switch to Airbus. ;)
tl;dr: if Boeing can not keep inside a spectrum for the altimeter what else have they "cheated on?"
Using the eviction notice metaphor , this is a developer building a stadium with sound system rocking your walls every night, because someone sold them a parcel too close for noise abatement.
Could you please (I am asking out of curiosity) provide information about other companies? All I find are about passed tests.
Your example metaphor is good I agree! The developer of the stadium here are the radio altimeters' manufacturer in question.
The 200 Mhz gap between bands had been known. They just didn't want to: a) fix their leakage b) buy the "neighborhood" ie the band.
They had multiple chances over more than 10 years now. And now they use the FAA to bail them out.
We have the expectation, especially whoever flies and uses altimeters directly, that they will be extremely robust. From what I have seen so far a lot of corners have been cut.
P.S. Wouldn't you double think before flying with some equipment that your undergraduate self (EE) would design better? Pay for more band, not with our lives.
P.S.2 Here's a quick article about Boeing FAA required changes https://www.aviationtoday.com/2022/01/26/faa-requires-boeing...
If we keep to the stadium metaphor and you want to use radar altimeter as the stadium... 5G is someone deciding to build a house after it's been known for decades that the stadium is there then deciding to complain about noise.
The radar altimeters are not the ones leaking, and no corners have been cut in fact. It's effectively "spec was changed without coordination, and now we have to do extra tests to verify that it's safe"
The auctions started if you scroll down the article since 2018 (outside the US) for the neighboorhood in question.
https://www.spglobal.com/marketintelligence/en/news-insights...
Nobody raised a flag then. And nobody tried to stop the auctions. FCC has full jurisdiction on this. The C band is the popular one as the article also stresses. Yes FAA complained in 2020 and tried to delay the auction.
To even get to the auction the 5G workgroup has been simulating these ranges since 2014 at least (from personal knowledge). There is no chance the engineers working in the neighborhood bands did not know as at least word of mouth was out for anyone doing RF, WiFi, or with interference channels.
If you look at the 2016 European 5G annual journal the 3.5Ghz area is mentioned. https://5g-ppp.eu/annual-journal/ (The bands 42 and 43 which are the ones on question where mentioned that is.)
In 2017 FCC did the RFC for the auction. This is the biggest auction ever. Aviation Spectrum Resources (ASRI) was testing and passing altimeters (initial test done and submitted 2019). FAA and various altimeter developers did nothing. (See https://5gamericas.org/wp-content/uploads/2021/07/Mid-Band-S...)
If you see the article I shared in prior post, FAA has approved radio altimeter models and has disproved others.
In 2011 there was an assessment of the neighborhood bands interference as part of what they called NTIA Fast Track evaluation. And they raised interference issues with current spectrum and practices. FAA and developers did nothing.
FAA needs to pay to properly deploy antennas like other countries have for years, in airports and/or have someone buy the spectrum. 40 countries did it right already.
Worst case, they had since 2011 to do this.
P.S. When you build and antenna/receiver you are the one responsible for staying in spectrum.
There is 200 mhz fallow. You can't just go around building devices that will get affected even with a 200 MHz buffer. Nobody is invading their spectrum.
5G has been in development for over a decade I think. It's been deployed in the real world since 2019. So what the fuck have the FAA and FCC been doing in that time? You would have thought someone would have actually determined whether 5G can interfere with one of the most popular commercial aircraft?
Really? No one checked? No one asked?
This has been a mainstream news story for 4 weeks.
And no one at the FAA or FCC has put a 5G antenna next to an 737 and even tried check? No one has put together pilots logs or looked at aircraft systems logs? And in that time presumably 100s of 737s have taken off and landed and flown over these?
At this point, we know 2 things: It's very unlikely this an issue or we'd have seen a lot of serious incidents probably including an actual crash AND we need a federal organisation that manages aircraft safety and another for communications including EM spectrum to avoid inference and we don't actually seem to have either.
I work with trading tech. Nothing complex or amazing. Just money, nothing safety critical. Sometimes things break or we have bugs. I can say a lot of things to my boss when something goes wrong, I can't say "It could be a massive problem, but I haven't bothered checking despite having 4 weeks to at least start" so I don't really know.
If they know there is an (intermittent, occasional) issue then ground the planes. Don't announce it, but cryptically and then do nothing and wait for a few 100 deaths.
If they know there isn't a problem then shut up.
And if they don't know, why the fuck don't they know after (at least) 4 weeks of testing. Can't they at least say all tests fine or 99% of tests fine or we crashed 4 planes but maybe the test pilots were just bad?
"They mostly did. They've been warning about this for 3+ years now (see this report from the FCC back in September and October 2019) https://ecfsapi.fcc.gov/file/102214765103/AVSI%20RA%20Interi...
"They couldn't have warned folks about more than a year or so sooner than that, because the spectrum bands for 5G hadn't even been fully decided prior to it. (The public notice of band reconfiguration only got announced back in May 2019)"
It's why everywhere else, there are either mitigations on 3.8-4.0GHz frequency use near airports, or the spectrum is not allocated to 5G comms.
Then, quite recently in the whole development, FCC decided to allocate 3.8-3.98GHz to telcos, without mitigations near airports