5G working already, only C-Band new
 

Thank you very much for the clarification, Sallyann1234.:ok:


QUOTE=Sallyann1234;11164417]To clarify the issue once again, there is nothing magic about 5G transmissions that threatens aviation.

5G cellular been operating safely for a couple of years or more in many countries, as shown in the map you linked. Virtually all 5G cellular currently operates in existing frequency bands. I'm using 5G to post this message, on a 2.6 GHz band network.

The potential problem is that cellular systems are now being licensed in a new frequency band between 3.6 and 4.0 GHz - the so-called C band. The exact frequencies vary according to individual country regulations. It is this frequency band which is at issue, and any modulation method in this band whether 2G 3G 4G 5G might possibly be a problem for aircraft radars that respond in this band.

Can we please not conflate 5G with C band. This only confuses the issue, as you have demonstrated.[/QUOTE]

I'm not going to argue with the rest of your maths as I am unqualified to do so but the 1mW reference is 0dBm, not 1dBm. (1 X 10^0)

Thanks for the correction.
Sorry, it was hastily written.
The point I wanted to make was that there is quite probably ample room for balancing measures, like computing a safe distance between the base ground station and the path of the plane or like capping the total radiating power of the base station in the C band.

Also, a part of the problem is the lack of formal minimal specifications for radar altimeters.
If a minimal slope for the pass-band filter was defined (like the ITU recommendation of 24 dB per octave) and if a minimum overload level (in mW/m2 or in dBm/m2) was defined, it would be much simpler to specify the conditions of immunity from interferences caused by 5G ground stations.

Your calculations need to take full account of antenna beamwidths, which are important in link calculations.

The cellular antennas generally radiate in the horizontal plane or with a downward tilt, so when the aircraft is at its nearest, directly above, it will receive little signal. Conversely, when the aircraft is approaching the cell site and may if low enough be within its beam, the radar antenna is looking downwards and not at the cell site.

The worst calculated case of the two antennas looking directly at each other is extremely unlikely to happen.

You are quite right for the cellular antennas radiating lobes.
However, the reception cone for radar altimeter antennas is quite large : between 35° and 60° of cone aperture for the 3dB (half power) cone.
Here is a datasheet example of such an antenna ; it announces a minimum of 45° in roll angle and 40° in pitch.
https://www.sensorantennas.com/wp-co...7-2002-121.pdf

So, basically, a plane which is turning final with a 25° bank angle at 2000 ft height is sensitive to radio beams coming from more than 1.7 km or 1 sm from the outer direction of the turn (2000 ft x tan(45°+25°)).
And if we accept a gain loss of 10dBi, it probably extends to several statute miles away.

That's an interesting link, thank you.

But taking your example, at 2,000 feet the signal from a cellular antenna, most likely with a downtilt at almost ground level a mile away, should be extremely small. It shouldn't be too difficult to engineer the cell sites accordingly.

I agree with you : mitigation measures ARE possible

Another delay in US rollout:

https://www.bbc.com/news/business-59856063

This issue is not going to be resolved by letters back and forth, or by yet another short delay.
As discussed above this is not going to be resolved just by calculation. It needs practical tests.

How hard would it be for Verizon to set up a cell site on the approach to a USAF base, and have the FAA run some test flights? It should have happened months ago, and if it has where are the results?

Not All Direct Radiation
 

Previous discussion covers direct radiation from the cell tower to the RA antenna, but we are talking about C band which reflects from terrain, structures and conveyances.

Reflected radiation from a cell tower may also be received by the RA antenna. The potential signal strength needs to be assessed. Also different sites may produce different reflection patterns.
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real world tests needed
 

Hi, I´d be all for this idea. The French helicopter tests ((somewhere up in this thread)) were a step in the right direction, but I couldn´t find a proper report on them.
Yes, a real world C-band 5G system at a known location, like a USAF base, and then have airplanes go by ....when it´s CAVOK, fine weather.

The problem with a single serie of tests is that it will only be valid for the radar altimeter type installed in the testing aircraft, and for the same antenna fit.
The lack of radar altimeter specifications results in having different electronic characteristics for each altimeter type.

I believe that this issue will only be overcome if each altimeter maker provides the authorities with the results of standard tests on the interference immunity of their device : standard size and gain of the supported antennas, characteristics of their band filter, saturation curve of their first amplification stage vs frequency, supported in-band interference and noise level, etc.

Um, maybe I am naive (maybe??) but are these not data that manufacturers would have needed to supply in order to get their devices certified for installation in airframes?

I believe the FAA have access to a variety of aircraft. Of course one type alone would not be sufficient.
But why is nothing practical apparently being done? Is everyone waiting for someone else to make a move?

Report in The Wall Street Journal for edition published Jan. 6 2022 (and on WSJ website presently) indicates that DOT and FAA negotiated a deal with the two wireless carriers based on a "term sheet" reportedly reviewed by WSJ. Would be interesting reading, most likely.

U.S. DOT and FAA have (per the article) agreed not to seek or demand further delays. In addition to the current two-week delay, the federal authorities accepted the limitations most recently proposed by ATT and Verizon.

Without seeing the "term sheet" (and having any technical information in it explained properly), it is a guess to say that some plans appear to have been outlined, at least, for engineering, testing or other technical steps toward validating lack of interference or extent of any potential interference that does exist or might exist.

The major passenger and cargo airline trade group, Airlines for America, reportedly has elected to hold short of filing in federal court (presumably motion papers for a TRO, Temporary Restraining Order - though it's an easy call that this thread has already overstayed any welcome that might have existed for lawyer-speak, let alone more details about that fascinating federal procedure topic, "How to Stay an Agency Order When a Reconsideration Petition Still Is Pending").

FAA website on this subject
 

FAA has created a webpage devoted to "5G and Aviation Safety". Information posted at present includes FAA position that system operational characteristics in France are not the same as in the U.S., and that risks to flight safety identified (in various written pieces) by the "aviation community" will continue to be present, even with the mitigation steps recently agreed to.
Website also contains links to prior FAA statements and related documents.

5G and Aviation Safety | Federal Aviation Administration (faa.gov)

What's truly interesting about this is that incumbent services should enjoy protection from harmful interference from new services regardless of whether said interference is intentional or not. This is a first that a national spectrum management agency has thrown their hands in the air and allowed a new service to potentially disable a safety of life critical system.

Having said that, it is sadly also completely in line with the level of incompetence and disregard for established procedure we have seen over the past years at the FCC.

A Wireless Industry tech brief
 

As has been widely reported since it was announced in late December (the 22nd), the three major trade associations most directly involved have supposedly begun an effort to "work collectively to identify a path forward." Those associations were, of course, Airlines for America (A4A), Aerospace Industries Association (AIA), and Cellular Telecommunications Industry Association (CTIA) (see post #38 above).

Well, a little further poking around on internet resources and a technical brief by CTIA showed up. It's lengthy and detailed, but I'm posting it here anyhow...... because the conflict or, at least, disagreement about the bona fides of the safety concerns cited by FAA is a quite sharp disagreement, or conflict.

An SLF/attorney isn't going to comment on the technical matters. But -- reading the CTIA technical brief, its treatment of the bona fides of safety factors on approaches and missed approaches..... wouldn't that be within somebody else's expertise? And isn't there a factor in aviation system safety thinking that insists upon getting all the right answers first, rather than relying on a legal and regulatory-agency process to find answers that are then taken as necessarily right? (Also, the tech brief refers to "Aviation" as if it is a monolithic, unified sector, which isn't the case.)

The CTIA technical brief:
210903-CTIA-Ex-Parte-5G-Aviation-Technical-Annex.pdf

(Couple of days ago, Wall Street Journal posted an editorial scoring (I mean, commenting with heavy negativity) the Biden Administration's handling of this situation, and not excluding the Secretary of DOT or Administrator of FAA from this criticism. But for reasons WSJ doesn't have to explain, the editorial piece appeared just on the website, not in the print edition or its electronic iteration. Not dispositive of anything, but always fun to see "the business world" take on dueling heavyweight sectors of the economy.)

Thank you for the CTIA assessment, WillowRun 6-3. It´s as described, as study that shows up possible faults at other studies....in great detail. Some , rather astonishing, and so even to one not fully familiar with dB and other radio-science things.

I fully support your question about the safety : ....And isn't there a factor in aviation system safety thinking that insists upon getting all the right answers first.....
That´s how it used to be. Airbus and Boeing bend airplane wings until they break, to be shure that the right answers were given by the computer models, even at 2.5 times design load, or so, for example.
That kind of thinking would lead to tests, real world test of real aircraft flying over and near 5G towers transmitting at higher than nominal power to confirm that everything was safe - with a couple of passenger phones working in the aircraft in normal mode, not airplane mode. Yes, the passenger devices should all be in a airplane - safe mode, but with 2-300 passengers and at least as many phones and what not...who believes in 100% correct switching ?

That beeing said, the thinking seems to have changed. safe until proven dangerous ....that´s the new mantra, it looks like. EASA has a Safety Info Bulletin here: https://ad.easa.europa.eu/ad/2021-16
In that, they write: -quote- At this stage, no risk of unsafe interference has been identified in Europe. -unqoute-

That´s comforting .... until you consider the wing-bending example above. In analogy, it might be that ´airplanes are safe as no case of a wing breaking has been observed´.....because they just didn´t encounter any turbulence yet.

Slightly strange change of thinking.

So, I´d really like to see some real-world tests to enshure that 5G , operated with US paramaters, including some faults in antennas + aircraft, is safe. Some towers have to be put up, switched on, and aircraft + helicopters need to fly .

K

I can't disagree with Klauss.

Allowing C Band cellular except near airports is fine for normal airline operations, but what happens when an airplane has a distress condition and is off course? It may be flying close to cell sites, perhaps on a hilltop where they are often sited, and be deprived of height information at the very time when it is most vital.

And how does this help with low level operations over urban areas with a high density of cellular activity?

This really does seem another case of "We'll try it and see if it works". And we all know where that has led to recently.