FAA ADs re 5G interference

[Klauss]

Hi,
sorry, I have absolutely no more details......and google couldnīt find any further reference to the trial.
There should be a report out on it by the French Authorities, iīd say.... no idea, though, where to look for it.
K

Originally Posted by Sallyann1234

Unfortunately that test - or at least the report of it - is of no use without a mention of the frequencies that were used for the 5G transmissions. Were they in the new band 3.6 to 3.8GHz* which is of concern due to being nearer to the aeronautical allocation, or in the lower cellular bands e.g. 2.6GHz?

It is the potential conflict from nearly adjacent frequencies that is critical. 5G cellular in the lower bands, which has been in use for some time, poses no risk to airborne operations.

* individual national allocations may be different.

[Imagegear]

There is a large area of 5G at 3.5 Ghz around the town of Pamiers in the region of Cazaux in South West France. (The area identified in the Video posted above.)

5G at 3.5Ghz in France

Selecting the 5G button on the page will present both 700mhz (In Green) and 3.5gb (In Blue) just noting that it could be either that was used in the test.

Also the spectrogram display on the monitoring system in the helicopter was indicating 3.64 to 3.675 Ghz. I can only assume to be a range around 3.65 Ghz.

IG

[SeenItAll]

Originally Posted by Sallyann1234

Just to be clear, they are not in the same band. They are in adjacent allocations, with a small guard band in between.
.

The guard band provided by the FCC is not small. It is huge -- over 200 MHz.

[YRP]

Originally Posted by SeenItAll

The guard band provided by the FCC is not small. It is huge -- over 200 MHz.

200 MHz is not large, percentage wise.

Current technology allows building filters like that without too much difficulty. But when the radars were designed, it would have been quite challenging.

I suspect the radars were at the limits of contemporary technology at the time — which is why they used that frequency band, since nothing else but satellite stuff could use anything nearby.

As a result, it appears the existing radars are more susceptible to out of band interference than is now desirable.

[Sallyann1234]

Originally Posted by SeenItAll

The guard band provided by the FCC is not small. It is huge -- over 200 MHz.

The gap is wider - from 3800 - 4200 MHz in Europe. In the UK, the regulator Ofcom is looking at allowing other services into this band in addtion to existing fixed links and satellite services.

[WillowRun 6-3]

FAA Additional Information Dec. 23 '21

Flight Standards Service of FAA has issued SAFO - Safety Alert For Operators - 21007, 23 December 2021. Subject and Purpose sections quoted verbatim:
"Subject: Risk of Potential Adverse Effects on Radio Altimeters when Operating in the Presence of 5G C-Band Interference.
Purpose: This SAFO provides information and guidance to operators regarding the risk of potential adverse effects on radio altimeters when operating in the presence of 5G C-Band wireless broadband signals, and the role of Notice to Air Missions (NOTAMs) in identifying the geographic areas where certain operations requiring a radio altimeter are prohibited in the presence of 5G signals (in the C-Band) by Airworthiness Directives (ADs) 2021-23-12 and 2021-23-13."

Link to FAA website and the SAFO document:
SAFO21007, Risk of Potential Adverse Effects on Radio Altimeters when Operating in the Presence of 5G C-Band Interference (faa.gov)

FAA also issued an SAIB - Special Airworthiness Information Bulletin, AIR-21-18R1, "Risk of Potential Adverse Effects on Radio Altimeters"
Here is, verbatim, its opening paragraph:
"This Special Airworthiness Information Bulletin (SAIB) informs aircraft manufacturers, radio altimeter manufacturers, operators, and pilots of the planned deployment of wireless broadband networks in the 3700-3980 MHz bands (C-Band).1 C-Band wireless broadband deployment is permitted to occur in phases with the opportunity for operations in the lower 100 megahertz of the band (3.7-3.8 GHz) in 46 markets beginning as soon as December 5, 2021; however, the FAA does not expect actual deployment to commence until January 5, 2022. This SAIB recommends that radio altimeter manufacturers, aircraft manufacturers, and operators voluntarily provide to federal authorities specific information related to altimeter design and functionality, specifics on deployment and usage of radio altimeters in aircraft, and that they test and assess their equipment in conjunction with federal authorities. Results from that testing and assessment should be reported to the appropriate civil aviation authorities (CAAs) and spectrum regulators. The FAA is currently collaborating with the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) to assess the need for mitigation beyond the recommended action in this SAIB." (emphasis added)

Link to FAA website and SAIB:
AIR-21-18R1.pdf (faa.gov)

(This SLF/att'y credits FlightGlobal Daily Briefing (24 Dec. 2021) for noting this development.)

[Klauss]

Thanks for posting.
I find the list of potentially affected systems in the SAFO to be an eye-opener.
A spurious radio-altimeter indication and nuisance (?=!?!) TERRAIN callout might be one thing, could be handled by procedures/airmanship,
but a malfunctioning tail strike prevention system ? No idea what that can do in aircraft such as a 777 or 747-8.
Pilots canīt influece such systems, can they ? Least of all during flare/takeoff, when they are needed.
Maybe a simple īairport closed due to 5G interferenceī NOTAM text might be best.
K

[Sallyann1234]

From WillowRun's links it's clear that the FCC is well aware of the potential problem, since they are restricting the initial C band cellular to below 3.8 GHz. This allows a clear 400 MHz gap from the air radar band, the same as in Europe.

But this restricts the US cellular band to only 100MHz width, which is unlikely to satisfy their requirement long-term, particularly in cities. In Europe the cellular band starts lower at 3.6 GHz, giving a full 200MHz bandwidth.

As the document states, much more needs to be known about the radar equipment sensitivity to out-of-band signals, but it does seem there is no need for immediate safety concerns.

edit: changed an M to G

[turbidus]

What was scary about the SAFO as it contained sample NOTAM's....Autoland, HUD, SA CAT I / II, CAT II, III, or RNP AR...all NA due to 5G?!?!?!

ZHU AIRSPACE RDO ALTIMETER UNREL WI AN AREA DEFINED AS XXXNM RADIUS OF XXXXXXNXXXXXXXW (VOR/DME) SFC-5000FT AGL. HEL OPS REQUIRING RDO ALTIMETER DATA FOR OFFSHORE INSTRUMENT OPS, HOVER AUTOPILOT MODES, SAR AUTOPILOT MODES, AND CAT A/B/PERFORMANCE CLASS TKOF AND LDG NOT AUTHORIZED EXC FOR ACFT USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVE 2021-23-13

BDL IAP BRADLEY INTL, WINDSOR LOCKS, CT. ILS RWY 06 (SA CAT I AND SA CAT II), AMDT 13A… ILS RWY 06 (CAT II AND CAT III), AMDT 38A… RNAV (RNP) Z RWY 06, AMDT 1… RNAV (RNP) Z RWY 24, AMDT 1… PROCEDURE NOT AUTHORIZED EXC FOR ACFT USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G CBAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVE 2021-23-12

SPECIAL COOK CANYON RANCH, RANGER, TX. RNAV (GPS) RWY 17, ORIG...RDO ALTIMETER UNREL. AUTOLAND, HUD TO TOUCHDOWN, ENHANCED FLT VISION SYSTEMS TO TOUCHDOWN NOT AUTHORIZED EXC FOR ACFT USING APPROVED ALTERNATIVE METHODS OF COMPLIANCE DUE TO 5G C-BAND INTERFERENCE PLUS SEE AIRWORTHINESS DIRECTIVE 2021-23-12

[WillowRun 6-3]

FAA, Dep't of Transportation propose interim plan and solution

By letter dated 31 December 2021, the Secretary of Transportation and FAA Administrator have documented an interim plan and solution to the 5G interference issues. The letter is on Secretary Buttigieg's letterhead though it bears the signatures of both senior officials (something a lawyer would pause to note, but anyway) - here is the link to the FAA website and the letter:

DOT and FAA Letter to ATT and Verizon executives on 5G

For those possibly too uninterested or unconcerned to read it closely, the basic point of this development is to push back the start date for 5G service by these two companies by two weeks, to continue what evidently has been a constructive dialogue between FAA (and DOT to the extent the 'mother-ship' federal agency is involved at levels above FAA proper) and the two service providers (ATT and Verizon). Also, the letter outlines a way of segmenting the problem, so that some areas around certain airports would not see 5G introduction until more is known about potential interference modalities and solutions. There also is a role being pitched for AMOCs, Alternative Means of Compliance. It's just two pages, give it a read.

Not least, in the eyes of this SLF/attorney, there is nice language at the end about the predominant significance and critical importance of aviation safety in the United States. "Aviation nation" - kinda has a nice cadence to it, I think I could self-load to it.

[boaclhryul]

Politico: "AT&T, Verizon reject Buttigieg's plea to delay 5G launch amid warnings of aviation chaos" https://www.politico.com/news/2022/0...viation-526365

[WillowRun 6-3]

Jan 2, 2022 ATT & Verizon letter back to DOT & FAA

Politico article contains a link to the letter dated 2 January 2022 replying to the Dec. 31, 2021 letter from Buttigieg and Dickson. Even reading it for speed over accuracy, it's pretty evident that ATT and Verizon had their reply teed up and quite ready to be dispatched.
This volley in the exchange is both longer and more detailed than the government's letter a few days ago.

https://www.politico.com/f/?id=00000...f-fe3e997f0000

[WillowRun 6-3]

More on the intensifying dispute

More items for those interested in the play-by-play level of developments, as the date of January 5 looms large.
The U.S. airline trade association, Airlines For America, filed an emergency petition with the FCC seeking to delay the start of 5G service. (It's a full-blown legal document, although as is typically the case, reading the first few pages or sections would provide a good overview and most (if not nearly all) of the main points being argued.)
Link is from an FCC filings website:

Emergency Petition for Stay -- Final.pdf (fcc.gov)

Also, on Twitter, a very knowledgeable person has posted a couple of threads examining some of the technical issues (way over this SLF/atty's level of antenna and electromagnetic spectrum knowledge). @Satcom_Guru
One thread examines the 2020 RTCA report on these issues, which (if I'm getting the message correctly) the wireless carriers say has been debunked and discredited, while the airlines are continuing to rely upon it.

Perhaps most significant considering the source, the U.S. Representative who holds the chair of the Committee on Transportation and Infrastructure of the House of Representatives, Hon. Peter DeFazio (of Oregon) has issued this statement (from Committee website):

"In light of the fast-approaching deadline for deployment, Airlines for America has taken the prudent step of filing an emergency petition to stay 5G deployment. I support their efforts and urge both the aviation and telecom industries to continue working together to find a safe way to deploy 5G technologies. For years—and as recently as this fall-- I have urged the FCC to put aviation safety first and thoroughly examine all risks involved. We can’t afford to experiment with aviation safety. I’ll continue to work with the federal government and the aviation community to make sure we’re not putting corporate profits above the safety of our skies."
_________________

This is going to end up in a courtroom, one would forecast without great concern for overstatement.

Edit: After reading a good portion of A4A's Emergency Petition for Stay . . . well, bad call on my part, in response to kiwi grey's question way up-thread. That question was whether U.S. airlines might benefit from suing FCC. What I had not realized, or thought enough about to anticipate, is that there already has been extensive agency proceedings before FCC in this matter. The initial Report and Order granting licenses for 5G in the C-Band, followed by petition(s) for reconsideration, and other filings, extensive in scope and amount. The "aviation community" has presented extensive evidence to FCC - evidence which A4A's current Petition argues the FCC has inexplicably ignored (and unlawfully ignored).

So my earlier (flippant, perhaps) comments were wrong, because I took the question as addressing a lawsuit from scratch. That was, actually, very wrong. Also, the politics around this matter are a bit trickier than at first impression. Despite strong objections during the first portion of the agency proceedings (that is, before FCC), the auction of spectrum took place in early December 2020 - during the transition between White House administrations. Draw your own conclusions about whether or not cooler heads did prevail, or even could have prevailed, during that time period.
So, to go back to kiwi grey's inquiry.

Well, reading the A4A Emergency Petition - and KUDOS to the lawyers for anytime you see a brief with some catchable typos, you know the time-pressure they were under was killer, killer - I would say that the FCC is going to get a very severe thrashing in federal district court. Well worth the price of popcorn - and I'm buying, kiwi grey, because after further review, indisputable legal reasoning shows I made the wrong call. Cheers!

[Klauss]

practical: 5G is up and running

Thank you very much WillowRun and others for your postings - very interesting reading.
Just...why is this 5th of January such an important date ?
The popular OOKLA internet speed testing site shows lots and lots of commercially available 5G stations around the world, and also close to airports, like JFK.
So, the 5G horse is out of the stable - or is it ??
K

[Klauss]

Apologies, forgot a link: https://www.speedtest.net/ookla-5g-map

[Sallyann1234]

Originally Posted by Klauss

Thank you very much WillowRun and others for your postings - very interesting reading.
Just...why is this 5th of January such an important date ?
The popular OOKLA internet speed testing site shows lots and lots of commercially available 5G stations around the world, and also close to airports, like JFK.
So, the 5G horse is out of the stable - or is it ??
K

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.

[cattletruck]

From https://en.wikipedia.org/wiki/5G_NR_frequency_bands

C-Band frequencies are defined as n77, n78 and n79. The problem band is n77 which is quite a broad band, almost 1Ghz.

As I mentioned above, even though the mobile phone telecoms are brutally competitive with each other they have always centred their business around growth which also means not killing off their customers. I'm sure by their very competitive nature we will see them pursuing the FCC for any compensation they are entitled to.

[Sallyann1234]

There is no suggestion that all of n77 will be used for cellular. That is very unlikely for the foreseeable future.
In Europe only the the n78 sub band is to be used, with an upper limit of 3.8 GHz.

The problem in the US is that FCC has defined an upper limit just below 4.0 GHz, much closer to the air radar band. However they seem to be restricting initial assignments to below 3.8 GHz , which is a sensible move.

[Luc Lion]

The RTCA document quoted above (and hereafter) gives a good deal of contextual information and of explanation on how interferences can jeopardise radar altimeter operation.
However is does not give much numeric information and it is considered as discredited by some stakeholders.
https://www.rtca.org/wp-content/uplo...Altimeters.pdf

The following document from the ITU gives more numeric information and its publication date (02/2014) makes it more resistant to discredit.
https://www.itu.int/dms_pubrec/itu-r...2-I!!PDF-E.pdf

I'd like to highlight 3 pieces of information contained therein :
- the ITU recommendation for RA filters (ITU-R SM.337) : 24 dB per octave (or 80 dB per decade) with a maximum of 40 dB ; this is a 4th order filter (or four stages filter).
I checked the "paper" specifications of 2 radar altimeters ; they comply with the 80 dB per decade recommendation.
- the front-end overload level of tested actual radio-altimeters that ranged from -30 dBm (at best) to -56 dBm (at worst).
It means that these altimeters are overloaded with interference when their cumulated power is above 1 microWatt (1 10^-6 W) for the best device or above 2.5 nanoWatt (2.5 10^-9 W) for the worst, that power being measured after reduction by the input filter. (note: 0 dBm = 1 milliWatt, thus -30 dBm = 10^-3 x 1 milliWatt = 1 microWatt)
- the in-band sensitivity to interference noise is only 6 dB below thermal noise (probably caused by the large width of the band)

Let's put these numbers in perspective:
A signal from a 5G base station, at the frequency of 3.8 GHz, will overload the altimeter with -30 dBm overload characteristics if the plane antenna receives it with a power exceeding 2.2 microWatt. (I ignore cable losses).
For the worse device with -56 dBm overload characteristics, only 0.0056 microWatt will suffice to overload it.

If the same computation is made with a signal at 3.98 GHz, the best device will be overloaded with a power of 1.54 microWatt and the worse with a signal of 0.0038 microWatt.
So, allowing the frequency to step from 3.8 GHz to 3.98 GHz has the same effect as allowing the emitted power to increase by a factor 1.45 or it can be balanced by reducing the emitted power by that ratio 1.45.
We also see that the quality of the high frequency operational amplifiers used within or after the 4 stages filter is playing a much more important role than the cut-off frequency of the 5G band ; the factor between the best and the worst device is 400 !

[WRONG]A typical 4G antenna emits a 40W signal which gives slightly under 1 mW/m2 (1 milliWatt) of radiated power at 100 meters (note: the signal is not emitted in all directions of the full 4pi solid angle).
If a 5G antenna emits with the same power, a signal at 3.8 GHz is 500 times too powerful for the -30dBm radio-altimeter placed at 100 meters and about 200,000 times too powerful for the other one.
However, at 2.5 kilometers, it becomes acceptable for the best device.
[/WRONG]
Apologies: the paragraph above is wrong : I mistakenly made calculations that assume a 1 square meter antenna for the radar altimeter. That's way too much. I found RA antennas with surfaces of 0.01 m2 and 0.025 m2. For calculation examples, I'll associate the larger antenna with the RA having an overload threshold of -30 dBm and the smaller one with the RA having -56 dBM,
If a 5G base station emits a 40W signal at 3.8 GHz that is received by a radar altimeter at 100 meters distance, the power transferred through the antenna is about 25 microWatt which is a bit more than 10 times too powerful for the first radar altimeter. Increasing the distance to 300 meters or more will reduce the signal below threshold. For the second altimeter, the power transiting through the antenna is around 2000 times too powerful. For that one, the distance needs to be increased to 5 km. So, the size of the antenna can explain a part of the overload characteristics, but not all of them.

[Sallyann1234]

The transmitter power limits in Europe are given in this EU document:

relevant technical conditions applicable to the 3 400-3 800 MHz frequency band

I don't have a reference for the FCC power limits, but I expect this will be available somewhere.