I find the following confusing:

Separately, the FAA on Tuesday published an airworthiness directive on the Boeing 777 and 747-8 airplanes that interference may affect multiple airplane systems using radio altimeter data. The directive does not prevent any operations at nearly all large U.S. airports. The FAA has approved alternative means of compliance for the airplanes.

Ref: https://www.reuters.com/business/aerosp ... 022-01-25/

Ok, we have a concern that is specific to 777 and 787, but it doesn't prevent operations at "nearly all" large US airports?

Edit: Thread attached to https://twitter.com/ByERussell/status/1 ... 4411471873 suggests that the result might be to not allow 787/777 to be dispatched to certain airports with 5G towers nearby, and to figure out which ones those are you need to dig through the forest of ADs that speak to limitations of individual airplane/altimeter combinations.

Here is the AD for the 747 and 777:

https://public-inspection.federalregist ... iling+list

Approaches and Landings in the Presence of Radio Altimeter 5G C-Band
Interference:

Dispatching or releasing to airports, and approaches or landings on runways, in U.S.
airspace in the presence of 5G C-Band wireless broadband interference as identified by
NOTAM is prohibited (NOTAMs will be issued to state the specific airports or
approaches where the radio altimeter is unreliable due to the presence of 5G C-Band
wireless broadband interference).

adipasqu wrote:

Here is the AD for the 747 and 777:

https://public-inspection.federalregist ... iling+list

Approaches and Landings in the Presence of Radio Altimeter 5G C-Band
Interference:

Dispatching or releasing to airports, and approaches or landings on runways, in U.S.
airspace in the presence of 5G C-Band wireless broadband interference as identified by
NOTAM is prohibited (NOTAMs will be issued to state the specific airports or
approaches where the radio altimeter is unreliable due to the presence of 5G C-Band
wireless broadband interference).

Rather misleading if that is all you are going to share. Boeing and Aircus received AMOC approval last week for multiple RA models including those utilized on the B777 family, B748 family



(3) AMOCs approved for AD 2021-23-12, Amendment 39-21810 (86 FR 69984, December 9, 2021) providing relief for specific radio altimeter installations are approved as AMOCs for the provisions of this AD.

Qantas744er wrote:

Rather misleading if that is all you are going to share. Boeing and Aircus received AMOC approval last week for multiple RA models including those utilized on the B777 family, B748 family



(3) AMOCs approved for AD 2021-23-12, Amendment 39-21810 (86 FR 69984, December 9, 2021) providing relief for specific radio altimeter installations are approved as AMOCs for the provisions of this AD.

I wasn't trying to be misleading, but since the AMOC's are only approved for a limited amount of time for now and we really don't know what they contain since the public can't access them, there wasn't any more context to quote directly pertaining to the AD that I linked to. The AMOC's have been discussed higher up in the thread.

DC 10s and 727s!! ;-)

M564038 wrote:

DC 10s and 727s!!

The MD-10 is on the list, so that seems to leave the 727 and the ERJ-135/140/145, I'm guessing?

adipasqu wrote:

Here is the AD for the 747 and 777:

https://public-inspection.federalregist ... iling+list

Not an AD but a request for comments on the proposed AD, right?

I'm getting the feeling that the FAA is going through painful contortions to try to keep everybody happy.

hivue wrote:

I'm getting the feeling that the FAA is going through painful contortions to try to keep everybody happy.

Is that a part of their job description?

Keep everyone happy, keep everybody unhappy. One of those odd constructions, opposites which mean about the same thing.

This will not end well...signed, Ayatollah So

When 5G rolled in out February, there was all this drama about airplanes crashing due to interference with radar altimeters. Haven’t heard or read anything since then. Even crazier is that the best 5G speeds that I have encountered has been at my home airport, SAT!

Some aircraft encountered problems but mysteriously none of them reported to the tower on arrival so...

Fred

Same thing that happened with Y2K doomsday predictions?

There are still issues. There are AMOCs out there for many runways for most aircraft types. There are fewer AMOCs for other aircraft types. For example, at one carrier the 223/320 has more AMOCs available than the E190, and the E190s can’t do RNP/cat2/3 approaches. There have been some anomalous issues associated with RA interference, such as spurious landing gear warnings when the aircraft is at say 4,000 feet with the gear up and the RA thinks it’s close to the ground due to the 5G interference.

EWRandMDW wrote:

Same thing that happened with Y2K doomsday predictions?

Somehow, I feel there's a large section of the a.net populous who may not get this reference.

EWRandMDW wrote:

Same thing that happened with Y2K doomsday predictions?

Y2K was mitigated through long and widespread awareness and efforts put into place to fix relevant programing codes in the few years in advance.
This.. is now being deal with with band aid fixes rolled out in two weeks when the news come that the 5G will actually be coming.

It's still out there but with mitigation in place. At my airline (757/767 operator) we have AMOCs for many of the airports we fly to, so normal operations continue. We do have a small subset of 767s that didn't receive FAA approval to use the AMOC airports. For those aircraft and at airports with AMOC, no CAT II/III, RNAV (RNP) or autoland.

flipdewaf wrote:

Some aircraft encountered problems but mysteriously none of them reported to the tower on arrival so...

Fred

The cell phone companies reported more precise location data for the towers to the FAA which allowed the FAA to reduce / remove a significant number of the restrictions. There are still a lot of issues out there, but most of them are performance limitations rather than prohibitions on operating. So a flight might be required to have some number of held seats based on the equipment type / airport combination.

Many aerospace companies are also developing / selling 5G filters that will protect the avionics that should "solve" the issue.

Here's a Phoenix NOTAM:

!PHX 01/073 PHX AD AP RDO ALTIMETER UNREL. AUTOLAND, HUD TO TOUCHDOWN, ENHANCED FLT VISION SYSTEMS TO TOUCHDOWN, HEL OPS REQUIRING RDO ALTIMETER DATA TO INCLUDE HOVER 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 DIRECTIVES 2021-23-12, 2021-23-13 2201190501-2401190501

A lot of abbreviations, but the bottom line is procedures relying on radio altimeter are not authorized without alternate means of compliance.

The FAA requested better data from the providers to establish which airports had potential issues and which didn't. Then created mitigation plans for those that did.

It was basically a standoff between FCC and FAA. FCC insisted there was no issue and referred to FAA as "ankle-biters". But FAA holds the authority and also held firm on no compromise for safety. So providers had to demonstrate impact with data.

It's still a big thing, but for a lot of the planes it is affecting, it's only for CAT II/III operations since CAT I can rely on the baro altimeter.

Where I work we have a pretty long list of pireps about 5G interference. There are AMOCs for our aircraft that lets us fly CAT II ops into certain airport where towers are far enough away.

Long story short, I think you won't hear much about it until you get an airport with close towers and a heavy fog bank. That's where things get screwy.

What problem?

FreeFlight is offering new direct-replacement radar altimeters that use custom DSP (Digital Signal Processing) to filter out potential interference with 5G tower signals. As of late-March of this year they were in the final stages of receiving FAA approvals, which is expected to be granted soon.

https://www.ainonline.com/aviation-news ... altimeters

LDRA wrote:

What problem?

See all above…

Also, the FCC has decided that they're going to crack down on receivers that have insufficient resiliency to interference.

From: https://arstechnica.com/tech-policy/202 ... equencies/

In her statement before the vote, FCC Chairwoman Jessica Rosenworcel said, "Receivers that are not sufficiently resilient [to interference] can make it more difficult to introduce additional services in the same or adjacent airwaves [and thus] diminish the spectral environment and shut out new uses before they even begin."

While the FCC isn't clear if it has the ability to regulate reception (much of their legal basis focuses around regulating transmission), they're going to study what their options are. However, whatever steps they take toward making things clearer around reception are an improvement, that is the crux of what got us into this pickle. Also both the FAA and the FCC should've been clearer about this to begin with.

This does bring up a related question, I wonder if the FAA ever will clean up the interference that comes from radio altimeters still functioning when they're on the ground. It'd seem trivial to start to require new equipment to stop transmitting when there is weight on the wheels.

BEG2IAH wrote:

WASHINGTON, May 24 (Reuters) - The Federal Aviation Administration (FAA) wants airlines to complete retrofits of some airplane radio altimeters that could face interference from C-Band 5G wireless service by the end of 2022, according to a memo seen by Reuters.

The FAA memo said following a May 19 meeting of airlines, manufacturers and wireless carriers that "a collective goal was set to complete" retrofits on some Embraer and Airbus planes by the end of the year. Another meeting is set for June 3.

The memo sets out a series of dates for actions by the aviation industry, including by June 1 asking airlines to "commit to purchase filters and installation kits." The FAA plans to develop a "tool to track and report progress in real time" by May 31, the memo says.

The FAA and altimeter manufacturers divided the U.S. commercial passenger airline fleet into four groups based on their tolerance to interference. Group 1 has the poorest performing altimeters and primarily consists of Embraer regional jets, while Group 2 is largely Airbus A320s, officials said.

The FAA wants 1,760 planes in Groups "1 and 2" to be retrofitted this year. None have been completed yet.

The memo also says retrofits should be completed for 4,800 Group 3 planes in 2023.

https://finance.yahoo.com/news/1-u-faa- ... 34609.html

Its good to see the FAA taking assertive steps that should've been taken a few years ago.

I'm curious if the memo in question. I found an AD in the federal register for 707, 717, MD10, MD11, and MD80 airplanes, but nothing covering the Embrarers.

Which Embrarers are in Group 1? E140/145 or does it include E170/175/190s?

It looks like only Reuters had access to the memo. I searched for it but found nothing.

it appears the airlines have another year to fix the affected altimeters.
Summary
https://arstechnica.com/tech-policy/202 ... g-signals/

details
https://public-inspection.federalregist ... -00420.pdf

(pg14) The FAA estimates that approximately 180 airplanes would require radio altimeter replacement and 820 airplanes would require addition of radio altimeter filters . No details on which altimeters need to be replaced.

ZBA2CGX wrote:

it appears the airlines have another year to fix the affected altimeters.
Summary
https://arstechnica.com/tech-policy/202 ... g-signals/

details
https://public-inspection.federalregist ... -00420.pdf

(pg14) The FAA estimates that approximately 180 airplanes would require radio altimeter replacement and 820 airplanes would require addition of radio altimeter filters . No details on which altimeters need to be replaced.

Please be aware that posting to a thread inactive for longer than six months requires moderator approval. As this is a noteworthy update, the thread bump is fine. Please check with us first next time!

✈️ atcsundevil

Transport Secretary Pete Buttigieg said on Tuesday that airlines were told the 1st July deadline would remain in place.

https://www.bbc.co.uk/news/world-us-canada-65465512

Airlines have warned that they will not be able to meet the deadline and may be forced to ground some planes.In a call with airline companies on Tuesday, Mr Buttigieg told them to work aggressively to retrofit their planes before the deadline.
Handy just before the 4th July.

Oh boy... great timing.

I remember the 777 and E jets were affected. I thought the A3xx, NG/MAX and 757/767 were okay?

Here is a link to the new FAA proposed rulemaking.

https://public-inspection.federalregist ... -09433.pdf

It appears that they are altering the definition of a compliant radio altimeter, and using a power spectral density (PSD) curve rather than a single sensitivity point as in the previous AD. In the immediate term, airlines would have to alter their AFM to indicate that this standard is now required for operations at airports that are not C-band mitigated.

This makes good engineering sense, as the altimeters would have greater assurance of resistance to interference by using a PSD curve. But it creates a new wrinkle for compliance.

SEAorPWM wrote:

Oh boy... great timing.

I remember the 777 and E jets were affected. I thought the A3xx, NG/MAX and 757/767 were okay?

The altimeter compliance requirement applies to all commercial transport aircraft. However there are additional limitations for 777 aircraft that utilize the altimeter for pitch control, as well as 747-8(F) aircraft that utilize the altimeter for tail strike avoidance.

You may be referring to the exemptions granted to most models at mitigated airports. The issue now is that the telecoms are ready to lift the requirements for mitigation at those airports, while the airlines are not prepared to meet the altimeter compliance requirements.

The PSD altimeter compliance requirement would be extended to February 1, 2024.

This has been dragging for a very long time... can't the telecom and airline industry work something out between themselves ? I'm with Pete Buttgieg on this... it's time for the companies involved to get on and solve the issue

It's a mess in terms of timing, as it occurred during the pandemic when suppliers were largely shut down. Now there is a huge demand for the altimeters, but not enough supply.

Also the FAA and FCC had a turf battle that confused signalling as to what would happen at the deadline, with both sides believing they would prevail. That resulted in a collision which is still not fully resolved.

davidjohnson6 wrote:

This has been dragging for a very long time... can't the telecom and airline industry work something out between themselves ? I'm with Pete Buttgieg on this... it's time for the companies involved to get on and solve the issue

Realistically it’s between the airlines and the radio altimeter suppliers. The suppliers built something non compliant, and the airlines are the ones who are affected. It’s just that they’ve been getting away with it for years.

As far as I know, all 777s have been made compliant. The real issue are the E-Jets, which are super common in the US.

USAirKid wrote:

davidjohnson6 wrote:

This has been dragging for a very long time... can't the telecom and airline industry work something out between themselves ? I'm with Pete Buttgieg on this... it's time for the companies involved to get on and solve the issue

Realistically it’s between the airlines and the radio altimeter suppliers. The suppliers built something non compliant, and the airlines are the ones who are affected. It’s just that they’ve been getting away with it for years.

Well, not exactly. 5G in the problematic spectrum is a relatively new thing. That said, this technology has worked safely and without interference for decades. The FCC and the telecoms are really the ones at fault here.

N1120A wrote:

USAirKid wrote:

Realistically it’s between the airlines and the radio altimeter suppliers. The suppliers built something non compliant, and the airlines are the ones who are affected. It’s just that they’ve been getting away with it for years.

Well, not exactly. 5G in the problematic spectrum is a relatively new thing. That said, this technology has worked safely and without interference for decades. The FCC and the telecoms are really the ones at fault here.

Nah. The radio altimeters have always been non-compliant, they just didn't have a neighbor until now that highlighted how they are non-compliant. The FCC has also given a fairly wide guard band between where the radio altimeters are supposed to operate and the 5G mobile operators band, and it still is an issue for the radio altimeters.

If this were property, it someone who built their home on the property line, then gets upset that when the city got around to selling the lot next to their property. When that property is built on they complain that "their" trees are torn down, because they were never on their property to begin with, and the verdant view is now a wall of a new home.

Radio altimeters went into planes designed in the 1990s were of technology of the 1960s, although by 1990s it could be reasonably predicted that radio spectrum would be in demand, and you should be staying in your allotted space. To top it off, the air framers, altimeter manufacturers, and airlines didn't take the issue seriously until the last moment, instead opting to try to get a series of unending extensions.

This sucks for the airlines, and they should lean on the air framers and altimeter manufacturers hard, upto and including legal action for delivering equipment that was not legal to operate in the US.

N1120A wrote:

Well, not exactly. 5G in the problematic spectrum is a relatively new thing. That said, this technology has worked safely and without interference for decades. The FCC and the telecoms are really the ones at fault here.

Read the thread (or google it). The altimeters were clearly faulty. They were (are) susceptible to interference from signals on frequencies well outside of their designated operating range and past a giant safety buffer. They extended the buffer to 400MHz, and some systems still failed to operate properly. To put that in perspective, the entire C-band in the US was supposed to be 500MHz, so the buffer they tried to implement was almost as large as the C-band itself. Normally a buffer in that range would be closer to 20MHz (as it was planned between 3.98-4GHz to separate C-band (mid) and satellite operators). .

This is a failure that was avoidable had these altimeters been designed and tested properly. I hope airlines sue those manufacturers to recoup some of their mitigation costs.

RDUDDJI wrote:

N1120A wrote:

Well, not exactly. 5G in the problematic spectrum is a relatively new thing. That said, this technology has worked safely and without interference for decades. The FCC and the telecoms are really the ones at fault here.

Read the thread (or google it). The altimeters were clearly faulty. They were (are) susceptible to interference from signals on frequencies well outside of their designated operating range and past a giant safety buffer. They extended the buffer to 400MHz, and some systems still failed to operate properly. To put that in perspective, the entire C-band in the US was supposed to be 500MHz, so the buffer they tried to implement was almost as large as the C-band itself. Normally a buffer in that range would be closer to 20MHz (as it was planned between 3.98-4GHz to separate C-band (mid) and satellite operators). .

This is a failure that was avoidable had these altimeters been designed and tested properly. I hope airlines sue those manufacturers to recoup some of their mitigation costs.

Because it seemed a bit large, I went digging where the interference testing with a 400MHz buffer came from. I didn't find it, it appears to be a guess off of a chart. The first mention of it is this:

dynamo12 wrote:

A 400Mhz guard band is absolutely ridiculous. If you cannot operate radio equipment with 400Mhz guard you have no business operating anything RF - period.

Let's be clear. Radio Alt STARTS at 4200 (and as another 200 to work with). These new bands are coming in somewhere around 3800.

400Mhz would get you laughed out of the room anywhere else. The idea that a radio altimeter needs 200MHz + 400Mhz (or more) on each side is absolutely ridiculous especially in this band area - that's nearly 1,000Mhz of bandwidth.

Normal guard bands might be something like 0.1Mhz to 20Mhz in other domains.

Then this was posted replying to dynamo12's post:

dennypayne wrote:

And yet according to the graph posted by kalvado, that’s the reality of what is happening. Fixating on what “should” be the case is useless at this point.

But as long as we’re talking “shoulds” - safety should be paramount over making money, and ideally the FCC and FAA should have collaborated earlier on this issue. But here we are…

And FWIW here is the chart from kalvado:

kalvado wrote:

zeke wrote:

kalvado wrote:

I can find no testing of 5G equipment being made for interference with other existing approved FCC equipment, aviation equipment is throughly tested for interference with other equipment.

Here is a good illustration of an issue (taken from https://www.aviationtoday.com/2021/01/1 ... -aircraft/ )

Problem is not with 5G contaminating spectrum, problem is with radio altimeters receiving signals they should be totally immune to. Slope of green lines on the figure should be almost vertical. Current design standards were acceptable when radio receiver was the only electronic device owned by an average household. They should had been updated by the end of 20th century.

So while the mask that the radio altimeter is using is definitely not filtering out signals over 400 mhz from its assigned band, its not necessarily evidence that testing was done that shows interference with a 400 mhz buffer, just that the receive mask is stupidly large.

An additional consideration is the difference in operational power levels between 5G and radio altimeter bands. 5G towers operate at about 100 times the power level of a radio altimeter.

Thus historically, altimeters have been optimized for sensitivity rather than the bandpass filtering that is now needed, in the presence of a much more powerful adjacent signal.

However as others have noted, this is a very solvable problem with modern RF components.

USAirKid wrote:

Because it seemed a bit large, I went digging where the interference testing with a 400MHz buffer came from. I didn't find it, it appears to be a guess off of a chart. The first mention of it is this:

It came from Arstechnica, who's been closely following this, and the FAA.

https://arstechnica.com/tech-policy/202 ... equencies/

Quote:

The 220 MHz guard band is actually 400 MHz in practice this year because AT&T and Verizon have not yet deployed above 3.8 GHz. Despite that unusually large buffer, the Federal Aviation Administration said that altimeters couldn't avoid receiving 5G transmissions and forced the carriers to delay the rollout originally scheduled for December 2021. The FCC had urged the aviation industry to fix their altimeters in February 2020 when the commission approved the spectrum for cellular use. The carriers' C-Band rollout eventually moved ahead but with additional temporary restrictions near airports.

The repeatedly delayed 5G implementation is occurring on July 1.

DOT Secretary Buttigieg indicates that 20% of US planes and 35% of international planes that fly to the US are not yet ready.

Jetblue has 17 A220s to retrofit still
United says all mainline are retrofit (no details on United Express)
Delta has 190 plans left still to do (All 220s, many 319s and 320s, a few 321s)

Do we have any details on which international airlines and types are/are not ready?

https://www.businessinsider.com/flights ... ieg-2023-6
https://www.reuters.com/business/aerosp ... 023-06-23/

https://www.cnn.com/travel/article/boei ... index.html

Even this one is not ready, currently in the UK, will be racing the deadline back.

CI 747F, 777 may not be ready
https://aviationweek.com/air-transport/ ... ation-plan
China Airlines told the agency it signed an agreement with an unnamed supplier in November. On Jan. 11, the supplier reported that “due to [a] parts shortage,” it cannot deliver needed equipment for the carrier’s Boeing 777 and 747-400 freighters by the FAA’s proposed deadlines.

This is so unnecessarily painful. Boeing has still not issued the AMOC for the 737. Maybe tomorrow.

It is absolutely insane, that the whole world limited 5G to frequencies not affecting radio altimeters used in aviation, while the US insisted on using the larger frequency band completely ignoring the danger to aviation.

And again you wonder, if the billion dollar businesses behind 5G and wireless telecommunication didn't leave some big checks behind at the FCC, while the FAA slept again when it should have been wide-awake...