Boeing12345 wrote:

Thales ERT-530 and -540 is now AMOC approved as well.

For those wondering (like me, who just did some googling), AMOC is "Alternative Method of Compliance" and a FAA document I googled said "The proposed AMOC must include specific conditions that would address the unsafe condition (e.g., by providing information substantiating that certain aircraft or altimeter models are not susceptible to C-Band radio frequency interference)."

In essence, there has been a workaround for the issue on the books all along, just waiting for people to invoke it.

Again, it's not clear what standard FAA is applying when deciding to accept the information that substantiates that the RADALT is not susceptible to C-Band RFI. I presume they aren't setting too high a bar if they can tick the box in just a few day's time.

32andBelow wrote:

Hasn’t the problem the whole time been we don’t know cus we haven’t checked. Which makes this thing so baffling?

It appears you are right. We've had these rounds of chest pounding if not willy waiving, and all that was needed was some clarity on how to file an AMOC and what FAA would or would not approve as Alternative Method of Compliance. Voila, a large percentage of the problem has disappeared.

32andBelow wrote:

So to recap.

The band was auctioned off years ago.

The airlines and faa new about this years ago.

Then att and verizon turned their towers on after saying they were going to for months and weeks

And then all the altimeters got approved within 24 hours of that?

Similar claims have been repeated multiple times in this thread. However, when I look for confirmation of the claims, what I find instead is the FCC saying the C-Band auction was less than a year ago:

https://www.fcc.gov/document/fcc-announ ... nd-auction

What was actually happening years ago were the initial discussions over re-allocating part of C-band to mobile wireless telecom. The aviation industry did convince the FCC early on that 4 to 4.2 GHz were too close for the higher power telecom use and would definitely cause interference, but there were still questions about what would happen with telecom in the 3.7 to 4 Ghz range.

Although the aviation industry wasn't itself using the 3.7-4 GHz space previously, the existing licensed uses (satellite transmissions) were very low power and the radar altimeter receivers face away from the satellites, so they did not cause harmful interference with the radar altimeters. Therefore, there had so far been no requirement to update receiver designs to be able to handle higher power transmissions in that adjacent low C-band spectrum, and they were able to be certified to a high design assurance level (A).

The FCC's proposed changes in licensed use altered the operating conditions those certifications were based on, so even with the extra frequency margin, the aviation industry continued its assessment of the interference risks and continued to comment on the FCC notices of proposed rulemaking urging a cautious approach to finalizing the plans to relicense 3.7 - 4 GHz, especially since there were safety implications to trying to move too quickly.

How did the FAA respond to those calls for caution?

They offered the satellite operators $10 billion to significantly speed up vacating their licenses for 3.7 - 4 GHz compared to the previous plan, thereby reducing the time the aviation industry thought they had to investigate and solve the problem down to from 3.5 years down to 1.5 years:

https://docs.fcc.gov/public/attachments ... 4655A1.pdf

Separately, I've been trying to understand some of the technical details being discussed. RF design is well outside my area of expertise, but I think I've been able to piece together a few additional details.

As far as I understand, there's two sides to any interference issue: one is the sensitivity of the radar altimeter receivers to out-of-band-interference (signals not in its intended reception range). The receivers are filtered, but while the common assumption is a band pass filter simply eliminates signals outside of a specified range, in reality it attenuates the signal with increasing effectiveness the further you get from the nominal edge. However, that attenuation might not be total unless you get very far from the passband.

Likewise, transmitters do not simply have a frequency bandwidth exactly at their nominal range. They also have a falloff of decreasing power at progressively further frequencies. They transmit some out-of-band interference. That is, of course, "prohibited" in simple terms, but prohibited here means there is a maximum threshold the transmitter has to comply with.

Some people in this thread have commented about experience with electronics that successfully operates with very small frequency margins. My understanding is that experience with two-way wireless links that operate at similar power levels does not translate well to the conflict we have here between devices of very different power levels.

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

As a final note, I also found a fair amount of technical information on radar altimeters here that some others may find interesting:

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

iamlucky13 wrote:

32andBelow wrote:

So to recap.

The band was auctioned off years ago.

The airlines and faa new about this years ago.

Then att and verizon turned their towers on after saying they were going to for months and weeks

And then all the altimeters got approved within 24 hours of that?

Similar claims have been repeated multiple times in this thread. However, when I look for confirmation of the claims, what I find instead is the FCC saying the C-Band auction was less than a year ago:

https://www.fcc.gov/document/fcc-announ ... nd-auction

What was actually happening years ago were the initial discussions over re-allocating part of C-band to mobile wireless telecom. The aviation industry did convince the FCC early on that 4 to 4.2 GHz were too close for the higher power telecom use and would definitely cause interference, but there were still questions about what would happen with telecom in the 3.7 to 4 Ghz range.

Although the aviation industry wasn't itself using the 3.7-4 GHz space previously, the existing licensed uses (satellite transmissions) were very low power and the radar altimeter receivers face away from the satellites, so they did not cause harmful interference with the radar altimeters. Therefore, there had so far been no requirement to update receiver designs to be able to handle higher power transmissions in that adjacent low C-band spectrum, and they were able to be certified to a high design assurance level (A).

The FCC's proposed changes in licensed use altered the operating conditions those certifications were based on, so even with the extra frequency margin, the aviation industry continued its assessment of the interference risks and continued to comment on the FCC notices of proposed rulemaking urging a cautious approach to finalizing the plans to relicense 3.7 - 4 GHz, especially since there were safety implications to trying to move too quickly.

How did the FAA respond to those calls for caution?

They offered the satellite operators $10 billion to significantly speed up vacating their licenses for 3.7 - 4 GHz compared to the previous plan, thereby reducing the time the aviation industry thought they had to investigate and solve the problem down to from 3.5 years down to 1.5 years:

https://docs.fcc.gov/public/attachments ... 4655A1.pdf

Separately, I've been trying to understand some of the technical details being discussed. RF design is well outside my area of expertise, but I think I've been able to piece together a few additional details.

As far as I understand, there's two sides to any interference issue: one is the sensitivity of the radar altimeter receivers to out-of-band-interference (signals not in its intended reception range). The receivers are filtered, but while the common assumption is a band pass filter simply eliminates signals outside of a specified range, in reality it attenuates the signal with increasing effectiveness the further you get from the nominal edge. However, that attenuation might not be total unless you get very far from the passband.

Likewise, transmitters do not simply have a frequency bandwidth exactly at their nominal range. They also have a falloff of decreasing power at progressively further frequencies. They transmit some out-of-band interference. That is, of course, "prohibited" in simple terms, but prohibited here means there is a maximum threshold the transmitter has to comply with.

Some people in this thread have commented about experience with electronics that successfully operates with very small frequency margins. My understanding is that experience with two-way wireless links that operate at similar power levels does not translate well to the conflict we have here between devices of very different power levels.

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

As a final note, I also found a fair amount of technical information on radar altimeters here that some others may find interesting:

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

And at the end of the day the faa approved all the altimeters 24 hours after the towers went on instead of in the weeks or months before. Att and Verizon were totally right to force their hand here. They would have lollygagged forever

So much drama about impeding doom, and now almost all Airbuses are already approved 24 hours after launch, some Boeing's also are. So, why this was not done year or two ago? FAA continues to look like a joke.

miegapele wrote:

So much drama about impeding doom, and now almost all Airbuses are already approved 24 hours after launch, some Boeing's also are. So, why this was not done year or two ago? FAA continues to look like a joke.

It is a joke, the B737Max, the minimum rest for the FA taking like 3 years to be implemented, the 5G.

The USA has stopped being part of the “first world” for a while now, heck we even got nepotism in the white house at some point.

Revelation wrote:

Boeing12345 wrote:

Thales ERT-530 and -540 is now AMOC approved as well.

For those wondering (like me, who just did some googling), AMOC is "Alternative Method of Compliance" and a FAA document I googled said "The proposed AMOC must include specific conditions that would address the unsafe condition (e.g., by providing information substantiating that certain aircraft or altimeter models are not susceptible to C-Band radio frequency interference)."

In essence, there has been a workaround for the issue on the books all along, just waiting for people to invoke it.

Again, it's not clear what standard FAA is applying when deciding to accept the information that substantiates that the RADALT is not susceptible to C-Band RFI. I presume they aren't setting too high a bar if they can tick the box in just a few day's time.

32andBelow wrote:

Hasn’t the problem the whole time been we don’t know cus we haven’t checked. Which makes this thing so baffling?

It appears you are right. We've had these rounds of chest pounding if not willy waiving, and all that was needed was some clarity on how to file an AMOC and what FAA would or would not approve as Alternative Method of Compliance. Voila, a large percentage of the problem has disappeared.

My impression is that, as it is typical these days, FAA set AMOC bar at a tripping hazard level. No information on what exactly is approved in terms of conditions. Are all previously authorized weather within existing minimums - airport (with reduced coverage areas?) - airplane with AMOCed equipment combos still authorized? Could be that approvals are conditional, on "even if it doesn't work, it is not a big deal" basis.
There is basically a total lack of information - both legal and technical, which is unfortunately typical for industry these days. I am not sure what is being hidden - actual trade secrets or lack of competence.

Seems like VN is silently replacing the B789 by the A359 on its SGN-LAX route.
No formal or public statement from VN yet, but the route is indeed operated entirely by the B789 since the beginning (launched weeks ago) and now the A359 is taking the job.

https://www.flightradar24.com/data/aircraft/vn-a899

iamlucky13 wrote:

32andBelow wrote:

So to recap.

The band was auctioned off years ago.

The airlines and faa new about this years ago.

Then att and verizon turned their towers on after saying they were going to for months and weeks

And then all the altimeters got approved within 24 hours of that?

Similar claims have been repeated multiple times in this thread. However, when I look for confirmation of the claims, what I find instead is the FCC saying the C-Band auction was less than a year ago:

https://www.fcc.gov/document/fcc-announ ... nd-auction

What was actually happening years ago were the initial discussions over re-allocating part of C-band to mobile wireless telecom. The aviation industry did convince the FCC early on that 4 to 4.2 GHz were too close for the higher power telecom use and would definitely cause interference, but there were still questions about what would happen with telecom in the 3.7 to 4 Ghz range.

Although the aviation industry wasn't itself using the 3.7-4 GHz space previously, the existing licensed uses (satellite transmissions) were very low power and the radar altimeter receivers face away from the satellites, so they did not cause harmful interference with the radar altimeters. Therefore, there had so far been no requirement to update receiver designs to be able to handle higher power transmissions in that adjacent low C-band spectrum, and they were able to be certified to a high design assurance level (A).

The FCC's proposed changes in licensed use altered the operating conditions those certifications were based on, so even with the extra frequency margin, the aviation industry continued its assessment of the interference risks and continued to comment on the FCC notices of proposed rulemaking urging a cautious approach to finalizing the plans to relicense 3.7 - 4 GHz, especially since there were safety implications to trying to move too quickly.

How did the FAA respond to those calls for caution?

They offered the satellite operators $10 billion to significantly speed up vacating their licenses for 3.7 - 4 GHz compared to the previous plan, thereby reducing the time the aviation industry thought they had to investigate and solve the problem down to from 3.5 years down to 1.5 years:

https://docs.fcc.gov/public/attachments ... 4655A1.pdf

Separately, I've been trying to understand some of the technical details being discussed. RF design is well outside my area of expertise, but I think I've been able to piece together a few additional details.

As far as I understand, there's two sides to any interference issue: one is the sensitivity of the radar altimeter receivers to out-of-band-interference (signals not in its intended reception range). The receivers are filtered, but while the common assumption is a band pass filter simply eliminates signals outside of a specified range, in reality it attenuates the signal with increasing effectiveness the further you get from the nominal edge. However, that attenuation might not be total unless you get very far from the passband.

Likewise, transmitters do not simply have a frequency bandwidth exactly at their nominal range. They also have a falloff of decreasing power at progressively further frequencies. They transmit some out-of-band interference. That is, of course, "prohibited" in simple terms, but prohibited here means there is a maximum threshold the transmitter has to comply with.

Some people in this thread have commented about experience with electronics that successfully operates with very small frequency margins. My understanding is that experience with two-way wireless links that operate at similar power levels does not translate well to the conflict we have here between devices of very different power levels.

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

As a final note, I also found a fair amount of technical information on radar altimeters here that some others may find interesting:

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

You're certainly right, more power from the other guy makes it more difficult to deal with. However, keep in mind - low power Bluetooth and microwaves often coexist in the same kitchen, and that is a much higher threshold to clear. Same for GPS receivers in cell environment - GPS signals are way weaker than anything in radalt world, while frequencies are pretty packed as well.
One take-home message from the pdf - many devices do not have crystal oscillators as stable frequency sources, those few which have do not bother to stabilize them. That alone dates designs into a stone age.

Does anyone here have a list of airports that are currently affected? I might have missed a post, and to be honest, this is only one of maybe three websites I even spend time with. My google time goes down as I age.

That being said, I am leaving Kauai tomorrow (I know, why?!) and landing SAT after changing planes, and winter weather is about to hit. It is also where i know for fact that CAT II is a maybe due to lights, PMI, and lack of give a darn. Long question short, is SAT on the 5G crap list?

XRadar98 wrote:

Does anyone here have a list of airports that are currently affected? I might have missed a post, and to be honest, this is only one of maybe three websites I even spend time with. My google time goes down as I age.

That being said, I am leaving Kauai tomorrow (I know, why?!) and landing SAT after changing planes, and winter weather is about to hit. It is also where i know for fact that CAT II is a maybe due to lights, PMI, and lack of give a darn. Long question short, is SAT on the 5G crap list?

https://cms.faa.gov/sites/faa.gov/files ... ment_0.pdf

SAT is there in this list.

iamlucky13 wrote:

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

Good points. A few brief comments about the 5G cell towers from someone formerly into spectrum management.
Although the maximum power may be 100W, the system's power control functions always reduce the power on any individual handset connection to the minimum needed to keep the connection alive with an acceptable bit error rate. Which typically is milliwatts or a few watts. Full power is typically used only briefly at connection establishment or when the handset is at the far edge of a large cell. This is a basic function in order to keep the same-channel interference down within the system (i.e. at the next same-channel base station/cell tower).
5G introduces a new "NR" radio interface which includes directional beam forming. This may be a double edged sword, if you think of an approaching aircraft where passengers try to check in to their networks and thereby make beams point towards the aircraft and its radio altimeter antenna. However, the power control still reduces the beams' power to the minimum required. The upside is that the system can be configured to not point any beams in the direction of approach and departure paths. This should reduce the amount of 5G power reaching radio altimeter antennas. Just my 0.02.

So after all the fuss this issue seems to have fizzled out, on day 1. My company sent out restrictions for about third of the fleet yesterday, all cancelled this morning.
Reminds me of the Y2K issue, anyone remember Y2K TIBA?

Natflyer wrote:

So after all the fuss this issue seems to have fizzled out, on day 1. My company sent out restrictions for about third of the fleet yesterday, all cancelled this morning.
Reminds me of the Y2K issue, anyone remember Y2K TIBA?

Y2K took all the programmers around the world several years to fix their codes before year 2000 actually hit, and there're still a few minor bugs here and there at the time.
Meanwhile, this time, they only noticed the issue like a few weeks ahead of time, and didn't actually do anything to rectify the issue, but rather simply published a checklist slowly saying what are actually safe.
That it only take them days to publish these information progressively should make one ask why aren't them doing so before the rollout actually start, which would have avoided all the grounding and rescheduling which have happened over the past few days

Revelation wrote:

Boeing12345 wrote:

Thales ERT-530 and -540 is now AMOC approved as well.

For those wondering (like me, who just did some googling), AMOC is "Alternative Method of Compliance" and a FAA document I googled said "The proposed AMOC must include specific conditions that would address the unsafe condition (e.g., by providing information substantiating that certain aircraft or altimeter models are not susceptible to C-Band radio frequency interference)."

In essence, there has been a workaround for the issue on the books all along, just waiting for people to invoke it.

Again, it's not clear what standard FAA is applying when deciding to accept the information that substantiates that the RADALT is not susceptible to C-Band RFI. I presume they aren't setting too high a bar if they can tick the box in just a few day's time.

32andBelow wrote:

Hasn’t the problem the whole time been we don’t know cus we haven’t checked. Which makes this thing so baffling?

It appears you are right. We've had these rounds of chest pounding if not willy waiving, and all that was needed was some clarity on how to file an AMOC and what FAA would or would not approve as Alternative Method of Compliance. Voila, a large percentage of the problem has disappeared.

This is first time in my career that am AMOC has an expiration date. These AMOC's (total of 12) expire on Jan-31 and do not list the same approved airport/runways. So airframe models operating with mixed altimeters have to monitor this incredibly close.

The Airbus with ERT-530 (as one example) did not receive the same relief as other altimeters from an airport/runway standpoint. Some models have different altimeters installed as used/mixed aircraft are bought and inducted. As an example Airbus 319 airframe 1234 is approved for different airport/runway as compared to 319 airframe 4567 because of brand/model installed. Imagine working in dispatch or flight ops and dealing with this?

Boeing12345 wrote:

Revelation wrote:

Boeing12345 wrote:

Thales ERT-530 and -540 is now AMOC approved as well.

For those wondering (like me, who just did some googling), AMOC is "Alternative Method of Compliance" and a FAA document I googled said "The proposed AMOC must include specific conditions that would address the unsafe condition (e.g., by providing information substantiating that certain aircraft or altimeter models are not susceptible to C-Band radio frequency interference)."

In essence, there has been a workaround for the issue on the books all along, just waiting for people to invoke it.

Again, it's not clear what standard FAA is applying when deciding to accept the information that substantiates that the RADALT is not susceptible to C-Band RFI. I presume they aren't setting too high a bar if they can tick the box in just a few day's time.

32andBelow wrote:

Hasn’t the problem the whole time been we don’t know cus we haven’t checked. Which makes this thing so baffling?

It appears you are right. We've had these rounds of chest pounding if not willy waiving, and all that was needed was some clarity on how to file an AMOC and what FAA would or would not approve as Alternative Method of Compliance. Voila, a large percentage of the problem has disappeared.

This is first time in my career that am AMOC has an expiration date. These AMOC's (total of 12) expire on Jan-31 and do not list the same approved airport/runways. So airframe models operating with mixed altimeters have to monitor this incredibly close.

The Airbus with ERT-530 (as one example) did not receive the same relief as other altimeters from an airport/runway standpoint. Some models have different altimeters installed as used/mixed aircraft are bought and inducted. As an example Airbus 319 airframe 1234 is approved for different airport/runway as compared to 319 airframe 4567 because of brand/model installed. Imagine working in dispatch or flight ops and dealing with this?

Are there any units which are all-clear for good, or everything is provisional by now?

Revelation wrote:

Again, it's not clear what standard FAA is applying when deciding to accept the information that substantiates that the RADALT is not susceptible to C-Band RFI. I presume they aren't setting too high a bar if they can tick the box in just a few day's time.

Well at any rate it appears those stone age radio altimeters the manufacturers were too cheap to build to 21st century standards are actually going to work here in the 21st century. It's just too bad the aviation industry and the FAA decided they had to verify that before signing off on it. After all they seem to have been way late to the party so why delay everyone else's fun?

kalvado wrote:

iamlucky13 wrote:

32andBelow wrote:

So to recap.

The band was auctioned off years ago.

The airlines and faa new about this years ago.

Then att and verizon turned their towers on after saying they were going to for months and weeks

And then all the altimeters got approved within 24 hours of that?

Similar claims have been repeated multiple times in this thread. However, when I look for confirmation of the claims, what I find instead is the FCC saying the C-Band auction was less than a year ago:

https://www.fcc.gov/document/fcc-announ ... nd-auction

What was actually happening years ago were the initial discussions over re-allocating part of C-band to mobile wireless telecom. The aviation industry did convince the FCC early on that 4 to 4.2 GHz were too close for the higher power telecom use and would definitely cause interference, but there were still questions about what would happen with telecom in the 3.7 to 4 Ghz range.

Although the aviation industry wasn't itself using the 3.7-4 GHz space previously, the existing licensed uses (satellite transmissions) were very low power and the radar altimeter receivers face away from the satellites, so they did not cause harmful interference with the radar altimeters. Therefore, there had so far been no requirement to update receiver designs to be able to handle higher power transmissions in that adjacent low C-band spectrum, and they were able to be certified to a high design assurance level (A).

The FCC's proposed changes in licensed use altered the operating conditions those certifications were based on, so even with the extra frequency margin, the aviation industry continued its assessment of the interference risks and continued to comment on the FCC notices of proposed rulemaking urging a cautious approach to finalizing the plans to relicense 3.7 - 4 GHz, especially since there were safety implications to trying to move too quickly.

How did the FAA respond to those calls for caution?

They offered the satellite operators $10 billion to significantly speed up vacating their licenses for 3.7 - 4 GHz compared to the previous plan, thereby reducing the time the aviation industry thought they had to investigate and solve the problem down to from 3.5 years down to 1.5 years:

https://docs.fcc.gov/public/attachments ... 4655A1.pdf

Separately, I've been trying to understand some of the technical details being discussed. RF design is well outside my area of expertise, but I think I've been able to piece together a few additional details.

As far as I understand, there's two sides to any interference issue: one is the sensitivity of the radar altimeter receivers to out-of-band-interference (signals not in its intended reception range). The receivers are filtered, but while the common assumption is a band pass filter simply eliminates signals outside of a specified range, in reality it attenuates the signal with increasing effectiveness the further you get from the nominal edge. However, that attenuation might not be total unless you get very far from the passband.

Likewise, transmitters do not simply have a frequency bandwidth exactly at their nominal range. They also have a falloff of decreasing power at progressively further frequencies. They transmit some out-of-band interference. That is, of course, "prohibited" in simple terms, but prohibited here means there is a maximum threshold the transmitter has to comply with.

Some people in this thread have commented about experience with electronics that successfully operates with very small frequency margins. My understanding is that experience with two-way wireless links that operate at similar power levels does not translate well to the conflict we have here between devices of very different power levels.

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

As a final note, I also found a fair amount of technical information on radar altimeters here that some others may find interesting:

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

You're certainly right, more power from the other guy makes it more difficult to deal with. However, keep in mind - low power Bluetooth and microwaves often coexist in the same kitchen, and that is a much higher threshold to clear. Same for GPS receivers in cell environment - GPS signals are way weaker than anything in radalt world, while frequencies are pretty packed as well.
One take-home message from the pdf - many devices do not have crystal oscillators as stable frequency sources, those few which have do not bother to stabilize them. That alone dates designs into a stone age.

My experience with Bluetooth and even WiFi vs. microwaves is that if you are too close, turning the microwave on does cause interference. The distance is only maybe 5 feet, even though the power is on the order of 1000 Watts. Of course, the outside radiated power of the microwave is deliberately as low as practical - the magnetron is in a waveguide that directs the overwhelming majority of that power into the shielded cavity.

iamlucky13 wrote:

kalvado wrote:

iamlucky13 wrote:

Similar claims have been repeated multiple times in this thread. However, when I look for confirmation of the claims, what I find instead is the FCC saying the C-Band auction was less than a year ago:

https://www.fcc.gov/document/fcc-announ ... nd-auction

What was actually happening years ago were the initial discussions over re-allocating part of C-band to mobile wireless telecom. The aviation industry did convince the FCC early on that 4 to 4.2 GHz were too close for the higher power telecom use and would definitely cause interference, but there were still questions about what would happen with telecom in the 3.7 to 4 Ghz range.

Although the aviation industry wasn't itself using the 3.7-4 GHz space previously, the existing licensed uses (satellite transmissions) were very low power and the radar altimeter receivers face away from the satellites, so they did not cause harmful interference with the radar altimeters. Therefore, there had so far been no requirement to update receiver designs to be able to handle higher power transmissions in that adjacent low C-band spectrum, and they were able to be certified to a high design assurance level (A).

The FCC's proposed changes in licensed use altered the operating conditions those certifications were based on, so even with the extra frequency margin, the aviation industry continued its assessment of the interference risks and continued to comment on the FCC notices of proposed rulemaking urging a cautious approach to finalizing the plans to relicense 3.7 - 4 GHz, especially since there were safety implications to trying to move too quickly.

How did the FAA respond to those calls for caution?

They offered the satellite operators $10 billion to significantly speed up vacating their licenses for 3.7 - 4 GHz compared to the previous plan, thereby reducing the time the aviation industry thought they had to investigate and solve the problem down to from 3.5 years down to 1.5 years:

https://docs.fcc.gov/public/attachments ... 4655A1.pdf

Separately, I've been trying to understand some of the technical details being discussed. RF design is well outside my area of expertise, but I think I've been able to piece together a few additional details.

As far as I understand, there's two sides to any interference issue: one is the sensitivity of the radar altimeter receivers to out-of-band-interference (signals not in its intended reception range). The receivers are filtered, but while the common assumption is a band pass filter simply eliminates signals outside of a specified range, in reality it attenuates the signal with increasing effectiveness the further you get from the nominal edge. However, that attenuation might not be total unless you get very far from the passband.

Likewise, transmitters do not simply have a frequency bandwidth exactly at their nominal range. They also have a falloff of decreasing power at progressively further frequencies. They transmit some out-of-band interference. That is, of course, "prohibited" in simple terms, but prohibited here means there is a maximum threshold the transmitter has to comply with.

Some people in this thread have commented about experience with electronics that successfully operates with very small frequency margins. My understanding is that experience with two-way wireless links that operate at similar power levels does not translate well to the conflict we have here between devices of very different power levels.

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

As a final note, I also found a fair amount of technical information on radar altimeters here that some others may find interesting:

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf

You're certainly right, more power from the other guy makes it more difficult to deal with. However, keep in mind - low power Bluetooth and microwaves often coexist in the same kitchen, and that is a much higher threshold to clear. Same for GPS receivers in cell environment - GPS signals are way weaker than anything in radalt world, while frequencies are pretty packed as well.
One take-home message from the pdf - many devices do not have crystal oscillators as stable frequency sources, those few which have do not bother to stabilize them. That alone dates designs into a stone age.

My experience with Bluetooth and even WiFi vs. microwaves is that if you are too close, turning the microwave on does cause interference. The distance is only maybe 5 feet, even though the power is on the order of 1000 Watts. Of course, the outside radiated power of the microwave is deliberately as low as practical - the magnetron is in a waveguide that directs the overwhelming majority of that power into the shielded cavity.

As a matter of fact, in the midst of this discussion I moved my butt out of my armchair and just checked how good my microwave shielding is.
To my surprise, it was meager 25 dB...

hivue wrote:

Revelation wrote:

Again, it's not clear what standard FAA is applying when deciding to accept the information that substantiates that the RADALT is not susceptible to C-Band RFI. I presume they aren't setting too high a bar if they can tick the box in just a few day's time.

Well at any rate it appears those stone age radio altimeters the manufacturers were too cheap to build to 21st century standards are actually going to work here in the 21st century. It's just too bad the aviation industry and the FAA decided they had to verify that before signing off on it. After all they seem to have been way late to the party so why delay everyone else's fun?

There is still no full picture of what is going on. Looks like approvals are provisional, and there are still limitations in place. Oh, and equipment substitutes seem to be the thing.
But nice word and a gun got FAA moving after all.

Some really informative posts on this thread. A few things I'll comment on. Keep in mind I'm an aviation and radio enthusiast and not a professional avionics designer. I realize I am over simplifying things but feel the general concepts should be highlighted. Apologies in advance for anything I got wrong.

iamlucky13 wrote:

In this case, on one hand, we have radar altimeter receivers that have to be sensitive enough that they can detect the non-directional reflected signal from a 1/2 W transmitter.

On the other hand we have cell towers broadcasting in the range of 100W, commonly with a directional beam, so RF level is even more intense, and being received line-of-sight, not reflected. This signal is both transmitted at far higher power, and it experiences far lower attenuation.

Again, this is outside my expertise, but it sounds to me like the huge difference in power levels likely makes faint, stray out-of-band transmission more significant, and weak out-of-band reception more critical. I'd appreciate correction from any electrical engineers, especially if they have RF experience, if I'm off-base here.

Thanks for your very informative post.

The key part of your first sentence is 'reflected' since a RADALT reflects its signal off the ground. Typically, earth is not a great reflector. Some times you get lucky and you're bouncing off a water or something metallic, but most of the time it's vegetation, which is not a good conductor of electricity.

https://en.wikipedia.org/wiki/S_meter has a chart showing the actual receive voltages seen in typical radio applications. The signal voltages are measured in millionths of a volt. In terms of power, https://en.wikipedia.org/wiki/DBm shows the signal powers are measured in picowatts i.e. trillionth of a watt. https://www.britannica.com/technology/radar/Pulse-radar also suggests radar return signals are at the picowatt level. So the output of a RADALT is typically in the half watt level but the return is in the trillionth of a watt level.

The faa.gov/5g chart published in this thread says the US 5G transmit power levels are in the 1.5 kilowatt range. At the risk of over-simplifying things, I don't feel it's hard to see how a 1500 watt direct path signal can override a 0.5 watt signal reflected off the earth. The receivers are designed to block out-of-band signals, but as other posters have stated, it's not a simple problem to solve. The more filtering you do in the front end the more signal you lose and the more distortions you introduce. There is lots of 'prior art' to look at, but each solution ends up being quite unique.

I had a friend who worked on military radars and their problems were often sorting out tiny variations in how various parts were made. They learned an awful lot about screening parts as they arrived before they put them into inventory as spares or for new builds. They still ended up on firefighting drill more often than you would think.

Snowfalcon wrote:

Good points. A few brief comments about the 5G cell towers from someone formerly into spectrum management.

Although the maximum power may be 100W, the system's power control functions always reduce the power on any individual handset connection to the minimum needed to keep the connection alive with an acceptable bit error rate. Which typically is milliwatts or a few watts. Full power is typically used only briefly at connection establishment or when the handset is at the far edge of a large cell. This is a basic function in order to keep the same-channel interference down within the system (i.e. at the next same-channel base station/cell tower).

5G introduces a new "NR" radio interface which includes directional beam forming. This may be a double edged sword, if you think of an approaching aircraft where passengers try to check in to their networks and thereby make beams point towards the aircraft and its radio altimeter antenna. However, the power control still reduces the beams' power to the minimum required. The upside is that the system can be configured to not point any beams in the direction of approach and departure paths. This should reduce the amount of 5G power reaching radio altimeter antennas. Just my 0.02.

Excellent points. These advanced power management and beam forming techniques reduce the nominal power levels but engineers still need to account for the worst case behavior. It makes for a complicated test envelope.

miegapele wrote:

So much drama about impeding doom, and now almost all Airbuses are already approved 24 hours after launch, some Boeing's also are. So, why this was not done year or two ago? FAA continues to look like a joke.

In other words, brinksmanship worked. Necessity is the mother of invention.

It's been pointed out a few times in this thread that the avionics vendors were reluctant to share data to industry groups that were trying to sort things out in advance. Seems getting your product grounded by the regulator changes the terms and conditions on what they will share.

kalvado wrote:

My impression is that, as it is typical these days, FAA set AMOC bar at a tripping hazard level. No information on what exactly is approved in terms of conditions. Are all previously authorized weather within existing minimums - airport (with reduced coverage areas?) - airplane with AMOCed equipment combos still authorized? Could be that approvals are conditional, on "even if it doesn't work, it is not a big deal" basis.
There is basically a total lack of information - both legal and technical, which is unfortunately typical for industry these days. I am not sure what is being hidden - actual trade secrets or lack of competence.

Indeed, there is a feel of "don't look behind the curtain" to all of this.

kalvado wrote:

You're certainly right, more power from the other guy makes it more difficult to deal with. However, keep in mind - low power Bluetooth and microwaves often coexist in the same kitchen, and that is a much higher threshold to clear. Same for GPS receivers in cell environment - GPS signals are way weaker than anything in radalt world, while frequencies are pretty packed as well.

Well said. As I said above, I probably am oversimplifying. Receivers already have a hard job. Nearby high power transmitters make it harder.

kalvado wrote:

One take-home message from the pdf - many devices do not have crystal oscillators as stable frequency sources, those few which have do not bother to stabilize them. That alone dates designs into a stone age.

Right, and when you are working at gigahertz levels (billions of cycles per second), stability needs to be in parts per billion to stay within the band. Most people I know working in this space use temperature compensated crystal oscillators, often using 'GPS disciplining' to get improved stability. Radio hackers like to get temperature compensated crystal oscillators to make GPS disciplined oscillators out of retired previous generation cell tower equipment.

Boeing12345 wrote:

This is first time in my career that am AMOC has an expiration date. These AMOC's (total of 12) expire on Jan-31 and do not list the same approved airport/runways. So airframe models operating with mixed altimeters have to monitor this incredibly close.

This is pretty discouraging. It makes it seem like they just kicked the can down the road yet again. Note how the FAA 'Newsroom' pieces don't mention the expiration dates at all.

Boeing12345 wrote:

The Airbus with ERT-530 (as one example) did not receive the same relief as other altimeters from an airport/runway standpoint. Some models have different altimeters installed as used/mixed aircraft are bought and inducted. As an example Airbus 319 airframe 1234 is approved for different airport/runway as compared to 319 airframe 4567 because of brand/model installed. Imagine working in dispatch or flight ops and dealing with this?

Indeed, a big juggling act to follow.

Natflyer wrote:

So after all the fuss this issue seems to have fizzled out

The beams coming from these 5G "facilities" do a whole lot more than fizzle. Ignore the knock-on consequences, to health and safety, at other's peril.

FAA update:

New approvals allow 78% of U.S. commercial fleet to perform low-visibility landings.

B787, E170/190 new on the approved list.
13 RA types now cleared.

faa.gov/5g

Snowfalcon wrote:

FAA update:

New approvals allow 78% of U.S. commercial fleet to perform low-visibility landings.

B787, E170/190 new on the approved list.
13 RA types now cleared.

faa.gov/5g

Interesting. I know of a few E190 issues in the northeast yesterday. Landing gear warnings getting triggered on approach (basically the RA thought it was close to the ground with no gear extended) while at a few thousand feet not yet configured. Those weren’t within 2nm of an airport, but still distracting on approach nonetheless.

Revelation wrote:

The faa.gov/5g chart published in this thread says the US 5G transmit power levels are in the 1.5 kilowatt range. At the risk of over-simplifying things, I don't feel it's hard to see how a 1500 watt direct path signal can override a 0.5 watt signal reflected off the earth.

Note: Urban 5G base stations are limited to 1584 W/MHz, i. e. at a channel bandwidth of 20 MHz you'd measure a total power output of 31.7 kW right in front of the antenna.
The "true" power output (how much RF power goes into the antenna) is still in the 100 W range thanks to highly directional antennas, which focus all of those 100 W into one specific direction.

JoseSalazar wrote:

Snowfalcon wrote:

FAA update:

New approvals allow 78% of U.S. commercial fleet to perform low-visibility landings.

B787, E170/190 new on the approved list.
13 RA types now cleared.

faa.gov/5g

Interesting. I know of a few E190 issues in the northeast yesterday. Landing gear warnings getting triggered on approach (basically the RA thought it was close to the ground with no gear extended) while at a few thousand feet not yet configured. Those weren’t within 2nm of an airport, but still distracting on approach nonetheless.

Getting into SFO was tough this morning, mostly CJ2, E75, and 320/321ceo were circling for well over an hour+ and diverting to SJC and SMF while 789, 777, 767, 738, 38Ms were able to make it straight in. Our flight was delayed 7.5hrs specifically because CAT III was not an option and we needed 1/2 visibility. We ended up returning to the gate after our EDCT got extended for the 3rd time.

mxaxai wrote:

Note: Urban 5G base stations are limited to 1584 W/MHz, i. e. at a channel bandwidth of 20 MHz you'd measure a total power output of 31.7 kW right in front of the antenna.
The "true" power output (how much RF power goes into the antenna) is still in the 100 W range thanks to highly directional antennas, which focus all of those 100 W into one specific direction.

Not exactly:

"The Wireless Industry’s agenda for 5G is to deploy significantly more data bandwidth and higher data-rates than ever deployed in the entirety of human history.

This ill-advised plan would result in significantly more adverse bio-effects. Even worse, 4G/5G millimeter-wave RF-EMR (~20,000 to 40,000 MHz) is to be beam-formed and sprayed in 15-20 degree-wide beams, a deployment that approaches maser-like, directed-energy weapons (DEW). A maser is a microwave laser or microwave taser."

N212R wrote:

mxaxai wrote:

Note: Urban 5G base stations are limited to 1584 W/MHz, i. e. at a channel bandwidth of 20 MHz you'd measure a total power output of 31.7 kW right in front of the antenna.
The "true" power output (how much RF power goes into the antenna) is still in the 100 W range thanks to highly directional antennas, which focus all of those 100 W into one specific direction.

Not exactly:

"The Wireless Industry’s agenda for 5G is to deploy significantly more data bandwidth and higher data-rates than ever deployed in the entirety of human history.

This ill-advised plan would result in significantly more adverse bio-effects. Even worse, 4G/5G millimeter-wave RF-EMR (~20,000 to 40,000 MHz) is to be beam-formed and sprayed in 15-20 degree-wide beams, a deployment that approaches maser-like, directed-energy weapons (DEW). A maser is a microwave laser or microwave taser."

Looks like someone heard some smart words, but didn't quite got to their meaning. Maybe they had to much of blackbody radiation coming from the nearest star hitting their forehead with adverse results?

32andBelow wrote:

So to recap.

The band was auctioned off years ago.

The airlines and faa new about this years ago.

Then att and verizon turned their towers on after saying they were going to for months and weeks

And then all the altimeters got approved within 24 hours of that?

The auction was in 2020. I’m hearing the wireless operators and FCC didn’t start sharing technical data with the FAA until 2022 (like weeks ago).

N212R wrote:

mxaxai wrote:

Note: Urban 5G base stations are limited to 1584 W/MHz, i. e. at a channel bandwidth of 20 MHz you'd measure a total power output of 31.7 kW right in front of the antenna.
The "true" power output (how much RF power goes into the antenna) is still in the 100 W range thanks to highly directional antennas, which focus all of those 100 W into one specific direction.

Not exactly:

"The Wireless Industry’s agenda for 5G is to deploy significantly more data bandwidth and higher data-rates than ever deployed in the entirety of human history.

This ill-advised plan would result in significantly more adverse bio-effects. Even worse, 4G/5G millimeter-wave RF-EMR (~20,000 to 40,000 MHz) is to be beam-formed and sprayed in 15-20 degree-wide beams, a deployment that approaches maser-like, directed-energy weapons (DEW). A maser is a microwave laser or microwave taser."

That seems to be a quote. So does it have a source?

StinkyPinky wrote:

JoseSalazar wrote:

Snowfalcon wrote:

FAA update:

New approvals allow 78% of U.S. commercial fleet to perform low-visibility landings.

B787, E170/190 new on the approved list.
13 RA types now cleared.

faa.gov/5g

Interesting. I know of a few E190 issues in the northeast yesterday. Landing gear warnings getting triggered on approach (basically the RA thought it was close to the ground with no gear extended) while at a few thousand feet not yet configured. Those weren’t within 2nm of an airport, but still distracting on approach nonetheless.

Getting into SFO was tough this morning, mostly CJ2, E75, and 320/321ceo were circling for well over an hour+ and diverting to SJC and SMF while 789, 777, 767, 738, 38Ms were able to make it straight in. Our flight was delayed 7.5hrs specifically because CAT III was not an option and we needed 1/2 visibility. We ended up returning to the gate after our EDCT got extended for the 3rd time.

With the 5G delay it could just be the airline you were on didn't have the correct equipment on the plane, an MEL that prevented it from using the equipment or a crew that was not certified for CAT III. I've seen all 3 things happen in the past.

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

casinterest wrote:

c933103 wrote:

casinterest wrote:

CBand for the Wireless companies is 3.7GHz to ~4Ghz
The radar altimeters on the planes are at 4.2 to 4.4 Ghz.

Don't these altimeters understand when the frequency coming back to them is not the one they are sending out?

Or is the Risk, that they can't control the frequency between the plane and the Ground and interference may occur?


Why not a sensible solution that the Cell companies around an airport use lower band frequencies (3.7-3.8)around the airport? The signal should stay out of the 4.2 to 4.4 range, even with 10-20% tolerance issues.

The auction was done in piece, every 20MHz. Like 3.7-2.72GHz is one segment, 3.72-3.74 is another, and all the way to 3.96-3.98, with the last slice of 3.98-4GHz being reserved exactly for the guarding purpose to separate from other bands, and then there are also another 200MHz between these and the Altimeter frequency.
Modern altimeters can distinguish these different frequencies, but some of the older ones cannot.
3.7-3.8GHz is still part of the FAA complain against the entire band, and limiting operation to this would nullifying two-third of the bidded mobile service capacity which operators spent tons of money to acquire, in addition to they might not be the same company who won the auction of higher parts of the band depending on location as different carriers bid different part of the spectrum and there are also some smaller companies who won a few pieces of these frequencies in some limited geographic area according to my understanding. Limiting operation to lower frequency band would mean all the investment and equipment paid by those who bidded in higher band will be completely wasted, for no good reason since even the closest band is still 220MHz away from the altimeter frequency, when those mobile communication each of them only use 20MHz

The issue of course is that no one vetted the old technology that claimed the 4.2 to 4.4 range. That is where the issue lies, but it is also least likely to be remedied anytime soon. The FCC sold the licenses, and the FAA failed to act expediently on an issue that has certified parts operating outside the licensed and advertised range.

"that no one vetted the old technology that claimed the 4.2 to 4.4 range" they are not emitting out of band signal so it does not cause concern to other party. Hence the FCC didn't complain to aircraft with relevant radio altimeters. The problem is they might receive signal from out of the band. And since it is the signal they receive, the problem lies within the equipment ithemselves, and when it's related to safety, it'd be the one oversighting safety of such equipment to be responsible for them not being unsafe.

N212R wrote:

mxaxai wrote:

Note: Urban 5G base stations are limited to 1584 W/MHz, i. e. at a channel bandwidth of 20 MHz you'd measure a total power output of 31.7 kW right in front of the antenna.
The "true" power output (how much RF power goes into the antenna) is still in the 100 W range thanks to highly directional antennas, which focus all of those 100 W into one specific direction.

Not exactly:

"The Wireless Industry’s agenda for 5G is to deploy significantly more data bandwidth and higher data-rates than ever deployed in the entirety of human history.

This ill-advised plan would result in significantly more adverse bio-effects. Even worse, 4G/5G millimeter-wave RF-EMR (~20,000 to 40,000 MHz) is to be beam-formed and sprayed in 15-20 degree-wide beams, a deployment that approaches maser-like, directed-energy weapons (DEW). A maser is a microwave laser or microwave taser."

The "RF-EMR (~20,000 to 40,000 MHz)" are, in other words, 20-40 GHz.
We are not talking about 20-40 GHz frequency band in this thread. We are talking about 3.7-4 GHz and 4.2-4.4 GHz

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

You have to keep in mind that the FAA had a number of other high priority items to address such as the whole MAX fiasco, coming up with a new phrasing for "Notice to Airmen" that is acceptable in today's world but still acronyms out to "NOTAM" to maintain continuity in terminology, etc.

hivue wrote:

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

You have to keep in mind that the FAA had a number of other high priority items to address such as the whole MAX fiasco, coming up with a new phrasing for "Notice to Airmen" that is acceptable in today's world but still acronyms out to "NOTAM" to maintain continuity in terminology, etc.

Well that really builds confidence in the FAA's ability to do their job. First they failed with the "whole MAX fiasco", then they failed with a syntax issue, and now they failed to manage a years old known technology transition. They announced a potential shutdown of all civil aviation in the US due to an immediate danger of planes crash landing, and then less than a week later they say, "Nevermind". This was clearly a pissing match between the FCC and FAA, but it's the FAA that appears to be the big loser in credibility.

hivue wrote:

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

You have to keep in mind that the FAA had a number of other high priority items to address such as the whole MAX fiasco, coming up with a new phrasing for "Notice to Airmen" that is acceptable in today's world but still acronyms out to "NOTAM" to maintain continuity in terminology, etc.

FAA decided in early January they won't request carriers to further defer 5G entry into service in those frequency band after the deferral from Jan 5 to Jan 19.
That the equipment list only published after Jan 19 but still just within few days of the date mean that, either
a.) FAA wrongly estimated the time needed for them to finish all the paperworks, and what they predicted to be able to complete within 2 weeks time actually need 2.5 weeks to complete. In this case they should have requested another week of extension, which I don't think carriers would be too oppose to the idea as it's going to reduce negative publicity against their new technology by quite a bit. Or,
b.) FAA didn't really spent the two weeks doing much things, and only hurriedly publish the necessary directive and approval list in the hours after the 5G actually entered into service. Or,
c.) Someone in FAA is unpleased with the situation and just want to show to the other party this is what would happen if you don't listen to us

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

We are being told in this thread that the clearance is only temporary.

hivue wrote:

You have to keep in mind that the FAA had a number of other high priority items to address such as the whole MAX fiasco, coming up with a new phrasing for "Notice to Airmen" that is acceptable in today's world but still acronyms out to "NOTAM" to maintain continuity in terminology, etc.

Funny how easily boomers are triggered.

Revelation wrote:

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

We are being told in this thread that the clearance is only temporary.

As some wise man say,

Revelation wrote:

Reminds me of a saying: there's nothing as permanent as a temporary tax!

kalvado wrote:

Revelation wrote:

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

We are being told in this thread that the clearance is only temporary.

As some wise man say,

Revelation wrote:

Reminds me of a saying: there's nothing as permanent as a temporary tax!

It really feels as if the rules are being made up as we go. I really hope this does not end up with an aviation disaster. It really feels like FAA is just rubber stamping paperwork to get through the current crisis.

Revelation wrote:

kalvado wrote:

Revelation wrote:

We are being told in this thread that the clearance is only temporary.

As some wise man say,

Revelation wrote:

Reminds me of a saying: there's nothing as permanent as a temporary tax!

It really feels as if the rules are being made up as we go. I really hope this does not end up with an aviation disaster. It really feels like FAA is just rubber stamping paperwork to get through the current crisis.

My thoughts exactly. While I enjoy u/AdmiralCloudberg's write ups on Reddit, I hope this doesn't become an eventual write up by him.

Could passive reflectors in the last ten miles of a flight path be constructed to help with this. Also, could those reflectors be tuned and aimed for maximum reflection back to the plane. Us small boat operators are often told that passive radar reflectors can ensure we are seen.

frmrCapCadet wrote:

Could passive reflectors in the last ten miles of a flight path be constructed to help with this. Also, could those reflectors be tuned and aimed for maximum reflection back to the plane. Us small boat operators are often told that passive radar reflectors can ensure we are seen.

I don't think so. It's one thing to redirect enough radar energy back to a receiver tuned to receive it vs redirect all radar energy away from a given area. As mentioned earlier in the thread, 5G transmitters can do "beam steering" and in theory they could be programmed to not beam energy towards airports, but the telcom industry wants to move forward without restriction and FAA wasn't proactive enough to stand in the way of that.

frmrCapCadet wrote:

Could passive reflectors in the last ten miles of a flight path be constructed to help with this. Also, could those reflectors be tuned and aimed for maximum reflection back to the plane. Us small boat operators are often told that passive radar reflectors can ensure we are seen.

Interesting idea. But my understanding is that the great benefit of the radio altimeter is that it works independently of any external supporting means on the ground. It is therefore equally useful as a ground proximity warning device above an airport approach path as everywhere else.

The small boat radar reflector you refer to is more of a vessel-to-vessel collision warning aid. This is a different function of radar, which in civil airplanes is performed by the TCAS system.

Revelation wrote:

frmrCapCadet wrote:

Could passive reflectors in the last ten miles of a flight path be constructed to help with this. Also, could those reflectors be tuned and aimed for maximum reflection back to the plane. Us small boat operators are often told that passive radar reflectors can ensure we are seen.

I don't think so. It's one thing to redirect enough radar energy back to a receiver tuned to receive it vs redirect all radar energy away from a given area. As mentioned earlier in the thread, 5G transmitters can do "beam steering" and in theory they could be programmed to not beam energy towards airports, but the telcom industry wants to move forward without restriction and FAA wasn't proactive enough to stand in the way of that.

I assume idea is to have radar target on the ground - similar to retroreflectors on bicycles or traffic signs. Without doing math, my impression it would be much harder and less efficient than it sounds.

And an interesting statement about effect on approved operations in this thread:
viewtopic.php?f=3&t=1469507

KCaviator wrote:

Here's a little more info for you since you're questioning my answer:

The Embraer 175 has a logic that inhibits certain EICAS messages in different phases of flight. These are known as K-codes. One of the phases is from 80 knots to 400 feet AGL during takeoff. This is obviously a very critical phase of flight. Many EICAS messages are inhibited during this time so that crews are not distracted by something that is relatively unimportant for that critical phase of flight. This is where 5G comes into play. Embraer has determined that 5G could cause Radio Altimeter interference, therefore making the aircraft think it's above 400 feet AGL and thus allowing unimportant and possibly irrelevant EICAS messages. One example would be a brake failure at, say, 100 knots. This scenario typically would not be presented to the pilots until 400 feet AGL because of the K-code inhibiting. If the RAs are malfunctioning with 5G, this message could appear during the takeoff roll. Now you have a flight crew aborting the takeoff with impaired/inoperative brakes. Hence, now there's a takeoff weight penalty that accounts for this worst-case scenario. EYW is the most affected with possibly 4200 lb MRTW reductions. A wet runway further exemplifies the issue.

Heard all new AMOC's will be issued early next week regarding the deadline of Jan-31. The language stated "updated expiration date" so sounds like just additional time and not permanent. When I see them next week, I'll post an update.

Revelation wrote:

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

We are being told in this thread that the clearance is only temporary.

Somebody please explain to me how hardware approval can be safe enough for a temporary time period, but not safe enough for an indefinite time period.

This reminds me of how Boeing thought the MAX would be safe enough after crash #1 until their software patches would be available.

Chemist wrote:

Revelation wrote:

Chemist wrote:

So nothing happened for over a year and suddenly in the space of a few days a high fraction of the hardware is cleared?
What took so long to get going, guvmnt?

We are being told in this thread that the clearance is only temporary.

Somebody please explain to me how hardware approval can be safe enough for a temporary time period, but not safe enough for an indefinite time period.

This reminds me of how Boeing thought the MAX would be safe enough after crash #1 until their software patches would be available.

Risk management. if they estimate <0.01 crash over the month for the fleet, then it is not too bad. If that is allowed to hold for 100 months (8.5 years) , then it is almost a certain crash and a no-go.

This seems very drawn out and complicated for something that should be able to be fixed with a simple band pass filter on the receiver.