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FAA: Airlines must retrofit faulty altimeters “as soon as possible”

The Federal Aviation Administration says it finally has a plan for the industry to replace or retrofit airplane altimeters that can't filter out transmissions from outside their allotted frequencies. The altimeter problem has prevented AT&T and Verizon from fully deploying 5G on the C-Band spectrum licenses the wireless carriers purchased for a combined $69 billion. The FAA was urging airlines to retrofit or replace altimeters in recent months and now says it has finalized a plan. An… ( More...

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Billy Koskie 9
If there is no manufacturers building approved filters, how are the airlines supposed to install said filters? Does anyone know if this is correct?
tony badzioch 5
A few years ago the GPS industry had the same problem. One man then designed a proper filter for his GPS receivers while the rest of the industry continued to whine about the transmitter being too close to their state of the art designs. He then went and gave out his filter's design info for free.
Jim Allen 1
They’re being built overseas.
Jesse Carroll 1
So what else is new!
sparkie624 1
Ain't that the Truth... We have been retrofitting planes for Decades! Look at GA with the Avionics Upgrades that Rival many Airliners.
amacnabb 22
As a licensed amateur radio operator and radio/electronics enthusiast for 40+ years (and from reading much information about this issue), it sounds to me like it IS, in fact, the aircraft equipment that is lacking, not the cell-phone carriers.

This all seems to be clear case of the aircraft using older (?), or perhaps technologically obsolete (or at least deficient) equipment designs. If the altimeter receivers have such poor band/frequency selectivity and lack of out-of-band dynamic range, that they are (or will be) interfered with by a signal from outside of their specific operating frequencies, then they are the problem. If the "offending" transmitter(s) (in this case, the 5G cell-phone signals) are within their operating parameters, then it is not the responsibility of the transmitter to be corrected, but rather the [poor] receiver to be corrected.

As a radio operator, if I'm transmitting on a legally-assigned frequency, and my transmission characteristics are within the "legal" and acceptable operating parameters (for modulation bandwidth, carrier power, etc.), and yet my transmissions are somehow interfering with your equipment (which may have poor selectivity and lack of dynamic range), I am not at fault, YOUR equipment is. Therefore, it is not my responsibility to correct your faulty equipment.

While it seems like the FCC (and FAA) should have perhaps been more "in-the-loop" early-on, and explored the possibilities of any cross-band interoperability issues beforehand, the FCC cannot control the technical issues of the poor receiving equipment; receivers don't create interference, they only "hear" it. The FCC can only allocate band assignment and usage, and regulate the TRANSMITTERS used on those bands. In addition, the FAA probably created (or had a hand in creating) the spec's for the altimeter receivers, so they should have also known there might be a conflict.

Imagine if the situation were reversed, and the 5G cell-phone carriers were experiencing some interference from the aviation altimeter transmitters. Would the altimeter transmitter manufacturers be required to pay for "fixing" (i.e., "improving") the 5G cell receivers? Of course not! That said, however, if the altimeter transmitters were operating in such a way (out-of-band spurious signals, etc.) as to be CAUSING the 5G interference, then it would be on them to correct their equipment.

Lastly, since the new 5G cell equipment is most likely the latest, greatest, state-of-the-art radio gear, it is VERY unlikely that their transmitters would be operating, in any way, outside of their very tight and regulated specifications.
I too am a licensed amateur and I have had occasion to buy a neighbor a filter for his TV and explained to him that it was not my transmitter but his receiver. The filter worked as it was supposed to and I never again had any complaints about interference.
Dan Boss 5
The problem is not as most of the commenters have postulated. No offense to amateur radio, or similar engineers. The problem is twofold:

1) FCC was made aware of the interference issue with RA (Radio Altimeters), but they went ahead and sold frequencies too close to the RA bands. Europe did not do this and left a wider safety margin.
2) Radio Altimeters are supremely integral to airliner safety - being tied into a half dozen primary and critical avionics safety systems. But the biggest issue, is to get a new piece of such critical avionics safety related hardware through the testing and approval process - can take a decade or more! It does not matter if such and such technology is off the shelf to upgrade existing RA equipment - the approval for the modifications or entirely new RA devices - will take a decade to get tested and approved. Not because of bureaucratic bull chips, but because of rigorou8 safety regime specifications and redundancy issues.

So all the pin heads arguing who should pay are missing the real problems - FCC should not have sold frequency bands that are part of present safety margins. So either they should pay or disallow the freq bands they erroneously sold, and refund the cell carriers for revoking the appropriate bands.

And then allow the proper lead time to get all RA equipment upgraded!
sparkie624 3
The Carriers were pushing the FCC to begin with and money talked and lined pockets at the FCC... The FCC ignored the Warnings.. that is why I say the Cell Phone Companies should foot the bill because they alone are the ones who stated this entire episode. Very Simple Solution... Get Rid of all the existing 5G that they did not test properly and say "So Long Charlie, Better Luck Next time!" but we know that won't happen!
Jim Allen 1
Boeing gave them the specs. If Boeing screwed up.. oh well.
victorbravo77 3
I thought FCC requirement is for a proposed new service to not interfere with existing services, not the other way around. Why is the burden for avoiding interferenced put on the FAA and airlines on not on AT&T and Verizon?
Michael Hawke 16
Because the burden is on the altimeter manufacturer to build a device that operates in its given frequency band. The original design should have included a filter in the original design
sparkie624 -7
Radio Altimeters were around decades before the first Cell Phone. It is the Cell Phone Companies problem to fix and it should all be on their shoulders. This is kind of like you moving in to a Neighborhood and a new neighbor comes in next door and Builds a fence on your property and that is what they are doing.
CathyDrzyzgula 10
No, it is like a new neighbor moves in and builds a fence on their own property and the old neighbor is upset because they used to walk their dog there.
Jim Allen 12
Maybe you need to update a 40 year old radio altimeter. Things change.
Steve Strong 16
Michael Hawke is correct from an engineering point of view. Sparkie624, your analogy is factually incorrect as to what is happening here. To work with your analogy, it's actually like your new neighbor builds a fence on their property and it's 20 feet away from your property, but you complain that you can see their fence even though it's no where near your property.

The FCC requires a specific spectral mask such that there is very limited emission outside your allocated spectrum. It's man made so you can't go from 100% to 0% in an instant but the amount is highly reduced and goes to 0 pretty quickly. There is more than sufficient guard band between the 2 uses. That's the spectrum in between to account for the inability to go to 0 in an instant. The problem lies with the RA's and while I'm not sure of the history, likely the FAA and their requirements to be approved to put it in an airplane.

If you build a defective product but you got lucky and no one noticed until years later, that doesn't mean the person that noticed the defect is wrong, it's still a defective product.
Follow the money...
JeffDickinson 1
At the end of the day and all bitching aside, the airlines will upgrade their radio altimeters and 5G will be deployed. The only thing that will change is our ticket prices to fly to pay for the upgrades. Because in the end, it's always the user paying for all of the changes. I personally think the airlines should file a class action lawsuit again the cell companies for causing the issue. I think the cell phone companies didn't properly test the frequency bands as required by the FCC for the license approval and the FCC wasn't knowledgeable enough to know it would affect radio altimeters build before 1990. That system has been on aircraft since the 60's. Same basic system was used on Apollo to land on the moon.
Jim Allen 2
Yes, the FCC should’ve known. There’s probably $69 billion reasons the FCC didn’t bother to consult the FAA. Keep in mind, this is the same FCC that disavowed Net Neutrality to give carriers the right to favor certain content over others. Why? To fund internet expansion in rural locations.. 😂
Anthony Fiti 1
The FCC did consult with the FAA. There were filings in the FCC docket regarding opinions from the aviation industry.

By Boeings own words, that a 220MHz guard band should be enough for RAs. That that the FCC accepted and it turns out the aircraft manufacturers were wrong.
sparkie624 -1
Why is the FAA not failing on side of Safety during all of this... They need the bigger filter and the Cell Phone companies need to pay for the parts!
Michael Hawke 11
Why would cell companies have to pay. The problem is that the manufacturers of the altimeters did not design in or build filters in the units from the start. It is their design issue not the cell phone companies.
sparkie624 0
Be cause they are the ones causing the problem... Why should they not!
Jim Allen 6
That’s kind of like saying we shouldn’t build bridges because it puts ferry companies out of business. Is it a screwup? Completely. Aircraft manufacturers love less oversight when it benefits them but cry when it costs them money. Do I feel bad for the GA pilot that needs to replace their altimeter? Of course.
Steve Strong 4
I'd love to get a true history of the design requirements for the RA's as well. I don't know if the manufacturers got sloppy to cut costs on what was already probably crazy expensive because of regulation, or if what often happens, the regulators create the requirements and the manufacturers rarely go beyond because it tends to attract unwanted attention.
Steve Strong 8
I hopefully addressed this above for you, but the cell phone companies are NOT causing the problem. They simply made a product that exposed the problems in the radio altimeters. There is really nothing the cell phone companies could have done different. They are in the right from a technical point of view. You are effectively saying because the RA's are defective, no one should use massive amounts of spectrum anywhere near the RA's. Back to your previous analogy, it's like you are saying because you built your house on your property years before your neighbors and you liked the view, now you don't want any of your neighbors to be able to build houses on their property because it'll ruin your view.
chugheset -1
I think the title of this article is a bit disingenuous suggesting the existing altimeters are "faulty". They have seemed to work perfectly fine until ATT and Verizon came along.
James Werner 7
That's a bit like saying that your car worked perfectly until a State Trooper came anong and gave you a ticket. No ody noticed the faulty altimeters until someone came along and wanted to use a lane that the instrument is blocking. More to the point, the cell phone companies paid for that bandwidth and the alitimeter operators didn't.
chugheset 1
I guess it depends upon the nature of the ticket. If he cited me because my car is blue and since the police recently started wearing sunglasses that were incapable of seeing that color thereby rendering my car invisible, then yeah, I guess I can see your point. As far as payment for the bandwidth, the radio altimeter was patented in 1924 ten years before the FCC was even in existence. I'd say it has seniority.
gorbush -1
Strange thing that this is not an issue in Europe where 3.8GHz 5G is common place.

I rather suspect that it is a problem with "ass security" where device has to get certification that it is able to work in enviroment where 3.8GHz cellurar band is used.
sparkie624 1
Different type of Modulation... Different effects, different ways of broadcasting. That is why our Cell phones do not normally function correctly in Europe or other places around the world. Comparing apples and Oragnges.
gorbush 5
Problem with interoperability of cellphones between countries comes mostly from different frequency band. In USA case there was also prevalent use of CDMA rather than GSM TDM. From 4G era that came to past. Right now 5G in USA is exactly the same as 5G in Europe. With minor frequency band differences (n77 vs n78).
gorbush 8
After some more digging I found out that Verizon, AT&T and T-Mobile got frequency bands up to 3.98GHz. In Europe that is only up to 3.8GHz. That could make quite a difference. :(
Even so 120MHz band gap should be more than enough for radio device safety. In radio communication common practice is just 20MHz gap.
Verizon, AT&T and T-mobile should be paying for the radio altimeter upgrades. The FCC should have known that 5G would be to close to the C band altimeter. The government messed up. The FCC and the FAA both dropped the ball on this.
David Hasse 6
Either the 5G telecom broadcasts are staying within the frequencies they are paying for or they aren't. If the RF altimeters do not have the ability to discriminate and filter out frequencies not in the band they are allocated it is not a telecom problem. Frequency lock is more efficient in the first place and has been around since FM radio, it isn't exactly a new concept.
Jim Allen -4
Shameless MF’ers- if it’s Boeing, lax oversight is OK.
Airlines for America, a trade group that represents the major US airlines, is not so happy. "We have serious concerns that the Federal Aviation Administration (FAA) has placed the burden on the aviation industry to act in a way that would previously be considered, by the FAA itself, to be reckless in the context of design changes to safety-critical avionics," the group told FAA Acting Administrator Billy Nolen in a letter on Friday.


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