Because there is no evidence of any interference. Boeing and Airbus are requesting something without showing any evidence, which could have been easily detected in a test environment.

Why is Airbus randomly asking for that in the USA and not e.g. in Europe?

Europe didn't assign 3.8-3.98GHz band to 5G - outside of limited deployments in UK, the allocation stops at 3.8GHz and the next band starts way further than 200MHz away from end of aviation bands.

The initial deployment of C-Band in the US is from 3.7 to 3.8 GHz leaving a nearly 400 MHz guard band. Anything above 3.8 GHz won't be deployed for nearly two years, after the incumbent satellite operators clear the spectrum.

Their views aren't even that logical.

You already need multiple radar altimeters on ONE plane much closer physically and spectrum wise than 5G. In busy airports you already have multiple altimeters operating again closely physically.

Anyways, even if there is interference, it's actually boeing that should fix their systems to operate within their assigned band (ie, operate in the middle of the band, and reject signals outside of band). This is radio 101 stuff.

Only one radar altimeter is generally operational at a time (transmitting), due to high bandwidth involved, and latest ICAO working group reports are "we don't know yet if it's safe with current equipment, retrofitting will take years as they can't even start designing new models till interference data is available, and that countries are implementing temporary mitigations in 5G base stations"

That's where we find how technically incompetent ICAO is I suppose?

Something that has been a decade in the making, they haven't been able to conduct basic tests on. I'm a lay person, but can easily think of basic tests that would help resolve this question.

"On a large aircraft two or three altimeter systems are employed and these systems could utilize a frequency offset of 5 MHz to 10 MHz."

Something is rotten with the regulators.

Radio altimeters have bandwidth as high as 170MHz, and a lot of work goes into ensuring other devices in 4.2-4.4 band do not interfere with them.

The fact that certain radio systems can utilize low bandwidth does not mean every system is like them.

Are you sure? That's an almost impossibly high receive bandwidth for an older type of equipment I would think.

I've seen bandwidth ranges of 50Hz to 300Hz (that's Hz not KHz or MHz). This is swept or chirped over a frequency (bigger is better for that - so 200Mhz good and they'd probably want more).

But in terms of a guard, you should be able to guard much tighter than 200Mhz - that's what I'm not understanding - but haven't looked at it closely.

Frequency Modulated Continuous Wave radars used for most civilian radar altimeters sweep most of 200 MHz bandwidth, largest known case is 196 MHz. Transmit power ranges between 0.1 to 100W.[1]

As another commenter mentioned, making a broadband filter for such wide bandwidth is... problematic, and it's one of those devices where you might want to use fixed function rather than SDR.

[1] https://www.icao.int/NACC/Documents/Meetings/2018/RPG/RPGITU...

The sibling comments here are also correct of course but keep in mind that 5G, excluding stuff like mmWave, does not prescribe any particular frequency band to use and can work on just about any. Regulators will find some slice of free frequency space somewhere between roughly 1 GHz to 5 GHz and auction it off and then carriers and device manufacturers will make 5G run in that band. The iPhone 13 for example can use literally 30 different 5G bands on the US models.

Probably because there isn't any problem. Though it could also be that 5G in the US is meant to use some different channels / frequencies than elsewhere, as was done in older wireless standards.

Most countries simply don't allow the frequencies FCC wants to approve.

Nearly 40 countries have already adopted rules and deployed hundreds of thousands of 5G base stations in the C-Band at similar frequencies and similar power levels—and in some instances, at closer proximity to aviation operations—than 5G will be in the U.S. None of these countries has reported any harmful interference with aviation equipment from these commercial deployments, as the Federal Aviation Administration recently confirmed.[0]

[0] https://ecfsapi.fcc.gov/file/1103192305940/211103%20CTIA%20E...

The very nice weasel wording used tries to make it sound like 40 countries approved above 3.8GHz, but the further paragraphs explain that only japan did so, without going into much detail other than the low guard band.

The FAA complaint is about 3.8-3.98GHz, and all other examples involve no frequency allocations above 3.8GHz

Absolutely zero weasel wording. The initial deployment of C-Band in the US is 100 MHz of spectrum from 3.7 to 3.8 GHz. The remainder of the auctioned C-Band from 3.8 to 3.98 cannot be deployed until the incumbent satellite operators clear the band on or before December 2023. For 2 years there will be a 400MHz guard band.