just put some 4150 4450 Mhz band pass on altimeter receiver and antenna path , and a big notch filter betwen 5g TX and its radiator

Remember, the altimeter works like a radar. The altimeter transmitter has to comply with spectral mask requirements as well and the altimeter receiver bandwidth has to be wide enough to receive weak reflections. So, it’s necessary for the receiver bandwidth to be very wide. It’s not a “lousy front end receiver”, it’s a necessary front end receiver. You can’t expect the airline industry to spend a fortune to retrofit proven safety equipment because the FCC and Telecom industry bent the rules to make money.

If this discussion really does turn political, comments will be held back from publication or be subjected to editing. We haven’t reached that point yet, but we’re watching.

Just a reminder, let’s keep this discussion technical and not let it deteriorate into anything even slightly political. There are plenty of other sites for political discussions.

Case in point, “Wireless network operators and aviation authorities routinely trade barbs over spectrum, but this latest snafu takes things to a whole new level. The Federal Communications Commission (FCC), Federal Aviation Administration (FAA), and Department of Transportation have fantastically failed the people they are charged to serve,” wrote Matt Kepko on sdxCentral.
https://www.sdxcentral.com/articles/opinion-editorial/op-ed-mid-band-5g-meets-american-incompetence/2022/01/

Per the 3GPP technical specifications, 5G transmitters are attenuated at -13dBm per 0.2 MHz outside their band. Given that until 2024 the guard band between 5G and radio altimeters is 400 MHz, the possibility of interference is nil, even with such a lousy front end receiver at in Fig. 2.

So, your view of an alleged co-channel interference issue, where an astounding, unprecedented, unnecessary and spectrum-wasteful 400 MHz guard band exists between two non-competing radio spectrum services, is that our domestic government bureaucracy isn’t large enough and there exists too little regulation? Obviously your position is from a political and not RF engineering one.

Figure 2 is just showing a “typical” receiver front-end filter response and that’s not regulated. Transmitters are regulated, but poorly enforced and that’s what happened here. There are National and International spectral mask requirements on transmitters to limit adjacent channel interference. An example can be seen in the NTIA Annex J where (for some applications) transmitters require no attenuation within the modulation bandwidth (necessary bandwidth), but out of band rolls off at -40 dBsd to -60dBsd within the allocated channel.

That’s not the message I get from Figure 2.