[zachberger]

> The problem is that radio altimeters are pretty old

Interestingly the 737-200 is excluded from this airworthiness directive. 737-200s are the oldest, still-operating members of the 737 family.

[bastardoperator]

Total noob question, why isn't Boeing building/buying new radio altimeters that can filter better? Is it a money thing, a technology thing, maybe both?

[p_l]

It's not just Boeing. Boeing orders certified radar altimeter devices for their configurations, and then certifies the whole assembly of it on a plane. The whole technology of radar altimeters makes it particularly hard to filter out 5G signals at 3.98GHz.

As part of trying to keep flying safe, both attempts to limit sources of interference (i.e. 5G transmitters) and checks on existing hardware (and thus whether it needs to be replaced) are done in parallel. Outside of USA, everyone agreed on various mitigations to limit impact to radar altimeters especially as full impact of C-band 5G is still work in progress.

[cyberpunk]

Certification I guess. It probably takes 2 years (at least) and an insane amount of money to change any component on an already certified plane.

[altairprime]

While not a direct answer, see also: “Boeing engineers lost controls of the company” (2019) https://news.ycombinator.com/item?id=21304277