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?
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.
> "Move fast and break things" doesn't work well with aircraft.
Sure, but that didn’t seem to stop faulty lithium batteries on the 787 or MCAS on the 737-MAX. If only Boeing would learn the lesson, maybe we wouldn’t have these messes.
As has been pointed out several times already, this is not a Boeing problem. It affects practically every major aircraft manufacturer.
If anything, Boeing has been very proactive about identifying the affected equipment well before any accidents happen. This is precisely what they should be doing.