FYI: nm = nautical miles, not nanometers.

I don't know how long that failure mode has been in place or if this is relevant, but it makes me think of analogous times I've encountered similar:

When automated systems are first put in place, for something high risk, "just shut down if you see something that may be an error" is a totally reasonable plan. After all, literally yesterday they were all functioning without the automated system, if it doesn't seem to be working right better switch back to the manual process we were all using yesterday, instead of risk a catastrophe.

In that situation, switching back to yesterday's workflow is something that won't interrupt much.

A couple decades -- or honestly even just a couple years -- later, that same fault system, left in place without much consideration because it rarely is triggered -- is itself catastrophic, switching back to a rarely used and much more inefficient manual process is extremely disruptive, and even itself raises the risk of catastrophic mistakes.

The general engineering challenge, is how we deal with little-used little-seen functionality (definitely thinking of fault-handling, but there may be other cases) that is totally reasonable when put in place, but has not aged well, and nobody has noticed or realized it, and even if they did it might be hard to convince anyone it's a priority to improve, and the longer you wait the more expensive.

Good news: the system successfully detected an error and didn't send bad data to air traffic controllers.

Bad News: the system can't recover from an error in an individual flight plan, bringing the whole system down with it (along with the backup system since it was running the same code).

You know there's a software engineer somewhere that saw this as a potential problem, brought up a solution, and had that solution rejected because handling it would add 40 hours of work to a project.

There's been some prior discussion on this over the past year, here are a few I found (selected based on comment count, haven't re-read the discussions yet):

From the day of:

https://news.ycombinator.com/item?id=37292406 - 33 points by woodylondon on Aug 28, 2023 (23 comments)

Discussions after:

https://news.ycombinator.com/item?id=37401864 - 22 points by bigjump on Sept 6, 2023 (19 comments)

https://news.ycombinator.com/item?id=37402766 - 24 points by orobinson on Sept 6, 2023 (20 comments)

https://news.ycombinator.com/item?id=37430384 - 34 points by simonjgreen on Sept 8, 2023 (68 comments)