[bibabaloo]

Planes have just as much spaghetti code as anything else, the only difference is that it's extremely well tested (functionally) and verified spaghetti code.

[cudder]

It's not hard to imagine there would be even more than in less verified fields, since if you try to clean it up you need to verify it again too.

[mr_toad]

From talking to someone in the industry TDD seems to be a popular methodology.