All kinds of maitenance over systems that can't fail. Basically you sit on your ass 24/7 while getting high check and only from time to time repair
actually replace complete modules of a thing.
Fuckton of money, lots of boredom, a lot of time to read books or do other stuff. Oh wait, it's less of an engineering job and more of a specialized trade, but whatever.
Another way to jew system out of money is being auditor or a guy that gives some certification like electromagnetic compatibility.