Tracer ammunition in aerial weapons?

[Johnny .45]

I think you're right about flexible guns almost always using tracer ammo, especially ones without any gyroscopic sight...otherwise it'd be almost impossible to hit a target.
And I think that "Pilot" is also right about particular units being the ones who decided whether to use tracer ammo. I just read something the other day (although I can't remember WHERE I read it) about how generally, tracers in fixed guns "served little purpose other than to alert the enemy that he was under attack". I'll have to figure out where I read that quote...my memory can be pretty terrible sometimes!