Well, there doesn't seem to be a specific skill for bombing (unless I'm completely missing it), so I'd think it would simply be a Natural Aptitude for Gunnery/Aerospace rather than bombing specifically.
Of course, if you wanted the character to be better at bombing specifically, then you could give the character a Specialty of Bombing for his Gunnery/Aerospace skill. That would give the character an additional +1 when bombing, at the cost of having a -1 for all other Gunnery/Aerospace skill checks.
Presumably you could even apply both of them. Give yourself a Natural Aptitude for Gunnery/Aerospace, and a specialization in Bombing, then you'd be rolling 3d6 and have an additional +1 for bombing :)
Of course, if its a NPC and you're the GM, you can pretty much do whatever you want...
