Magitek Operator

[dairius_chi]

Think of it like the Synthesist Archetype for the Summoner class in Pathfinder, you stat out the Automaton as if it was its own creature (with no Int, Wis, or Cha), following the table as a standard Engineer would, and when piloting it you use its stats and have its HP pool as 'temporary hit points' to symbolize how much of a beating the Magitek can take.

So yes, whatever its AC would be you use while piloting it, but it wouldn't benefit from any armor or magic items you're wearing like a Ring of Protection, you'd have to slot Protect Materia into its armor for something like that.