Autothrusters:

When defending beyond range 2 OR outside of the attacker's firing arc change blank result to an evade result. OK first part is easy enough it's the second part after the "OR" that I don't understand. If your ship is outside of the attacker's firing arc how can it fire on you to begin with? Why would you need to roll dice to evade a shot that can't hit you? I'm sure there is a simple answer to this question but based on my limited knowledge it doesn't make any sense.

Thanks for your help guys.

Turrets can shoot outside their firing arcs, no ship has a 360 arc.

Autothrusters are generally understood to be a counter to Turrets. Those are what can still shoot you "out of arc."

I can see that if the primary weapon wasn't the turret but fixed forward facing. However. what if the turret is the primary weapon? Wouldn't the ship THEN have a 360 degree firing arc noted on the ship token? If not it seems like a wacky kind of rule.

Nope. The firing arc is the firing arc as printed on the ship token. Several abilities depend on the distinction between the printed firing arc and the 360 of a turret. Kavil, named Scum Y-wing pilot, gets an extra attack die when shooting at targets outside his firing arc. So he needs a turret to be able to use that ability. Similarly, named TIE fighter pilot Backstabber gets an extra attack die when attacking from outside someone's arc. He gets against a turreted ship as long as he is outside the printed arc on the token. This is addressed in the FAQ.

OK, I gotcha. Makes sense now. It's a bit of a game design thing. Thanks for your help!

Do note that while turrets do not have a 360 degree firing arc some ships do have an Auxiliary Firing which does count as a "firing arc" for a good many things. If you try sneaking in behind a Firespray your Autothrusters will do nothing to protect you unless you also happen to beyond R2 as well.

Also keep in mind that for a Firespray, the rear auxillary arc is considered "in arc" - so Autothrusters would only be in play if you are at range 3 in either front or rear arc.

Attacks on the sides - where you are outside of those printed arc - would also bring it into play.