AC = 10 + the pilot’s ranks in the Piloting skill + the ship’s armor bonus + modifier based on the ship’s size + bonuses and penalties from successful or failed stunts and actions
Determining The Outcome
Compare the result of the gunnery check to the target’s Armor Class (AC) or Target Lock (TL), depending on the weapon used. If you attack with a direct-fire weapon (see page 303) and the result of the gunnery check equals or exceeds the target’s AC, you hit the target and damage is determined as normal (see Damage below). A target’s AC is determined using the following formula.
If the attack is made with a tracking weapon such as a missile launcher (see page 303) and the result of the gunnery check equals or exceeds the target’s TL, the tracking weapon’s projectile moves its speed toward the target, making turns during this movement as needed (a projectile from a tracking weapon has perfect maneuverability). If it intercepts the target before it reaches the end of its movement, it explodes and deals damage as normal (see Damage below). If not, attempt a new gunnery check at the start of the next gunnery phase to determine whether the projectile continues to move toward the target; you don’t receive any bonuses from computer systems or actions by your fellow crew members from previous rounds or the current round, but you can take penalties, such as from an enemy science officer’s improve countermeasures action (see page 325). If the result of a gunnery check for a tracking weapon is ever less than the target’s TL, the weapon’s projectile is destroyed and removed from play. A target’s TL is determined using the following formula.
Source
Core Rulebook pg. 320