Characters in Vehicles
A character in a vehicle fills one of several possible roles, which determines what the character can do. A character can fill several roles at once, but most roles may only be filled by one character at a time. For example, an X-wing pilot also acts as the vehicle's commander and gunner, while her astromech droid usually acts as a copilot, shield operator, and engineer. On the other hand, an Imperial-class Star Destroyer with thousands of crewmembers still has only one pilot, one commander, and so forth. You can change roles from round to round, but you can only start filling a particular role if no other crew member has filled that role since your last turn.
Pilot (Position)
The pilot of the vehicle controls its movement. Most vehicles have only one position from where the vehicle can be piloted. Piloting a vehicle is, at a minimum, a move action, which means that the pilot can do something else with his standard action and swift action. A vehicle can have only one pilot at one time. The pilot adds the vehicle's size modifier and Dexterity modifier on all Initiative and Pilot checks.
Copilot
A copilot can help the pilot by using the aid another action (see Aid Another). The copilot must be seated in a location where he can see in front of the vehicle and advise the pilot (in most cases, this location is the cockpit). Aiding the pilot is a standard action, leaving the copilot with a move action and swift action each round to do something else. A vehicle can have only one copilot at a time.
Gunner
Most military vehicles and some civilian vehicles have built-in weapons. Any weapon not controlled by the pilot or co-pilot requires a gunner to operate. A vehicle can have as many gunners as it has gunner positions.
Commander
The commander coordinates the various crewmembers and stations aboard the vehicle, analyzes the battle as it unfolds, and looks for weaknesses in the enemy's vehicles and tactics. A vehicle can only have one commander at a time.
System Operator
The system operator manages the vehicle's shields, sensors, and communications. A vehicle can only have one system operator at a time.
Engineer
The chief engineer keeps the ship running even as it takes debilitating damage to its systems, diverting power from overloaded circuits to keep the ship functional. The engineer also leads efforts to repair damage to the hull between battles. A vehicle can only have one chief engineer at a time.
Other Crew
Other crewmembers can fill many supporting roles, coordinating troops or starfighters, administering medical care, guarding sensitive areas, and providing general maintenance. These crewmembers can assist others on some skill l checks; for example, the members of a repair team may assist the chief engineer in his duties on capital ships.
Passenger
All other personnel aboard the vehicle are considered passengers. Passengers have no specific role in the vehicle's operation but may take actions aboard the vehicle or replace crewmembers as needed.