Upvote:3
The arrival flight is the flight number of the flight which first lands in the US having departed from another country. So this will be the flight which lands in Charlotte. (Example: AA1706)
The departure flight is the flight number of the flight which takes off from the US and lands in another country. (Example: AA1707)
Don't worry if you have to change your itinerary later. These are used in part to verify that your proposed itinerary makes sense with the rest of your application.