As you enter the Passenger Car all you see is empty seats, at the end you see another locked door. This time the lock requires three letters to be entered. Allowing you access the next car.
Confused, you look around and on some of the seats, you find some boarding passes left behind. Maybe they could be helpful for you to get to the next car. Still confused you find a cell phone left behind that has a message on it.
Enter the letters into the lock (needs 3 letters)