Complex sentence: Since Guam is outside the United States customs jurisdiction, passengers from all arrival flights go through GCQA inspection, and departing passengers on the Honolulu-bound flight (currently the only Stateside departure) go through a normal USCBP customs inspection upon arrival.
Split into simpler sentences: Since Guam is outside the United States customs jurisdiction, passengers from all arrival flights go through GCQA inspection. Passengers bound for Honolulu (currently the only Stateside flight) go through a normal USCBP customs inspection upon arrival.