The term EXTRA COST FOR AN AIRLINE PASSENGER can be summarized as the additional fees that a passenger may have to pay when flying with an airline. This could include things such as baggage fees, seat selection fees, or other services that are not included in the base ticket price. The crossword solution for this term is PET, which stands for Passenger Extra Tax. This is a fee that airlines charge passengers for certain services, such as priority boarding or extra legroom.