Another airline joins the growing list of companies charging flyers for checking extra luggage.Northwest Airlines said Friday it will begin charging $25 to check a passenger's second bag. Coach class customers will not be charged to check one piece of luggage. Members of northwest's higher frequent flyer programs may still check two bags at no additional charge. American Airlines is also said to be contemplating an extra baggage fee. United, Delta and U.S. Airways have already instituted the fee for their customers. The airlines say the fee helps offset high fuel prices.