United Airlines Chairman Stephen Wolf says he wants to increase his airline's fleet by about 100 planes to 500 over the next five years. United now has 129 planes on order from Boeing Co., but Wolf said "we'll need more" for expansion and to replace older aircraft. Wolf said rapid growth in travel, especially across the Pacific, could push the number of planes needed even higher. The Chicago-based carrier is taking delivery of four new planes a month and will have 403 aircraft at the end of the year. Many of those on order will replace older planes in the early 1990s.