S gauge 4-6-6-4 by American Flyer by Lionel By Bob Keller | March 19, 2012 | Last updated on November 7, 2022 Email Newsletter Get the newest photos, videos, stories, and more from Trains.com brands. Sign-up for email today! Get Updates This Union Pacific Challenger from Lionel offers S gaugers a highly detailed, articulated loco that possesses the most advanced electronics in the S gauge world.