I don't know if it's the longest but it's long enough that you get a chance to take in the scenery. Pretty amazing ride! And you have to brake yourself. 😬 You start to brake when you see the guides frantically waving their arms.

Update: So, I just found out that the longest zipline in the world is the Parque de Aventura Barrancas del Cobre in Copper Canyon, Mexico. Over 8,350 feet long (more than a mile and a half!), and with a 17% grade that drops you almost 1,500 feet... 84 mph. Yikes!