Video #6 in a series by The Aircraft Engine Historical Society channel (www.enginehistory.org). In 1989, the Pratt & Whitney-Allison 578-DX was the second American ultra-high bypass propfan demonstrator engine to fly on a MD-80 test aircraft. Unique to the 578-DX was the use of a reduction gearbox designed for 13,000 horsepower to drive the twelve, swept, dual-rotation carbon fiber fan blades.