The Pratt & Whitney/Allison 578-DX was an experimental aircraft engine, a hybrid between a turbofan and a turboprop known as a propfan. The 578-DX was developed as a joint venture between Pratt & Whitney and Allison. Unlike the competing General Electric GE-36 UDF, the 578-DX was fairly conventional, having a reduction gearbox between the LP turbine and the propfan blades. Noise considerations, plus a significant reduction in the real cost of aviation fuel, brought the NASA funded program to a halt.
The engine was tested with 11.6 ft propfans in 1989 on a modified MD-80.