In the 1980s, Douglas modified the MD-80 prototype, turning it into a testbed for ultra-high-bypass (UHB) engines made by both General Electric and Allison. Propfan engines were substituted for rear-mounted turbofan engines. The technology had great potential for fuel economy, but steady fuel prices of the 1980s, and concerns about the potential for difficult engine maintenance and a lack of public acceptance for turbo-fan powered jetliners ended development of the MD-80 turbofan.