December 1990. Component improvements enabled it to achieve YF120 thrust levels at lower temperatures. The USAF ultimately chose the Pratt & Whitney's F119 proposal for full-scale development and production. The more ambitious F120 design was judged to be riskier, and General Electric also accrued fewer testing hours than Pratt & Whitney. Further developments The YF120 was also proposed as the basis for a more exotic engine, the Turbine-Based Combined Cycle (TBCC) engine that was to be used in demonstrator aircraft like the X-43B and future hypersonic aircraft. Specifically, the YF120 was to be the basis for the Revolutionary Turbine Accelerator (RTA-1). The variable cycle technology used in the YF120 would be extended to not only turn the engine into a turbojet but also into a ramjet. In that mode all airflow would bypass the core and be diverted into the afterburner-like "hyperburner" where it would be combusted like a ramjet. This proposed engine was to accelerate from 0 to Mach 4.1 (at 56,000 ft) in eight minutes. Technology from the YF120 has been applied to subsequent GE designs; in the 1990s, GE and Rolls-Royce began jointly developing the F136 engine for the Joint Strike Fighter program. While drawing from lessons learned from the YF120, the F136 is a conventional fixed-bypass design; it also leveraged advances in turbine engine technology from the Integrated High Performance Turbine Engine Technology (IHPTET) program, which continued developments from ATEGG and JTDE. Despite better performance potential than the incumbent Pratt & Whitney F135, The F136 was eventually cancelled due to a lack of funding. Despite not selecting the YF120 for the ATF, the USAF would further the development of variable cycle engine technology through the Versatile Affordable Advanced Turbine Engines (VAATE), a joint government and industry effort that aims to address future turbine engine needs. Under the VAATE, the Adaptive Versatile Engine Technology (ADVENT) program would continue the development of variable cycle turbine engine technology into an adaptive three-stream architecture. The follow-on Adaptive Engine Technology Demonstrator (AETD), Adaptive Engine Transition Program (AETP) and the Next Generational Adaptive Propulsion (NGAP) resulted in the development of the GE XA100 and the P&W XA101 for potential reengining of the Lockheed Martin F-35 and adaptive engines for the Next Generation Air Dominance and F/A-XX programs, successors to the ATF. Design The YF120 is a twin-spool axial-flow afterburning turbofan. The design consists of a two-stage fan driven by the single-stage low-pressure