Developed by United Technologies Research Center, a distortion-tolerant fan was scale tested at NASA and coped with flow distortion from ingesting the boundary layer close to the upper fuselage surface. As a compact core limits blade tip clearances issues due to bending but cannot house the fan to low-pressure turbine driveshaft, Pratt & Whitney turned the core backwards, similar to PT6 arrangement, with hot gas discharged forward through a low-pressure power turbine connected to the fan via a short shaft and a gearbox. To avoid the risk of an uncontained engine failure causing the second engine to fail, the cores are angled by 50° since they are no longer mechanically linked to the fan, with low pressure losses since only the core flow is turned.