My question is how can a jet engine be both a turbo-prop and a pure jet engine? Sure, a turbo-prop develops a bit of thrust, but most of the combustion energy is converted to torque by the last stage turbine blades, which are certainly a non-removable part of the engine. This idea seems to have much built in inefficiency and/or extra weight. Am I missing something? Do they intend to fly extra engines just for landing?