A gas turbine engine is provided, including an air inlet in fluid communication with a compressor, a combustor, a compressor turbine, and a power turbine. The compressor and compressor turbine may be mounted on a first drive shaft, and the power turbine may be mounted on a second shaft. The engine further includes an engagement mechanism adapted to selectively engage the first drive shaft to the second drive shaft, wherein the first drive shaft and second drive shaft rotate at substantially the same speed when the engagement mechanism is engaged. The disclosed multi-spool gas turbine engine provides improved part power fuel consumption at reduced output shaft speeds. The proposed invention can relate to turbines with two or more gas generator spools.