A gas turbine engine, comprising; a compressor structured to compress an airflow received at the compressor and to output the compressed airflow as a compressor discharge airflow; a combustor in fluid communication with said compressor, said combustor being structured to combust a mixture of a fuel and at least some of said compressor discharge airflow to generate a hot working airflow; a turbine in fluid communication with said combustor, said turbine being configured to extract a mechanical power from said hot working airflow; a shaft coupled to said turbine, said shaft being configured to receive and transmit said mechanical power from said turbine; a first rotating load powered by said shaft; a second rotating load powered by said shaft; and a transmission system including: a geartrain coupled to said shaft; a clutching mechanism coupled to said shaft in parallel to said geartrain, wherein said clutching mechanism includes a clutch and a positive locking mechanism arranged in parallel relationship to the clutch, wherein the clutch couples the shaft to the second rotating load through alternating engagement of one of the positive locking mechanism and the geartrain such that when the positive locking mechanism is engaged the second rotating load is driven by the shaft at a same speed as the first rotating load and when the geartrain is engaged the second rotating load is driven at a speed less than the speed of the first rotating load, said transmission system being structured to selectively vary a speed at which power is supplied from said shaft to said second rotating load relative to a speed of at least one of said shaft and said first rotating load, wherein to increase extraction of mechanical power the second rotating load rotates at a same speed as the first rotating load. a compressor structured to compress an airflow received at the compressor and to output the compressed airflow as a compressor discharge airflow; a combustor in fluid communication with said compressor, said combustor being structured to combust a mixture of a fuel and at least some of said compressor discharge airflow to generate a hot working airflow; a turbine in fluid communication with said combustor, said turbine being configured to extract a mechanical power from said hot working airflow; a shaft coupled to said turbine, said shaft being configured to receive and transmit said mechanical power from said turbine; a first rotating load powered by said shaft; a second rotating load powered by said shaft; and a transmission system including: a geartrain coupled to said shaft; a clutching mechanism coupled to said shaft in parallel to said geartrain, a geartrain coupled to said shaft; a clutching mechanism coupled to said shaft in parallel to said geartrain, wherein said clutching mechanism includes a clutch and a positive locking mechanism arranged in parallel relationship to the clutch, wherein the clutch couples the shaft to the second rotating load through alternating engagement of one of the positive locking mechanism and the geartrain such that when the positive locking mechanism is engaged the second rotating load is driven by the shaft at a same speed as the first rotating load and when the geartrain is engaged the second rotating load is driven at a speed less than the speed of the first rotating load, said transmission system being structured to selectively vary a speed at which power is supplied from said shaft to said second rotating load relative to a speed of at least one of said shaft and said first rotating load, wherein to increase extraction of mechanical power the second rotating load rotates at a same speed as the first rotating load.