Multiple core variable cycle gas turbine engine and method of operation

A gas turbine engine system (10) includes a fan assembly (12), a low pressure compressor (14), a low pressure turbine (16), a plurality of engine cores (30-1 to 30-n) including a first engine core and a second engine core, and a control assembly (36). A primary flowpath (F P ) is defined through the fan assembly (12), the low pressure compressor (14), the low pressure turbine (16), and the active engine cores. Each engine core includes a high pressure compressor (40), a combustor (38) downstream from the high pressure compressor (40), and a high pressure turbine (42) downstream from the combustor (38). The control assembly (36) is configured to control operation of the plurality of engine cores (30-1 to 30-n) such that in a first operational mode the first and the second engine cores are active to generate combustion products and in a second operational mode the first engine core is active to generate combustion products while the second engine core is idle.