A gas turbine engine (200, 200', 200") for mounting to an airframe of an aircraft, comprising: an engine core comprising a compressor, a combustor, a turbine, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; a bifurcation spanning a bypass duct defined between the engine core and a nacelle surrounding the gas turbine engine, the bifurcation comprising aerodynamically shaped fairings defining an interior space therebetween; a mechanical power offtake; and a cabin blower system configured to be driven by the mechanical power offtake (118, 118', 118") and comprising: a cabin blower compressor configured to receive air from the engine through an air inlet, compress the air and output the compressed air through an air outlet; an electric variator comprising a first electrical machine, a second electrical machine, and a power management system electrically interconnecting the first and second electrical machines and controlling whether each of the first and second electrical machines operates as a motor or a generator; and a differential gearbox having a first input mechanically connected to the mechanical power offtake and to a shaft of the first electrical machine, a second input mechanically connected to a shaft of the second electrical machine, and an output to drive the cabin blower compressor; wherein the cabin blower system is arranged in the interior space of the bifurcation, and the gas turbine engine further comprises a heat exchanger arranged in the interior space of the bifurcation to cool the electric variator. an engine core comprising a compressor, a combustor, a turbine, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; a bifurcation spanning a bypass duct defined between the engine core and a nacelle surrounding the gas turbine engine, the bifurcation comprising aerodynamically shaped fairings defining an interior space therebetween; a mechanical power offtake; and a cabin blower system configured to be driven by the mechanical power offtake (118, 118', 118") and comprising: a cabin blower compressor configured to receive air from the engine through an air inlet, compress the air and output the compressed air through an air outlet; an electric variator comprising a first electrical machine, a second electrical machine, and a power management system electrically interconnecting the first and second electrical machines and controlling whether each of the first and second electrical machines operates as a motor or a generator; and a differential gearbox having a first input mechanically connected to the mechanical power offtake and to a shaft of the first electrical machine, a second input mechanically connected to a shaft of the second electrical machine, and an output to drive the cabin blower compressor; a cabin blower compressor configured to receive air from the engine through an air inlet, compress the air and output the compressed air through an air outlet; an electric variator comprising a first electrical machine, a second electrical machine, and a power management system electrically interconnecting the first and second electrical machines and controlling whether each of the first and second electrical machines operates as a motor or a generator; and a differential gearbox having a first input mechanically connected to the mechanical power offtake and to a shaft of the first electrical machine, a second input mechanically connected to a shaft of the second electrical machine, and an output to drive the cabin blower compressor; wherein the cabin blower system is arranged in the interior space of the bifurcation, and the gas turbine engine further comprises a heat exchanger arranged in the interior space of the bifurcation to cool the electric variator.