There is provided a blower assembly 400 for providing air to an airframe system, comprising a rotor 410 configured to be mechanically coupled to a spool 440 of a gas turbine engine 10 and a flow modifier 510, 520 configured to receive and/or direct flow to the rotor 410; wherein the blower assembly 400 is configured to permit relative movement between the rotor 410 and the flow modifier 510, 520 to move between: a compressor configuration in which the rotor 410 is configured to be driven to rotate by the spool 440 and to receive and compress air from the gas turbine engine 10, and discharge the compressed air for supply to the airframe system; and a turbine configuration in which the rotor 410 is configured to receive air from an external air source 470 to drive the spool 440 to rotate.