A system for supplying conditioned air to an inerting apparatus of an aircraft, the system comprising: an inerting apparatus; and an air supply system arranged to supply air to the inerting apparatus, the air supply system comprising: a first air supply source; a first flow path fluidly connecting the first air supply source to an inerting apparatus; a compressor device driven by a turbine; a second air supply source; a second flow path fluidly connecting the second air supply source to the turbine of the compressor device; a first valve located within the first flow path and configured to be open in a first state and closed in a second state, the first valve configured to allow a supply of air to flow from the first air supply source to the inerting apparatus directly; a second valve located within the second flow path and configured to be closed in the first state and open in the second state, the second valve configured to allow a supply of air to flow from the second air supply source to drive the turbine of the compressor device; and a heat exchanger configured to condition the compressed air prior to being supplied to the inerting apparatus; wherein, when in the second state, the compressor device is operated to compress air from the first air supply source prior to the air being supplied to the inerting apparatus; characterised in that: the heat exchanger is upstream of the turbine within the second flow path. an inerting apparatus; and an air supply system arranged to supply air to the inerting apparatus, the air supply system comprising: a first air supply source; a first flow path fluidly connecting the first air supply source to an inerting apparatus; a compressor device driven by a turbine; a second air supply source; a second flow path fluidly connecting the second air supply source to the turbine of the compressor device; a first valve located within the first flow path and configured to be open in a first state and closed in a second state, the first valve configured to allow a supply of air to flow from the first air supply source to the inerting apparatus directly; a second valve located within the second flow path and configured to be closed in the first state and open in the second state, the second valve configured to allow a supply of air to flow from the second air supply source to drive the turbine of the compressor device; and a heat exchanger configured to condition the compressed air prior to being supplied to the inerting apparatus; wherein, when in the second state, the compressor device is operated to compress air from the first air supply source prior to the air being supplied to the inerting apparatus; characterised in that: the heat exchanger is upstream of the turbine within the second flow path. a first air supply source; a first flow path fluidly connecting the first air supply source to an inerting apparatus; a compressor device driven by a turbine; a second air supply source; a second flow path fluidly connecting the second air supply source to the turbine of the compressor device; a first valve located within the first flow path and configured to be open in a first state and closed in a second state, the first valve configured to allow a supply of air to flow from the first air supply source to the inerting apparatus directly; a second valve located within the second flow path and configured to be closed in the first state and open in the second state, the second valve configured to allow a supply of air to flow from the second air supply source to drive the turbine of the compressor device; and a heat exchanger configured to condition the compressed air prior to being supplied to the inerting apparatus; wherein, when in the second state, the compressor device is operated to compress air from the first air supply source prior to the air being supplied to the inerting apparatus; characterised in that: the heat exchanger is upstream of the turbine within the second flow path.