A gas turbine engine assembly comprising: at least one propelling gas turbine engine comprising a fan, a core engine downstream from the fan, and a plurality of extraction points (124, 122, 120) via which air is extractable from the propelling gas turbine engine to an auxiliary engine for generating power; a control valve assembly coupled in flow communication to said at least one propelling gas turbine engine, said control valve assembly comprising a low pressure source control valve and a high pressure source control valve; and said auxiliary engine comprising a compressor, at least one turbine downstream of said compressor, and an inlet to said compressor, said inlet coupled in flow communication with said control valve assembly, wherein a portion of airflow entering said at least one propelling engine is extractable via the extraction points for use by said auxiliary engine and said control valve assembly is operable to control the flow of extracted airflow from said at least one propelling engine to said inlet of said compressor of said auxiliary engine, wherein said high pressure source control valve of said control valve assembly is coupled to a first of said plurality of extraction points (120, 122, 124) for selectively controlling a flow of high-pressure airflow to said auxiliary engine and wherein said low pressure source control valve of said control valve assembly is coupled to a second (122, 124) of said plurality of extraction points for selectively controlling a flow of low-pressure airflow to said auxiliary engine such that during operations at high altitudes said auxiliary engine receives airflow at a high pressure from said high pressure source control valve, during operations at low altitudes said auxiliary engine receives airflow at a low pressure from said low pressure source control valve, and during operations at intermediate altitudes said auxiliary engine receives a blended airflow at an intermediate pressure from both said low pressure source control valve and said high pressure source control valve. at least one propelling gas turbine engine comprising a fan, a core engine downstream from the fan, and a plurality of extraction points (124, 122, 120) via which air is extractable from the propelling gas turbine engine to an auxiliary engine for generating power; a control valve assembly coupled in flow communication to said at least one propelling gas turbine engine, said control valve assembly comprising a low pressure source control valve and a high pressure source control valve; and said auxiliary engine comprising a compressor, at least one turbine downstream of said compressor, and an inlet to said compressor, said inlet coupled in flow communication with said control valve assembly, wherein a portion of airflow entering said at least one propelling engine is extractable via the extraction points for use by said auxiliary engine and said control valve assembly is operable to control the flow of extracted airflow from said at least one propelling engine to said inlet of said compressor of said auxiliary engine, wherein said high pressure source control valve of said control valve assembly is coupled to a first of said plurality of extraction points (120, 122, 124) for selectively controlling a flow of high-pressure airflow to said auxiliary engine and wherein said low pressure source control valve of said control valve assembly is coupled to a second (122, 124) of said plurality of extraction points for selectively controlling a flow of low-pressure airflow to said auxiliary engine such that during operations at high altitudes said auxiliary engine receives airflow at a high pressure from said high pressure source control valve, during operations at low altitudes said auxiliary engine receives airflow at a low pressure from said low pressure source control valve, and during operations at intermediate altitudes said auxiliary engine receives a blended airflow at an intermediate pressure from both said low pressure source control valve and said high pressure source control valve.