An aircraft gas turbine engine comprising: a turbocompressor; a buffer air system; a main compressor section; and an environmental control system comprising: a higher pressure tap associated with a higher pressure location in the main compressor section, and a lower pressure tap associated with a lower pressure location in the main compressor section, said lower pressure location being at a lower pressure than said higher pressure location, the lower pressure tap communicating to a first passage leading to a downstream outlet to be delivered to the aircraft, and having a second passage leading into a compressor section of the turbocompressor, the higher pressure tap leading into a turbine section of the turbocompressor such that air in the higher pressure tap drives the turbine section of the turbocompressor to in turn drive the compressor section of the turbocompressor; a turbine outlet receiving airflow exhausted from the turbine section of the turbocompressor; a compressor outlet receiving airflow exhausted from the compressor section of the turbocompressor; a combined outlet receiving airflow from the turbine outlet and the compressor outlet intermixing airflow and passing the mixed airflow to the downstream outlet to be delivered to the aircraft; and a buffer air outlet (112, 114) communicating airflow to the engine buffer air system, the buffer air outlet (112, 114) receiving airflow supplied to the turbocompressor, wherein the turbocompressor includes a housing supporting the compressor section of the turbocompressor, and the buffer air outlet (112, 114) is within the housing, and wherein the buffer air system is configured to utilize the airflow communicated thereto in a low pressure turbine section or a high pressure turbine section of the aircraft gas turbine engine. a turbocompressor; a buffer air system; a main compressor section; and an environmental control system comprising: a higher pressure tap associated with a higher pressure location in the main compressor section, and a lower pressure tap associated with a lower pressure location in the main compressor section, said lower pressure location being at a lower pressure than said higher pressure location, the lower pressure tap communicating to a first passage leading to a downstream outlet to be delivered to the aircraft, and having a second passage leading into a compressor section of the turbocompressor, the higher pressure tap leading into a turbine section of the turbocompressor such that air in the higher pressure tap drives the turbine section of the turbocompressor to in turn drive the compressor section of the turbocompressor; a turbine outlet receiving airflow exhausted from the turbine section of the turbocompressor; a compressor outlet receiving airflow exhausted from the compressor section of the turbocompressor; a combined outlet receiving airflow from the turbine outlet and the compressor outlet intermixing airflow and passing the mixed airflow to the downstream outlet to be delivered to the aircraft; and a buffer air outlet (112, 114) communicating airflow to the engine buffer air system, the buffer air outlet (112, 114) receiving airflow supplied to the turbocompressor, wherein the turbocompressor includes a housing supporting the compressor section of the turbocompressor, and the buffer air outlet (112, 114) is within the housing, and wherein the buffer air system is configured to utilize the airflow communicated thereto in a low pressure turbine section or a high pressure turbine section of the aircraft gas turbine engine. a higher pressure tap associated with a higher pressure location in the main compressor section, and a lower pressure tap associated with a lower pressure location in the main compressor section, said lower pressure location being at a lower pressure than said higher pressure location, the lower pressure tap communicating to a first passage leading to a downstream outlet to be delivered to the aircraft, and having a second passage leading into a compressor section of the turbocompressor, the higher pressure tap leading into a turbine section of the turbocompressor such that air in the higher pressure tap drives the turbine section of the turbocompressor to in turn drive the compressor section of the turbocompressor; a turbine outlet receiving airflow exhausted from the turbine section of the turbocompressor; a compressor outlet receiving airflow exhausted from the compressor section of the turbocompressor; a combined outlet receiving airflow from the turbine outlet and the compressor outlet intermixing airflow and passing the mixed airflow to the downstream outlet to be delivered to the aircraft; and a buffer air outlet (112, 114) communicating airflow to the engine buffer air system, the buffer air outlet (112, 114) receiving airflow supplied to the turbocompressor, wherein the turbocompressor includes a housing supporting the compressor section of the turbocompressor, and the buffer air outlet (112, 114) is within the housing, and wherein the buffer air system is configured to utilize the airflow communicated thereto in a low pressure turbine section or a high pressure turbine section of the aircraft gas turbine engine.