An airplane comprising: an environmental control system configured to provide pressurized air to a chamber of the airplane, the environmental control system including a compressing device, an outlet and a condenser, the compressing device comprising a compressor, a first turbine, a second turbine, a fan, and a shaft, the compressor, the first turbine and the second turbine mounted on the shaft; and a bleed system (400;800) comprising a plurality of ports (415,420,425), each of the plurality of ports (415,420,425) being configured to provide bleed air from an engine (405;805) of the airplane to the environmental control system, wherein the plurality of ports (415,420,425) includes at least a first port selected for an idle condition, a second port selected for a hot day cruise condition, and a third port selected for a standard operating condition, wherein the bleed system (400;800) operates in a first mode, a second mode, or a third mode to provide the bleed air to the environmental control system from the first port, the second port, or the third port respectively, wherein the second port comprises an intermediate pressure port and the second mode is used for the hot day cruise condition, wherein the third port comprises a low pressure port and the third mode is used for the standard operating condition, wherein the bleed system (400;800) includes a precooler (410;704), and wherein the precooler (410;704) is bypassed by the bleed air during the third mode; characterised in that, during the hot day cruise condition: a first portion of the bleed air is extracted from the engine (405; 805), expanded across the second turbine, and exhausted to ambient air; and the compressor is used to boost a pressure of a second portion of the bleed air received by the compressor based on power from both the first turbine and the second turbine. an environmental control system configured to provide pressurized air to a chamber of the airplane, the environmental control system including a compressing device, an outlet and a condenser, the compressing device comprising a compressor, a first turbine, a second turbine, a fan, and a shaft, the compressor, the first turbine and the second turbine mounted on the shaft; and a bleed system (400;800) comprising a plurality of ports (415,420,425), each of the plurality of ports (415,420,425) being configured to provide bleed air from an engine (405;805) of the airplane to the environmental control system, wherein the plurality of ports (415,420,425) includes at least a first port selected for an idle condition, a second port selected for a hot day cruise condition, and a third port selected for a standard operating condition, wherein the bleed system (400;800) operates in a first mode, a second mode, or a third mode to provide the bleed air to the environmental control system from the first port, the second port, or the third port respectively, wherein the second port comprises an intermediate pressure port and the second mode is used for the hot day cruise condition, wherein the third port comprises a low pressure port and the third mode is used for the standard operating condition, wherein the bleed system (400;800) includes a precooler (410;704), and wherein the precooler (410;704) is bypassed by the bleed air during the third mode; characterised in that, during the hot day cruise condition: a first portion of the bleed air is extracted from the engine (405; 805), expanded across the second turbine, and exhausted to ambient air; and the compressor is used to boost a pressure of a second portion of the bleed air received by the compressor based on power from both the first turbine and the second turbine. a first portion of the bleed air is extracted from the engine (405; 805), expanded across the second turbine, and exhausted to ambient air; and the compressor is used to boost a pressure of a second portion of the bleed air received by the compressor based on power from both the first turbine and the second turbine.