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 , each of the plurality of ports being configured to provide bleed air from an engine (405;805) of the airplane to the environmental control system , wherein the plurality of ports 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 , each of the plurality of ports being configured to provide bleed air from an engine (405;805) of the airplane to the environmental control system , wherein the plurality of ports 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 . <EOS>