Environmental control system supply precooler bypass

A gas turbine engine compressor bleed air supply system comprising:

• a compressor air supply precooler for cooling compressor bleed air from a bleed air source and operably connected in supply flow communication with an environmental control system operable for conditioning cabin air and/or providing cooling for avionics and/or other equipment,
• a bleed air outlet line connecting the compressor air supply precooler to the environmental control system,
• the bleed air source being selectable between low and high pressure bleed air sources of a gas turbine engine high pressure compressor,
• the precooler including an air-to-air heat exchanger in fluid communication with a source of cooling air and operable for cooling the compressor bleed air,
• the source of cooling air being a fan of the gas turbine engine,
• a variable bypass valve disposed between the bleed air source and environmental control system, and
• the variable bypass valve operable for bypassing at least a portion of the compressor bleed air around the heat exchanger.

An aircraft comprising:

• two or more aircraft gas turbine engines and an environmental control system within the aircraft,
• each aircraft gas turbine engine including in serial flow communication a fan, a high pressure compressor, an annular combustor, a high pressure turbine for powering the high pressure compressor, and a low pressure turbine for powering the fan,
• an annular nacelle surrounding the fan,
• a core cowl surrounding the high pressure compressor, the combustor, and the high pressure turbine,
• an annular bypass duct located radially between the annular nacelle and the core cowl,
• a compressor air supply precooler for cooling compressor bleed air from a bleed air source in the high pressure compressor,
• the compressor air supply precooler operably connected in supply flow communication with the environmental control system operable for conditioning cabin air and/or providing cooling for avionics and/or other equipment,
• a bleed air outlet line connecting the compressor air supply precooler to the environmental control system,
• the precooler including an air-to-air heat exchanger in fluid communication with a source of cooling air from the bypass duct,
• the source of cooling air being a fan of the gas turbine engine,
• the precooler operable for cooling the compressor bleed air,
• a variable bypass valve disposed between the bleed air source and environmental control system, and
• the variable bypass valve operable for bypassing at least a portion of the compressor bleed air around the heat exchanger.

A method for supplying compressor bleed air to an environmental control system of an aircraft:

• flowing low pressure bleed air bled from a single low pressure source to a compressor air supply precooler for cooling the low pressure bleed air,
• flowing the low pressure bleed air to an environmental control system operable for conditioning cabin air and/or providing cooling for avionics and/or other equipment,
• flowing the low pressure bleed air through a bleed air outlet line connecting the compressor air supply precooler to the environmental control system,
• the precooler being an air-to-air heat exchanger in fluid communication with a source of cooling air and operable for cooling the compressor bleed air,
• the source of cooling air being a fan of the gas turbine engine,
• a variable bypass valve disposed between the bleed air source and environmental control system,
• the variable bypass valve operable for bypassing at least a portion of the compressor bleed air around the heat exchanger,
• the single low pressure source being an intermediate or lower pressure stage of a high pressure HP compressor wherein the intermediate or lower pressure stage is located between a first stage and a last stage of the of the high pressure HP compressor,
• detecting one engine out aircraft operating condition during approach or loitering of the aircraft, and
• increasing a thrust level of the engine sufficiently to meet a predetermined or calculated minimum level of pressure of the compressor bleed air from the single low pressure source.