Gas turbine engine with an improved thermal management system

A method of operating a gas turbine engine for an aircraft, the method comprising providing a gas turbine engine comprising:

• an engine core comprising a compressor, a combustor, a turbine, and a core shaft connecting the turbine to the compressor;
• a fan comprising a plurality of fan blades and arranged upstream of the engine core;
• turbomachinery bearings;
• a power gearbox adapted to drive the fan at a lower rotation speed than the turbine;
• and
• a heat management system configured to provide lubrication and cooling to the power gearbox and turbomachinery bearings, and comprising a pipe assembly adapted to provide a lubricant flow to the power gearbox and turbomachinery bearings, wherein the pipe assembly comprises a first lubricant circuit adapted to provide a first lubricant flow and a second lubricant circuit adapted to provide a second lubricant flow, at least one air-lubricant heat exchanger configured to dissipate a first amount of heat to a first heat sink, and at least one fuel-lubricant heat exchanger configured to dissipate a second amount of heat to a second heat sink, and a lubricant tank in fluid communication with, and feeding lubricant to, the first and second lubricant circuits, wherein the tank has a first outlet feeding lubricant to the first lubricant circuit, and a second outlet, separate from the first outlet, feeding lubricant to the second lubricant circuit, wherein the sum of the first amount of heat and the second amount of heat is the heat generated by the power gearbox and turbomachinery bearings and removed by the lubricant flow;
• wherein the first heat sink is air and the second heat sink is fuel,
• wherein a first proportion of heat generated by the power gearbox and the turbomachinery and dissipated to air is defined as
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• first
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• 111
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• 85
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• MTO
• at 85% of a core shaft maximum take-off speed, and
• the method comprises the step of operating the at least one air-lubricant heat exchanger and the at least one fuel-lubricant heat exchanger to provide the first proportion in the range of from 0.30 to 0.70.