Method of operating a gas turbine engine

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

• an engine core comprising a turbine, a compressor, a combustor arranged to combust a fuel, and a core shaft connecting the turbine to the compressor;
• a fan located upstream of the engine core;
• a gearbox that receives an input from the core shaft and outputs drive to the fan so as to drive the fan at a lower rotational speed than the core shaft;
• an oil loop system arranged to supply oil to the gearbox;
• and
• a heat exchange system comprising:
• an air-oil heat exchanger through which the oil in the oil loop system flows;
• a fuel-oil heat exchanger through which the oil in the oil loop system and the fuel flow such that heat is transferred between the oil and the fuel;
• and
• at least one valve arranged to allow a proportion of the oil sent via at least one of the heat exchangers to be varied,
• the method comprising controlling the at least one valve such that, under idle conditions, an oil flow ratio of:
• rate
• ⁢
• of
• ⁢
• oil
• ⁢
• flow
• ⁢
• into
• ⁢
• air
• -
• oil
• ⁢
• heat
• ⁢
• exchanger
• ⁢
• (
• m
• 3
• ⁢
• s
• -
• 1
• )
• rate
• ⁢
• of
• ⁢
• oil
• ⁢
• flow
• ⁢
• into
• ⁢
• fuel
• -
• oil
• ⁢
• heat
• ⁢
• exchanger
• ⁢
• (
• m
• 3
• ⁢
• s
• -
• 1
• )
• is in the range from 0.62 to 5.29.