| CPC F02C 9/28 (2013.01) [B64D 27/10 (2013.01); B64D 37/04 (2013.01); G08G 5/32 (2025.01)] | 14 Claims |

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1. A method of operating an aircraft comprising a gas turbine engine and a fuel tank arranged to provide fuel to the gas turbine engine, the method comprising:
determining at least one fuel characteristic of the fuel arranged to be provided to the gas turbine engine; and
proposing or initiating a change to a flight profile of the aircraft based on the at least one fuel characteristic,
wherein the at least one fuel characteristic of the fuel comprises at least one of:
i. percentage of sustainable aviation fuel in the fuel;
ii. percentage of nitrogen-containing species in the fuel;
iii. presence or percentage of a tracer species or trace element in the fuel;
iv. hydrogen to carbon ratio of the fuel;
v. percentage composition information for hydrocarbons present in the fuel;
vi. naphthalene content of the fuel;
vii. oxygen content of the fuel;
viii. thermal stability of the fuel; and
ix. level of coking of the fuel.
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