Determination of fuel characteristics

1. A method of generating a maintenance schedule for an aircraft including one or more gas turbine engines powered by an aviation fuel, the method comprising:

determining one or more fuel characteristics of the fuel; and

generating a maintenance schedule according to the one or more fuel characteristics.

2. The method of claim 1 , wherein generating the maintenance schedule comprises modifying an existing maintenance schedule for the aircraft according to the determined one or more fuel characteristics.

3. The method of claim 2 , wherein generating the maintenance schedule comprises comparing the one or more determined fuel characteristics to an expected fuel characteristic and the existing maintenance schedule is associated with the expected fuel characteristic and modifying the existing maintenance schedule is done in response to determining a deviation from the expected fuel characteristic.

4. The method of claim 1 , wherein generating the maintenance schedule comprises comparing the one or more determined fuel characteristics to an expected fuel characteristic.

5. The method of claim 1 , wherein determining the one or more fuel characteristics comprises making periodic determinations of a fuel characteristic or characteristics.

6. The method of claim 1 , wherein the one or more fuel characteristics include any one or more of:

(i) a hydrocarbon distribution of the fuel;

(ii) a percentage of sustainable aviation fuel in the fuel;

(iii) an aromatic hydrocarbon content of the fuel; and/or

(iv) an indication that the fuel is a fossil fuel e.g. kerosene.

7. The method of claim 1 , wherein determining the one or more fuel characteristics comprises measuring a change in the properties of a sensor component exposed to the fuel used to power the one or more gas turbine engines.

8. The method of claim 7 , wherein the one or more fuel characteristics indicate a threshold level of fuel coking or surface deposit formation has occurred, and optionally:

wherein the sensor component comprises a piezoelectric crystal and determining the one or more fuel characteristics comprises measuring a vibration parameter of the piezoelectric crystal.

9. The method of claim 7 , wherein the sensor component comprises a seal material, and the one or more fuel characteristics indicate whether a threshold level of swell of the seal material exposed to the fuel has occurred, and preferably: the seal material is the same as at least one seal provided in a fuel system of the one or more gas turbine engines; and/or is a nitrile seal material.

10. A method of maintaining an aircraft, the method comprising:

generating a maintenance schedule according to the method of claim 1 ; and

performing maintenance on the aircraft according to the generated maintenance schedule.

11. A maintenance schedule generation system for generating a maintenance schedule for an aircraft including one or more gas turbine engines, the maintenance schedule generation system comprising:

a fuel characteristic determination module configured to determine one or more fuel characteristics of a fuel provided to the one or more gas turbine engines of the aircraft; and

a maintenance schedule generation module configured to generate a maintenance schedule according to the one or more fuel characteristics.

12. The maintenance schedule generation system of claim 11 , wherein the maintenance schedule generation module is configured to modify an existing maintenance schedule for the aircraft according to the determined one or more fuel characteristics.

13. The maintenance schedule generation system of claim 11 , wherein the maintenance schedule generation module is configured to compare the one or more determined fuel characteristics to an expected fuel characteristic.

14. The maintenance schedule generation system of claim 13 , wherein the maintenance schedule generation module is configured to modify an existing maintenance schedule for the aircraft according to the determined one or more fuel characteristics and the existing maintenance schedule is associated with the expected fuel characteristic, and the maintenance schedule generation module is configured to modify the existing maintenance schedule in response to determining a deviation from the expected fuel characteristic.

15. The maintenance schedule generation system of claim 11 , wherein the fuel characteristic determination module is configured to perform periodic determinations of the one or more fuel characteristics.

16. The maintenance schedule generation system of claim 11 , wherein the one or more fuel characteristics include any one or more of:

(i) a hydrocarbon distribution of the fuel;

(ii) a percentage of sustainable aviation fuel in the fuel;

(iii) an aromatic hydrocarbon content of the fuel; and/or

(iv) an indication that the fuel is a fossil fuel e.g. kerosene.

17. The maintenance schedule generation system of claim 11 , wherein the fuel characteristic determination module is arranged to receive a sensor parameter indicative of a measured change in the properties of a sensor component exposed to the fuel used to power the one or more gas turbine engines and base the determination of the one or more fuel characteristics on the received sensor parameter.

18. The maintenance schedule generation system of claim 17 , wherein the one or more fuel characteristics indicate a threshold level of fuel coking or surface deposit formation has occurred, and optionally:

wherein the sensor component is a piezoelectric crystal and determining the one or more fuel characteristics comprises measuring a vibration parameter of the piezoelectric crystal.

19. The maintenance schedule generation system of claim 17 , wherein the sensor component comprises a seal material and the one or more fuel characteristics indicate whether a threshold level of swell of the seal material exposed to the fuel has occurred, and preferably: the seal material is the same as at least one seal provided in a fuel system of the one or more gas turbine engines; and/or is a nitrile seal material.

20. An aircraft comprising:

one or more gas turbine engines, and

the maintenance schedule generation system of claim 11 .