Gas turbine engine and oil system thereof

1. A gas turbine engine for an aircraft comprising:

an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor;

a core casing surrounding the engine core;

a core cowl providing an aerodynamic fairing which surrounds the engine core and the core casing;

an engine accessory gearbox driven by a take-off from the core shaft, and mounted between the core casing and the core cowl; and

an oil system having one or more oil pumps powered by the engine accessory gearbox for circulating lubricating oil around components of the engine including the engine accessory gearbox, and having an oil tank for receiving and storing oil scavenged from the engine components before recirculation thereto;

wherein the engine accessory gearbox and the oil tank are mounted between the core casing and the core cowl, with the oil tank being located forward of the engine accessory gearbox; and

wherein the gas turbine engine further comprises an oil fill line which extends from the engine accessory gearbox to an inlet port accessible from the core cowl, the oil tank being fillable from the inlet port via the fill line and the engine accessory gearbox.

2. The gas turbine engine according to claim 1 , wherein the engine accessory gearbox is mounted vertically beneath the core casing.

3. The gas turbine engine according to claim 1 , wherein the oil tank extends circumferentially around the core casing from bottom dead centre to top dead centre.

4. The gas turbine engine according to claim 1 , wherein the inlet port is accessible from the core cowl at a location rearward of the engine accessory gearbox.

5. The gas turbine engine according to claim 1 comprising:

a fan located upstream of the engine core, the fan comprising a plurality of fan blades;

an annular fan duct extending rearwardly from the fan for a flow of air bypassing the engine core; and

a fan cowl surrounding the annular fan duct and defining an exit for the bypass air flow form the fan duct;

wherein the inlet port is rearward of the bypass air exit from the fan cowl.

6. The gas turbine engine according to claim 1 further comprising:

a power 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.

7. The gas turbine engine according to claim 1 further comprising respective oil level sensors in the engine accessory gearbox and the oil tank for determining the amount of oil in the oil system.

8. The gas turbine engine according to claim 1 which is configured such that oil from the fill line collects in the engine accessory gearbox and is pumped to the oil tank from the engine accessory gearbox on engine startup.

9. The gas turbine engine according to claim 8 , wherein the oil collected in the engine accessory gearbox is pumped to the oil tank via a scavenge line connecting the engine accessory gearbox and the oil tank on engine startup.

10. The gas turbine engine according to claim 1 which is configured such that the oil tank is fillable by injecting pressurised oil at the inlet port.

11. The gas turbine engine according to claim 1 , wherein:

the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft;

the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and

the second core shaft is arranged to rotate at a different rotational speed than the first core shaft.