Hydraulic actuation system

1. A hydraulic actuation system for an aircraft, the hydraulic actuation system comprising:

an actuator (A);

a primary actuation arrangement to provide hydraulic fluid to control the actuator (A), wherein the hydraulic actuation system is configured to detect a fault in the actuator (A); and

a secondary actuation arrangement, wherein, in operation, the hydraulic actuation system is configured to switch operation from the primary actuation arrangement to the secondary actuation arrangement to provide hydraulic fluid to control the actuator (A) in response to a detection of a fault in the actuator (A);

wherein the primary actuation arrangement is provided on a static part of a nacelle and the secondary actuation arrangement is provided on a rotating part of a nacelle.

2. The hydraulic actuation system of any claim 1 , wherein the actuator (A) further comprises:

a first chamber and a second chamber, and wherein the primary actuation arrangement controls the hydraulic fluid in the first chamber and the second chamber; and

a third chamber, wherein the secondary actuation arrangement controls the hydraulic fluid provided in the third chamber.

3. The hydraulic system of claim 2 , wherein the first chamber is configured to decrease pitch of a propeller blade of the aircraft;

wherein the second chamber is configured to increase pitch of the propeller blade of the aircraft; and

wherein the third chamber is configured to increase pitch of the propeller blade of the aircraft.

4. The hydraulic actuation system of claim 1 , wherein the primary actuation arrangement includes at least one pressure sensor to detect a fault in the actuator (A).

5. The hydraulic actuation system of claim 1 , wherein the primary actuation arrangement includes an electric pump, a main pump, a by-pass valve and a primary electro-hydraulic servovalve to control the actuator (A).

6. The hydraulic actuation system of claim 1 , wherein the secondary actuation arrangement includes a signal module to provide a signal to a secondary electro-hydraulic servovalve to control the actuator (A).

7. The hydraulic actuation system of claim 1 , wherein the actuator (A) further comprises at least one seal.

8. A nacelle for an aircraft, comprising:

a rotating part;

a static part; and

the hydraulic actuation system as claimed in claim 1 ;

wherein the primary actuation arrangement is provided in or on the static part and the secondary actuation arrangement is provided in or on the rotating part.

9. A method comprising:

providing an actuator (A);

providing hydraulic fluid to control the actuator (A) with a primary actuation arrangement;

detecting a fault in the actuator (A) by an hydraulic actuation system; and

switching operation from the primary actuation arrangement to a second actuation arrangement to provide hydraulic fluid to the actuator (A) with the secondary actuation arrangement in response to the detected fault in the actuator (A);

wherein the primary actuation arrangement is provided on a static part of a nacelle and the secondary actuation arrangement is provided on a rotating part of a nacelle.

10. The method of claim 9 , wherein the actuator (A) comprises:

a first chamber and a second chamber, wherein the primary actuation arrangement controls the hydraulic fluid in the first chamber and the second chamber; and

a third chamber, wherein the secondary actuation arrangement controls the hydraulic fluid provided in the third chamber.

11. The method claim 9 , wherein the primary actuation arrangement includes an electric pump, a main pump, a by-pass valve and a primary electro-hydraulic servovalve to control the actuator (A).

12. The method of claim 11 , wherein the secondary actuation arrangement includes a signal module to provide a signal to a secondary electro-hydraulic servovalve to control the actuator (A).

13. The method of claim 11 , wherein the actuator (A) further comprises at least one seal.