Method for determining a duration of movement for a starter air valve of a turbine engine

1. A method of determining a duration of a movement of a starter air valve of a turbine engine, the starter air valve being configured to regulate the passage of a flow of pressurized air from an upstream side to a downstream side of a pipework, where the downstream side of the pipework is connected to a pneumatic starter of the turbine engine, the method comprising:

determining an instant of initiation and an instant of completion of a movement of the starter air valve during a movement phase of the starter air valve;

determining the duration by subtracting the instant of initiation from the instant of completion;

calculating a difference between the duration and a theoretical value of the duration;

wherein the instant of initiation and the instant of the completion are each determined by:

periodically measuring a pressure within the upstream side of the pipework, during the movement phase,

obtaining a characteristic quantity representing a change in pressure as a function of time, wherein from a recording of periodic measurements of the pressure:

a median time interval is identified during which a difference between two successive pressure measurements exceeds, in absolute terms, a predetermined threshold,

a first linear regression line is calculated over the median time interval,

a second linear regression line and a third linear regression line are calculated over time intervals which respectively precede and follow the median time interval, and

the instant of initiation and the instant of completion are calculated as being a point of intersection between the first linear regression line and the second linear regression line, and a point of intersection between the second linear regression line and the third linear regression line, respectively,

determining a representative instant at which the characteristic quantity shows a variation representative of an initiation or of a completion of the movement,

determining the instant of initiation or the instant of completion as being the representative instant.

2. The method according to claim 1 , wherein the characteristic quantity is a derivative of the change in pressure, and the representative instant at which the derivative exhibits the variation representative of the initiation or of the completion of the movement is determined as a corresponding instant at which the derivative changes from one of: a null value to a non-null value, or vice versa.

3. The method according to claim 1 , wherein the characteristic quantity is a series of linear regression lines calculated over successive intervals of measured values of the pressure, the series of linear regression lines comprising at least the first linear regression line, the second linear regression line, and the third linear regression line.

4. The method according to claim 1 , further comprising:

triggering a first alarm when the difference is greater than a duration threshold.

5. The method according to claim 1 , further comprising:

determining a pressure difference within the upstream side of the pipework, between the instant of initiation and the instant of completion; and

calculating a difference between the pressure difference and an expected value.

6. The method according to claim 5 , further comprising:

triggering a first alarm when the difference between the pressure difference and the expected value is greater than a pressure threshold.

7. A computer program comprising a set of instructions which, when executed by a turbine engine's computer, causes the implementation of a method according to claim 1 .

8. The method according to claim 1 , wherein the pressure is periodically measured using a pressure sensor placed at an outlet of a compressor.

9. The method according to claim 1 , wherein the pressure sensor is located in a tail of an aircraft.

10. The method according to claim 1 , wherein the characteristic quantity comprises a derivative of the pressure, the method further comprising:

obtaining a filtered derivative, wherein the representative instant is associated with the filtered derivative.

11. The method according to claim 1 , wherein the theoretical value is indicated by a manufacturer of the starter air valve.

12. The method according to claim 1 , further comprising:

constructing a model of the pressure as a function of one or more parameters using a learning phase; and

determining, from the model, the theoretical value based on at least one start-up value associated with the one or more parameters.