METHOD AND SYSTEM FOR MONITORING THE PERFORMANCE OF AN AIRCRAFT HYDRAULIC SYSTEM

Abstract

A method for monitoring the performance of an aircraft hydraulic system is proposed. The method comprises: collecting temperature values ​​of a hydraulic fluid in the hydraulic system, measured by a sensor during a flight of rank I of the aircraft; determining the maximum temperature value of rank I, denoted Imax, among the collected values; calculating at least one temperature change indicator as a function of Imax; if this temperature change indicator is greater than a first threshold, calculating a temperature increase indicator, denoted Imax, as a function of a comparison between Imax and a reference value; and triggering an alert if Imax is greater than a second threshold. Thus, it is possible to monitor the performance of this hydraulic system in a simple and reliable manner, allowing for the anticipation of potential operational interruptions by triggering maintenance alerts well in advance. Figure to be published with the abbreviation: Fig. 3

Description

Title of the invention: METHOD AND SYSTEM FOR MONITORING THE PERFORMANCE OF AN AIRCRAFT HYDRAULIC SYSTEM technical field

[0001] The field of the invention is that of health monitoring and aircraft maintenance.

[0002] More specifically, the present invention relates to a method for monitoring the performance of an aircraft hydraulic system.

[0003] When the aircraft includes several hydraulic systems (which is generally the case), the proposed solution can be implemented for each hydraulic system.

[0004] The present invention also relates to: a monitoring system adapted to the implementation of such a monitoring method; a computer program product and a storage medium enabling the implementation of such a monitoring method; and a maintenance method based on such a monitoring method. STATE OF PRIOR ART

[0005] Aircraft are subjected to extreme conditions when they are in the air, particularly in terms of variations in temperature, pressure and speed. The performance of their components must be regularly checked to ensure their proper functioning.

[0006] Preventive or predictive maintenance consists of carrying out checks and repairs before a breakdown occurs.

[0007] In the field of aeronautics, maintenance makes it possible in particular to improve the availability and performance of an aircraft by avoiding its immobilization on the ground (AOG, for "Aircraft On Ground" in English), and to reduce maintenance costs by making it possible to identify in advance maintenance operations based on the actual performance of the aircraft.

[0008] Monitoring the aircraft's health status for maintenance purposes includes collecting technical data from the moment the aircraft is powered on, then during flight and until it is stopped. The data thus collected is used in particular to calculate the various indicators on which maintenance is based, and therefore the scheduling of maintenance operations.

[0009] The use of the data can take place during the flight (this is referred to as in-flight health monitoring) and / or after the flight (for example, if the volume of data to be processed requires computing resources). higher). Calculations using the collected data can therefore be performed in the aircraft and / or in one or more ground-based devices. In the latter case, the ground-based devices (computers) receive the data collected in the aircraft, either in real time or with a delay.

[0010] Observing the condition of an aircraft over several flights allows ground personnel to make decisions and plan maintenance operations in advance, thus saving valuable execution time. Ground personnel can then make appropriate decisions based on criticality, logistics, and upcoming maintenance checks, and prepare repairs and replacements in advance.

[0011] As part of this maintenance, there is a particular need to monitor the performance of an aircraft's hydraulic system. For this, a reliable and easy-to-implement solution is required, one that allows for the anticipation of potential operational interruptions by raising maintenance alerts sufficiently in advance. Description of the invention

[0012] A method is proposed for monitoring the performance of a hydraulic system of an aircraft, the aircraft being equipped with a temperature sensor measuring temperature values ​​of a hydraulic fluid of the hydraulic system, the method being implemented by a monitoring system comprising electronic circuitry, the method comprising, for a given flight, of rank i, of the aircraft:

[0013] - collect temperature values ​​measured by the temperature sensor during the first-rank flight;

[0014] - determine a maximum temperature value of rank *, denoted T,)tax^ defined as the maximum value among the temperature values ​​collected during the z-rank flight;

[0015] - calculate at least one temperature evolution indicator as a function of the value of maximum temperature of rank i, Tmax j;

[0016] - if said at least one temperature evolution indicator is greater than one First predetermined threshold, calculate a temperature increase indicator, denoted as a function of a comparison between the maximum temperature value of rank z, Ttnaxj, and a reference value, denoted P; and

[0017] - trigger a first alert if the temperature increase indicator is above a second predetermined threshold.

[0018] Thus, it is possible to monitor the performance of an aircraft hydraulic system, thanks to a solution that is reliable and simple to implement. work, and which makes it possible to anticipate possible interruptions in operation by raising maintenance alerts sufficiently in advance.

[0019] According to a particular embodiment, the method further comprises: calculating an average maximum temperature value of rank, denoted T™, defined as a moving average of the maximum temperature value over a first flight window including flight rank 1 and the 5 preceding flights of ranks − to i - 1. In addition, the calculation of said at least one temperature evolution indicator and the calculation of the temperature increase indicator are carried out using the average maximum temperature value of rank, T®, instead of the maximum temperature value of rank, Tmaxi.

[0020] According to a particular embodiment, said at least one temperature change indicator belongs to the group comprising: • a first indicator of temperature evolution, denoted as a function of a comparison between the average maximum temperature value of rank i, T®, and an average maximum temperature value of rank i-®, denoted Tw; and • a second temperature evolution indicator, denoted function of a comparison between the average maximum temperature value of rank », T®, and another average maximum temperature value of rank », denoted , defined as a moving average of the maximum temperature value over a second flight window including the flight of rank », and the previous W flights of ranks i - W to i -1, with II > w.

[0021] According to a particular embodiment, the first temperature evolution indicator is defined as follows: . T“ - . — œ

[0022] According to a particular embodiment, the second temperature evolution indicator is defined as follows: (t“. th)3 , with Varmax ) the variance ai~ of a variable Tmax taking the values ​​Tmaxj with i {i - (0, .,., € i - 2, i -1, i ].

[0023] According to a particular embodiment, the method further comprises: correcting the collected temperature values ​​according to the ambient air temperature measured outside the aircraft and the aircraft altitude. In addition, the determination of the maximum temperature value of rank ", denoted Tl)mx^ is carried out among the temperature values ​​collected during the flight of rank " and corrected.

[0024] According to a particular embodiment, the reference value P is calculated as follows:

[0025] - if said at least one temperature evolution indicator is greater than the first predetermined threshold for the given flight of rank i and if there is a previous flight for which said at least one temperature evolution indicator was detected as exceeding the first predetermined threshold, the reference value P is the average value of the collected and corrected temperatures, from the previous flight for which said at least one temperature evolution indicator was detected as exceeding the first predetermined threshold, up to flight of rank i; and

[0026] - if said at least one temperature evolution indicator is greater than the first predetermined threshold for the given flight of rank 1 and if there is no previous flight for which said at least one temperature evolution indicator was detected above the first predetermined threshold, the reference value P is the average value of the temperatures collected and corrected, over a predetermined number of flights preceding the flight of rank.

[0027] According to a particular embodiment, the temperature increase indicator is defined as follows: Tf-fi , . a . = — x 100

[0028] According to a particular embodiment, the method further comprises: triggering a second alert if the average maximum temperature value of rank", T®, is greater than a third predetermined threshold.

[0029] According to a particular embodiment, the temperature increase indicator is calculated if said at least one temperature evolution indicator is greater than the first predetermined threshold and if the average maximum temperature value of rank 4 T® is greater than a fourth threshold.

[0030] A computer program product is also proposed, comprising instructions leading to the execution, by a processor, of the process mentioned above according to any one of its embodiments, when said instructions are executed by the processor.

[0031] A storage medium is also proposed, storing such instructions.

[0032] A system for monitoring the performance of a system is also proposed. hydraulics of an aircraft, the aircraft being equipped with a temperature sensor measuring temperature values ​​of a hydraulic fluid of the hydraulic system, the monitoring system comprising electronic circuitry configured to implement, for a given flight, of rank i, of the aircraft:

[0033] - collect temperature values ​​measured by the temperature sensor during the flight of rank";

[0034] - determine a maximum temperature value of rank », denoted Tnutx ^ defined as the maximum value among the temperature values ​​collected during the flight rank”;

[0035] - calculate at least one temperature evolution indicator as a function of the value of maximum temperature of rank 4 Tf;

[0036] - if said at least one temperature evolution indicator is greater than one First predetermined threshold, calculate a temperature increase indicator, denoted %, based on a comparison between the maximum temperature value of rank \ Tf, and a reference value, denoted fi; and

[0037] - trigger an alert if the temperature increase indicator, ai, is above a second predetermined threshold.

[0038] A method for maintaining an aircraft hydraulic system is also proposed, the method comprising:

[0039] - to execute the process mentioned above according to any one of its modes of implementation, to monitor the performance of the hydraulic system; and

[0040] - in the event of a system performance alert being triggered hydraulics, perform at least one maintenance operation on the hydraulic system. Brief description of the drawings

[0041] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of at least one exemplary embodiment, said description being made in relation to the accompanying drawings, among which:

[0042] [Fig-1] schematically illustrates, in side view, an aircraft equipped with a system of monitoring the performance of an aircraft's hydraulic system;

[0043] [Fig.2] schematically illustrates an example of the hardware architecture of the system of monitoring the performance of a hydraulic system;

[0044] [Fig.3] schematically illustrates an example of an algorithm for monitoring the performance of a hydraulic system; and

[0045] [Fig.4] schematically illustrates an example of a maintenance algorithm for a aircraft hydraulic system.

[0046] DETAILED DESCRIPTION OF IMPROVEMENTS

[0047] An aircraft generally comprises several independent hydraulic systems, also called hydraulic circuits. These are used to actuate virtually all the moving parts necessary for flight, such as the landing gear, brakes, flaps, spoilers, flight controls, etc. Each hydraulic system has its own reservoir, containing pressurized hydraulic fluid used to transmit power and force from one point to another. The simplified typical path of the hydraulic fluid is as follows: it passes from the reservoir to a high-pressure pump, then successively through a high-pressure filter, into a distributor and in the auxiliary system (cylinder, hydraulic motor...). For the return, it passes through a low-pressure filter before returning to the reservoir.

[0048] To comply with certification standards aimed at minimizing the consequences of a failure, an aircraft typically has three hydraulic systems (circuits), designed so that the crew can maintain control of the aircraft in the event of a failure of one of them (or even in the event of a double failure). Each of these three hydraulic systems is generally designated by a distinct color: BLUE, GREEN, or YELLOW.

[0049] For each hydraulic system, the aircraft is equipped with a temperature sensor that measures the temperature of the hydraulic fluid in the reservoir. If the measured temperature exceeds a predetermined threshold (e.g., 98°C), an ECAM (Electronic Centralized Aircraft Monitor) alarm of the type “HYD X RSVR OVHT” is generated for the crew to indicate reservoir overheating (where X equals B, G, or Y to specify the color of the hydraulic system concerned). There are several possible causes of overheating, including: pump malfunction, internal leak, valve problem, wiring problem, etc. In practice, if two (or even just one) of the three hydraulic systems overheat, the crew makes a no-go decision.

[0050] The present invention aims to prevent such overheating for each hydraulic system, and therefore the corresponding ECAM alarm, and thus avoid a no-takeoff decision.

[0051] Since the proposed solution can be implemented for each of the hydraulic systems, a single hydraulic system is referred to generically in the rest of the description.

[0052] Fig. 1 schematically illustrates, in side view, an aircraft 100 equipped with a hydraulic system 101 and a system 200 for monitoring the performance of this hydraulic system.

[0053] As detailed below, the hydraulic system performance monitoring system 200 can trigger an alert (for example, by displaying information and / or sending a message to a maintenance service) if a triggering condition is met. Furthermore, as also detailed below, the triggering of an alert related to the hydraulic system can be followed by at least one maintenance operation on that hydraulic system (for example, the repair or replacement of one or more components of the hydraulic system).

[0054] In a particular implementation, the hydraulic system performance monitoring system 200 is an embedded electronic device. For example, it is part of the electronic circuitry of the aircraft avionics 100. Preferably, it is integrated into an aircraft computer 100.

[0055] In one variant, the hydraulic system performance monitoring system 200 is not carried on board the aircraft 100 but is located on the ground.

[0056] In another embodiment, the hydraulic system performance monitoring system 200 comprises a first part that is installed in the aircraft 100 and a second part that is located on the ground. Thus, the calculations and the triggering of alerts can be distributed between the two parts of the system 101.

[0057] In another variant, at least one 200 hydraulic system performance monitoring system is carried on board the aircraft and at least one 200 hydraulic system performance monitoring system is installed on the ground.

[0058] Fig. 2 schematically illustrates an example of the hardware architecture of the hydraulic system performance monitoring system 200, which includes, connected by a communication bus 210: a processor or CPU (Central Processing Unit) 201; a RAM (Random Access Memory) 202; a ROM (Read Only Memory) 203, for example a Flash memory; a data storage device, such as a HDD (Hard Disk Drive), or a storage media reader, such as an SD (Secure Digital) card reader 204; at least one communication interface 205 allowing the monitoring system 200 to interact with the avionics of the aircraft 100.

[0059] The processor 201 is capable of executing instructions loaded into RAM 202 from ROM 203, external memory (not shown), a storage medium such as an SD card, or a communication network (not shown). When the monitoring system 200 is powered on, the processor 201 is capable of reading instructions from RAM 202 and executing them. These instructions form a computer program causing the processor 201 to implement the behaviors, steps, and algorithm described herein.

[0060] All or part of the behaviors, steps, and algorithms described herein can thus be implemented in software form by executing a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor) or a microcontroller, or be implemented in hardware form by a dedicated machine or component (chip) or a dedicated set of components (chipset), such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). Generally speaking, the 200 monitoring system comprises electronic circuitry arranged and configured to implement the behaviors, steps, and algorithms described herein.

[0061] Figure 3 schematically illustrates an example of an algorithm for monitoring the performance of an aircraft hydraulic system. The algorithm (method) is implemented by the monitoring system 200 discussed above in relation to the [Fig. 1] and 2. As already mentioned above, the aircraft is equipped with a temperature sensor measuring temperature values ​​of a hydraulic fluid in the hydraulic system (for example, the temperature in the reservoir of this hydraulic system).

[0062] The algorithm is executed for each of the successive flights of the aircraft. We now detail the steps of the algorithm, considering an execution for a given flight, of rank z, of the aircraft.

[0063] In a step 301, the monitoring system 200 collects temperature values ​​(of the hydraulic fluid of the monitored hydraulic system) measured by the temperature sensor during flight rank i of the aircraft. In one embodiment, the collection is limited to one or more phases of the flight, for example the cruise phase (phase 6 (“Cruise”) in the case of a flight divided into ten phases).

[0064] In step 302, the monitoring system 200 corrects the collected temperature values ​​based on the ambient air temperature (SAT for "Static Air Temperature") measured outside the aircraft and the aircraft's altitude. This correction aims, in particular, to eliminate the seasonality of the measurements.

[0065] In a step 303, the monitoring system 200 determines a maximum temperature value of rank 1, denoted Tllulxj, defined as the maximum value among the temperature values ​​collected during the flight of rank ' and corrected.

[0066] In step 304, the monitoring system 200 calculates a mean maximum temperature value of rank 6, denoted T®, defined as a moving average of the maximum temperature value over a first flight window comprising flight rank 1 and the preceding flights of ranks i - c to i - 1 (for example, c = 10). Thus, the mean maximum temperature value of rank 1, Tj0, can be expressed according to the following equation:

[0067] Tœ__l_y* T li — maxj

[0068] In step 305, the monitoring system 200 calculates at least one temperature evolution indicator as a function of the average maximum temperature value of rank T™. In a particular embodiment, the monitoring system 200 calculates two temperature evolution indicators, Az and Az, which are detailed below. In a variant, the monitoring system 200 calculates only one of these two temperature evolution indicators.

[0069] The indicator A,- is a function of a comparison between the average maximum temperature value of rank Σ, T®, and an average maximum temperature value of rank i - ®, denoted T® r. In a particular implementation, the indicator A(- is defined as follows:

[0070] A

[0071] The indicator is a function of a comparison between the average maximum temperature value of rank ", T®, and another average maximum temperature value of rank ", denoted tP', defined as a moving average of the maximum temperature value over a second flight window comprising the flight of rank i and the preceding VL flights of ranks iW to -1, with W>w (for example, W - 5*w). In a particular implementation, the indicator ai is defined as follows:

[0072] (T®-T(w)3 Vara(Tmgx)

[0073] with VarTmax ) the variance of a variable Tfnax taking the values ​​Tltiaxj with je {f - co, ..., € i - 2, i -1, i}.

[0074] Indicator A indicates a rapid (abrupt) temperature change, which occurs, for example, when a pump in the hydraulic system stops working. Indicator B indicates a slow (gradual) temperature change, which occurs, for example, when there is a leak in the hydraulic system. Indicators A and B are therefore complementary.

[0075] In a step 306, the monitoring system 200 checks whether the average value of maximum rank i temperature, T®, is greater than a predetermined threshold XI (for example, XI = 65°C).

[0076] If the answer to the test in step 306 is "yes", the monitoring system 200 proceeds to step 307 in which it triggers an alert (for example, the display of information and / or the sending of a message to a maintenance service), then it proceeds to the final step 314.

[0077] If the test in step 306 fails, the monitoring system 200 proceeds to step 308, in which it checks whether the indicator is above a predetermined threshold Z (for example, Z = 20). In a particular implementation of step 308, the monitoring system 200 further checks whether another condition is met, namely whether the average value of the maximum temperature of rank i, T®, is above a predetermined threshold X2 (for example, X2 = 55°C).

[0078] If the answer to the test (or double test in the particular implementation) of step 308 is "yes", the monitoring system 200 proceeds to step 310 described below.

[0079] If the test in step 308 fails, the monitoring system 200 proceeds to step 309, in which it checks whether the indicator A,- is greater than a predetermined threshold Y (for example, Y = 1). In a particular implementation of step 309, the monitoring system 200 further checks whether another condition is met, namely whether the average maximum temperature value of rank I, T®, is greater than a predetermined threshold X3 (for example, X3 = 50°C).

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[0091] If the test (or double test in the specific implementation) in step 309 is successful, monitoring system 200 proceeds to step 310, described below. If the test in step 309 is unsuccessful, monitoring system 200 proceeds to the final step, 314. In step 310, the monitoring system 200 calculates a reference value P as follows: - if there is a previous flight for which one of the indicators was detected as being above its associated threshold (Y and Z respectively), the reference value P is the average value of the temperatures collected and corrected, from that previous flight up to flight i; and - If there is no previous flight for which one of the indicators \ and was detected as being above its associated threshold (Y and Z respectively), the reference value P is the average value of the collected and corrected temperatures, over a predetermined number (for example 75) of flights preceding flight h In step 311, the monitoring system calculates a temperature rise indicator, denoted at, based on a comparison between the mean maximum temperature value of rank *, T[°, and the reference value P. In a particular implementation, the indicator ai is defined as follows (in order to be expressed as a percentage): T® R = ~y~ x 100 In a step 312, the monitoring system 200 checks whether the indicator ai is above a predetermined threshold S (for example, S = 5%). If the answer to the test in step 312 is "yes", the monitoring system 200 proceeds to step 313 in which it triggers an alert (for example, displaying information and / or sending a message to a maintenance service), then it proceeds to the final step 314. If the answer to the test in step 312 is "no", the monitoring system 200 proceeds directly to the final step 314. Figure 4 schematically illustrates an example of an algorithm for maintaining an aircraft hydraulic system. In a step 401, the monitoring system 200 executes a performance monitoring algorithm for a hydraulic system, for example in the particular embodiment described above (see the description of [Fig.3]). If an alert was triggered at the end of step 401 (result "yes" in test step 402), at least one maintenance operation is carried out on the given electromechanical switch (step 403).

Claims

Demands

1. A method for monitoring the performance of a hydraulic system (101) of an aircraft (100), the aircraft being equipped with a temperature sensor measuring temperature values ​​of a hydraulic fluid of the hydraulic system, the method being implemented by a monitoring system (200) comprising electronic circuitry, the method comprising, for a given flight, of rank 1, of the aircraft: - collecting (301) temperature values ​​measured by the temperature sensor during the flight of rank 1; - determining (303) a maximum temperature value of rank z, denoted T maxj, defined as the maximum value among the temperature values ​​collected during the flight of rank z; - calculating (305) at least one temperature evolution indicator as a function of the maximum temperature value of rank 1, Tnwx;- if said at least one temperature evolution indicator is greater than a first predetermined threshold, calculate (311) a temperature increase indicator, denoted ai, as a function of a comparison between the maximum temperature value of rank i, Tmaxj, and a reference value, denoted P; and - trigger (313) a first alert if the temperature increase indicator, ai, is greater than a second predetermined threshold.

2. A method according to claim 1, further comprising: - calculating (304) an average maximum temperature value of rank z, denoted T®, defined as a moving average of the maximum temperature value over a first flight window comprising the flight of rank i and the preceding flights of ranks i - to to i - 1; and wherein the calculation (305) of said at least one temperature evolution indicator and the calculation (311) of the temperature increase indicator are carried out using the average maximum temperature value of rank z, T®, instead of the maximum temperature value of rank i, T,^j.

3. A method according to claim 2, wherein said at least one temperature change indicator belongs to the group comprising: • a first temperature evolution indicator, denoted A', function of a comparison between the average maximum temperature value of rank t T®, and an average maximum temperature value of rank i - denoted T^, ; and • a second temperature evolution indicator, denoted function of a comparison between the average maximum temperature value of rank ', T®, and another average maximum temperature value of rank i, denoted T?y, defined as a moving average of the maximum temperature value over a second flight window including the flight of rank 1 and the previous VF flights of ranks iW to i-1, with VF > w.

4. A method according to claim 3, wherein the first temperature evolution indicator is defined as follows: .

5. Method according to claim 3, wherein the second temperature evolution indicator is defined as follows: (t?\ t1*)3 , Var^Tmtlx} with Vttra(Tmax) the variance of a variable Tf^- taking the values ​​Tmaxj with je {i-û)- ..., € i- 2. i-1, i}.

6. A method according to any one of claims 1 to 5, further comprising: - correcting (302) the temperature values ​​collected as a function of the ambient air temperature measured outside the aircraft and the altitude of the aircraft, and wherein the determination (303) of the maximum temperature value of rank ', denoted Tmaxj, is carried out among the temperature values ​​collected during the flight of rank i and corrected.

7. A method according to claim 6, wherein the reference value fi is calculated (310) as follows: - if said at least one temperature evolution indicator is greater than the first predetermined threshold for the given flight of rank 1 and if there is a previous flight for which said at least one temperature evolution indicator was detected to be greater than the first predetermined threshold, the reference value fi is the average value of the temperatures collected and corrected, since the previous flight for which said at least one temperature evolution indicator was detected above the first predetermined threshold, up to flight of rank '; and - if said at least one temperature evolution indicator is above the first predetermined threshold for the given flight of rank 1 and if there is no previous flight for which said at least one temperature evolution indicator was detected above the first predetermined threshold, the reference value P is the average value of the collected and corrected temperatures, over a predetermined number of flights preceding flight of rank h

8. A method according to any one of claims 1 to 7, wherein the temperature rise indicator is defined as follows: a- = -7- x 100 i [J

9. A method according to any one of claims 2 to 8, further comprising: - triggering (307) a second alert if the average maximum temperature value of rank T?', is greater than a third predetermined threshold.

10. A method according to any one of claims 1 to 9, wherein the temperature increase indicator, ai, is calculated if said at least one temperature evolution indicator is greater than the first predetermined threshold and if the average maximum temperature value of rank T®, is greater than a fourth threshold.

11. Product computer program, comprising instructions causing a processor (201) to execute the method according to any one of claims 1 to 10, when said instructions are executed by the processor.

12. Storage medium (203), storing a computer program comprising instructions causing a processor (201) to execute the method according to any one of claims 1 to 10, when said instructions are read and executed by the processor.

13. System (200) for monitoring the performance of a hydraulic system (101) of an aircraft (100), the aircraft being equipped with a temperature sensor measuring temperature values ​​of a hydraulic fluid of the hydraulic system, the monitoring system comprising electronic circuitry configured to implement, for a given flight, of rank *, of the aircraft: - collect (301) temperature values ​​measured by the temperature sensor during the flight of rank '; - determine (303) a maximum temperature value of rank ', denoted Tmax i^ defined as the maximum value among the temperature values ​​collected during the flight of rank *; - calculate (305) at least one temperature change indicator as a function of the maximum temperature value of rank £, Tf; - if said at least one temperature change indicator is greater than a first predetermined threshold, calculate (311) a temperature increase indicator, denoted ai, as a function of a comparison between the maximum temperature value of rank z, T®, and a reference value, denoted P; and - trigger (313) an alert if the temperature increase indicator, ai, is greater than a second predetermined threshold.

14. A method for maintaining a hydraulic system (101) of an aircraft (100), the method comprising: - performing (401) the method according to any one of claims 1 to 10, to monitor the performance of the hydraulic system; and - in the event of triggering (402) an alert relating to the performance of the hydraulic system, performing (403) at least one maintenance operation on the hydraulic system.

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