HK1202322B - Method and apparatus for monitoring turbine efficiency of aircraft auxiliary power unit - Google Patents

Abstract

The present invention relates to a method and device for monitoring performance of an auxiliary power unit (APU) turbine efficiency of an aircraft. The method comprises: obtaining APU messages at multiple time points within a period; obtaining APU startup parameters including at least a rotation speed at a peak of EGT according to the APU messages; calculating a percentage NPA of the rotation speed when the exhausting gas temperature EGT reaches its peak at the APU startup stage relative to the rotation speed in the APU normal operation; calculating the average of the NPA within the period; and determining which of the stable, decline and failure phases the APU turbine efficiency is in according to the average of the NPA.

Description

Method and device for monitoring turbine efficiency of auxiliary power unit of airplane

Technical Field

The present invention relates to monitoring performance of aircraft components, and more particularly, to a method and apparatus for monitoring turbine efficiency of an aircraft auxiliary power unit.

Background

An airborne auxiliary power unit (AirborneAuxiliaryPowerUnit), called auxiliary power unit APU for short, is a small turbine engine installed at the tail of an airplane. The main function of the APU is to provide power and air, and there are also a small number of APUs that can provide additional thrust to the aircraft. Specifically, the APU provides power to start the main engine before the aircraft takes off from the ground, so that ground electric and air source vehicles are not needed to start the aircraft. On the ground, the APU also provides power and compressed air to ensure lighting and air conditioning in the passenger cabin and the cockpit. When the airplane takes off, the APU can be used as a standby power supply. After the aircraft lands, the APU still supplies power for illumination and air conditioning. The function of the APU determines the stability of its operation directly related to the flight cost and quality of service of the aircraft.

Since the APU is a turbine engine, turbine efficiency is an important indicator of APU performance. The prior art has no effective means for evaluating the turbine efficiency of the APU, and the performance of the APU cannot be evaluated. The present invention is a solution to this problem.

Disclosure of Invention

In view of the above technical problems in the prior art, according to an aspect of the present invention, a method for detecting the turbine efficiency of an APU of an aircraft auxiliary power unit is provided, including: acquiring APU messages at a plurality of time points in a time period; acquiring starting parameters of the APU according to the APU message, wherein the starting parameters at least comprise peak EGT rotating speed; calculating the ratio NPA of the rotating speed at the exhaust temperature peak value when the APU is started relative to the rotating speed when the APU normally operates; calculating an average of the NPAs over the time period; and determining that the APU turbine efficiency is in a stable period, a decline period or a fault period according to the average value of the NPA.

The method as described above, wherein the step of determining that the APU turbine efficiency is in a stationary period, a decline period, or a fault period comprises: determining that the APU turbine efficiency is in a decline period in response to the average of the NPAs over the time period approaching a first threshold value; and determining that the APU turbine efficiency is in a failure period in response to the average of the NPAs over the time period approaching a second threshold value.

The method as described above, wherein the first threshold value is about 35% for an APU of APS3200 type; the second threshold is approximately 32% and "close" is within approximately 1.5% of the gap.

The method as described above, wherein the first threshold value is about 45% for an APU of GTCP131-9 type A; the second threshold is approximately 40% and "close" is within approximately 2.5%.

The method as described above, wherein approximately 10-20 APU messages are acquired within the time period.

The method as described above, further comprising: performing linear or nonlinear fitting on all NPAs in the period of time, and linearly extrapolating the fitted result; determining that the turbine efficiency of the APU has entered a decay period if the intersection of the linear extrapolation result with the first threshold value is within about 1 month; and determining that the turbine efficiency of the APU has entered a failure period if the intersection of the result of the linear extrapolation and the second threshold value is within about 1 month.

The method as described above, further comprising: after linear or non-linear fitting, the confidence interval of the NPA is calculated.

The method as described above, further comprising: and according to the intersection point of the extrapolation result of the confidence interval and the first threshold value and the second threshold value.

The method as described above, further comprising: the efficiency of the APU is estimated to enter a time range of a decline period or a failure period.

The method as described above, further comprising: it is determined whether the peak EGTP of the exhaust temperature at the start of the APU is near the red line value.

The method as described above, further comprising: and determining whether the corrected peak value EGTP of the exhaust temperature at the starting time of the APU is close to a red line value or not, wherein the correction formula is as follows:

EGTP_COR=((EGTP+273.5)/THITA)-273.5；

wherein EGTP _ COR is the corrected EGTP, and EGTP is the uncorrected EGTP, THITA = e ^ (- ((AltValue × CoverFt)/1000)/((8.51 × (273.15+ TATValue))/(9.8 ^ 29))).

The method as described above, further comprising: it is determined that the start time STA is within a normal range.

According to another aspect of the invention, a device for detecting the turbine efficiency of an aircraft auxiliary power unit APU is provided, comprising: the message acquisition unit acquires an APU message in a time period; the message analysis unit is used for analyzing required APU starting parameters, and the starting parameters at least comprise peak value EGT rotating speed; and the performance detection unit is used for determining that the performance of the turbine efficiency of the APU is in a stable period, a decline period or a fault period according to the NPA.

According to another aspect of the invention, a device for detecting the turbine efficiency of an aircraft auxiliary power unit APU is provided, comprising: a processor; and a memory coupled to the processor, storing computer readable code; the computer readable code running on the processor to perform the steps of: acquiring an APU message in a time period; analyzing the APU starting parameters according to the message, wherein the starting parameters at least comprise peak value EGT rotating speed; and determining that the performance of the APU turbine efficiency is in a stationary period, a decay period or a fault period.

Drawings

Preferred embodiments of the present invention will now be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic structural diagram of an aircraft APU according to one embodiment of the present invention;

FIG. 2 shows a statistical trend graph of APU turbine efficiency;

FIG. 3 shows an example of an A13 message for airbus;

FIG. 4 illustrates a flow diagram of a method of monitoring APU turbine efficiency in accordance with one embodiment of the present invention;

FIG. 5 is a flow diagram of a method of monitoring APU turbine efficiency, in accordance with another embodiment of the present invention;

FIG. 6 is an example of APU turbine efficiency variation according to one embodiment of the invention; and

FIG. 7 is a schematic structural diagram of an aircraft auxiliary power unit APU turbine efficiency monitoring apparatus in accordance with an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof and in which is shown by way of illustration specific embodiments of the application. In the drawings, like numerals describe substantially similar components throughout the different views. Various specific embodiments of the present application are described in sufficient detail below to enable those skilled in the art to practice the teachings of the present application. It is to be understood that other embodiments may be utilized and structural, logical or electrical changes may be made to the embodiments of the present application.

FIG. 1 shows a schematic structural diagram of an aircraft APU in accordance with one embodiment of the present invention. As shown, the aircraft APU generally includes a power section 100, a load section 200, and an accessory section 300. The power part 100 mainly comprises a power compressor 110, a turbine assembly 120, an exhaust assembly 130 and the like; the load part 200 mainly includes a load compressor 210; the accessory portion 300 generally includes an accessory gearbox 310, a turbine efficiency 320, and a generator 330, among other things. The air flow entering from the air inlet is divided into two flows, one flow enters the power compressor 110 and the turbine assembly 120 and is mainly used for driving the APU to rotate, and then the air flow is discharged through the exhaust assembly 130; and the other stream enters the load compressor 210, which is pressurized by the load compressor and is used exclusively to produce compressed air for use by the aircraft. The inlet of the air flow is provided with a flow regulating valve (inlet guide vane), and the opening of the valve (vane) is regulated in real time according to the requirement of the airplane on compressed air so as to control the amount of air entering the load compressor.

When the starting speed of the APU is greater than the ignition threshold speed, the APU starts to supply oil, and the turbine of the APU accelerates under the power of the starter and the gas driven turbine. For example, for an APU type APS3200, the fuel supply is started when the rotation speed of the APU is 5% of the normal rotation speed; for the GTCP131-9A type APU, the oil supply is initiated when the APU rotates at 7% of normal speed. After the start of the fuel supply, the inside of the combustion chamber starts to shift from a lean state to a rich state, and the temperature of the combustion chamber is also increasing. In the starting stage of the APU starting, the front-end compressor has small air supply amount due to low rotating speed, and heat accumulation is easily caused, so that the highest exhaust temperature point appears, and the peak value EGTP of the exhaust temperature in the starting stage is reached. Along with the increase of the integral rotating speed of the turbine, the rich state of the combustion chamber is gradually changed into normal, the temperature of the combustion chamber is reduced, and the APU finishes the starting.

The inventors of the present application have found that when the turbine efficiency of the APU is low, the turbine speed will be relatively low when the peak of the exhaust gas temperature EGT, i.e. the highest temperature, is reached during the start-up phase. This is because the turbine efficiency is low and the rich condition is advanced. For example, for an APU of APS3200 type, the turbine performance degradation of the APU has been shown to be severe if the rotational speed at which the maximum exhaust temperature EGTP occurs during the start-up phase is only 32% of the rotational speed at which the APU is operating normally. Similarly, for the APU of GTCP131-9A type, if the rotating speed when the highest exhaust temperature EGTP appears in the starting phase reaches 40% of the rotating speed when the APU normally works, the turbine performance degradation of the APU is serious.

The inventors of the present application have further found that the performance variation of APU turbine efficiency follows a certain law: turbine efficiency is more stable during early and mid-stages of use, and performance degradation occurs during late stages until failure.

FIG. 2 is a schematic diagram of an APU turbine efficiency variation curve. As can be seen from the figure, the decay index gradually increases as the turbine efficiency of the aircraft APU gradually degrades with increasing usage time. When the decay index of the turbine efficiency of the APU is stable, the performance of the APU is in a stable period; when the performance degradation of the turbine efficiency of the APU is gradually accelerated, the performance of the APU enters a degradation period; when a certain threshold value is exceeded, the performance of the system enters a failure period, and a failure can occur at any time. When the turbine efficiency of the APU enters a fault period, the use of the APU is influenced, and adverse consequences are generated on the service quality and the flight safety; and is easy to cause non-planned maintenance, resulting in flight delay and flight stop.

The performance of the turbine efficiency of an aircraft APU can be characterized by the ratio NPA of the turbine speed at which the exhaust temperature EGT reaches the peak EGTP at the start-up of the APU relative to the speed at which the APU is operating normally.

There is no means in the prior art to detect whether APU turbine efficiency enters a decline period. And certain embodiments of the present invention may implement such detection. The following benefits are achieved for the detection of the decline period: when the APU turbine efficiency is in the decline period, the probability of failure is still very low. If the airplane is selected to be overhauled at the moment, the flight safety and the service quality can be guaranteed. At the moment, the airline company can timely arrange the maintenance of the aircraft, so that the unscheduled maintenance is avoided, and the delay of the aircraft is reduced. And meanwhile, the waste of maintenance cost caused by maintenance according to a fixed time limit is avoided.

Various methods may be used to obtain the NPA. For example, since each type of APU rotates at a constant rate during normal operation, NPA can be calculated by obtaining the peak EGT speed during the start-up phase. The peak EGT speed data is obtained from data stored in the aircraft black box FDR or the fast access recorder QAR.

The data can be conveniently acquired through a data system provided by an aircraft manufacturer, and ground real-time detection is realized. For example, both the aircraft aeronautical navigation system (acms) system and the aircraft health monitor (ahm) system of boeing corporation can monitor the operation data of the aircraft in real time, and automatically generate a message containing a series of data information when a certain trigger condition is met.

According to an embodiment of the present invention, the relevant operating data of the APU may be acquired by an aircraft data system (e.g., ACMS or AHM system) and embodied in the generated relevant message. Such message information may be transmitted to the ground through an aircraft communication addressing and reporting system (acarsair communication addressing and reporting system) system and further distributed to servers of different airlines. According to an embodiment of the present invention, the APU message may also be transmitted through a communication device or system of an aeronautical telecommunications network (aviation electrical network).

In fact, for the existing air data system, performance monitoring of the APU is an existing project, so that a corresponding APU message can be automatically generated and transmitted to the ground through ACARS or ATN. However, these monitored data are not used for the decay period detection of the APU performance. For example, the A13 message of airbus, i.e. (APUMES/IDLEREPORT), or the APU message of Boeing is an example of such an APU message. In the following embodiments, a message a13 of airbus is taken as an example for explanation. The Boeing APU messages are processed similarly.

Fig. 3 shows an example of a13 message for airbus. As shown in the figure, the a13 message mainly includes 4 pieces of information, which are: the system comprises a header, APU resume information, operating parameters for starting an aircraft engine and APU starting parameters.

The header consists of CC and C1 sections and mainly comprises flight information of the airplane, a message generation section stage, a bleed valve state, total temperature (namely outside temperature) and other information. The APU resume information is composed of section E1 and includes APU serial number, running time, cycle and other information. The operation parameters for starting the aircraft engine consist of sections N1 to S3; wherein, N1 and S1 represent the operation condition when the first aircraft engine is started, N2 and S2 represent the operation condition when the second aircraft engine is started, and N3 and S3 represent the condition when the APU is slowed down after the APU finishes starting the engine. And the starting parameters of the APU include: the starting time, the peak value of the EGT rotating speed, the lubricating oil temperature and the inlet temperature of the load compressor when the APU is started.

As can be seen from fig. 3, the APU operating parameter, i.e., the peak EGT rotation speed, is included in the existing message No. a 13. Therefore, the APU turbine efficiency detection of the invention can be realized by using the data acquired by the message.

FIG. 4 is a flow diagram of a method of monitoring APU turbine efficiency, in accordance with one embodiment of the present invention. As shown, in the APU turbine efficiency detection method 400, at step 410, the start state data at the start of the aircraft APU is obtained by obtaining the state data at the start of the aircraft APU for a period of time, wherein the start state data at least comprises the peak EGT speed.

According to one embodiment of the invention, the information required in step 410 may be obtained from an APU message, such as the A13 message. For example, an a13 message of the operation of the aircraft APU can be remotely acquired in real time from an international aviation telecommunication group SITA network control center and an ADCC network control center of national aviation data communication company, and the message decoder decodes the a13 message of the operation state of the aircraft APU to obtain the required start state information of the aircraft APU.

In step 420, an average value of the NPA is calculated for the time period based on the obtained peak EGT speed and the APU constant speed.

At step 430, it is determined whether the average value of the NPAs during the time period is close to a first threshold value. If the average value of the NPA has approached the first threshold value, then at step 440, it is determined that the turbine efficiency of the APU has entered a decline period.

At step 450, it is determined whether the average value of the NPAs over the period of time is close to a second threshold value. If the average value of the NPA has approached the second threshold value, then at step 460, it is determined that the turbine efficiency of the APU has entered a failure period.

According to one embodiment of the invention, the first threshold value is about 35% for an APU of APS3200 type; the second threshold is approximately 32%, and "close" means within approximately 1.5% of the gap. Similarly, for a GTCP131-9 type A APU, the first threshold is approximately 45%; the second threshold is approximately 40%, and "close" means within approximately 2.5% of the gap.

With this fixed time period, the average value of NPA gradually becomes better as time goes by. This method of analyzing a trend of change with data that is continuously updated over a period of time may be referred to as a moving window method. The size of the moving window, i.e. the number of points M that are included in the calculation range, is chosen depending on various factors, such as the interval of the measurement time, and the control strategy, etc. If the moving window is smaller, the fluctuation rate of the data is more easily influenced by normal fluctuation, so that excessive false alarm occurs, and the effect of the invention is influenced. If the moving window is too large, although the change trend is reflected more accurately, the timeliness of the invention is reduced, and the warning information cannot be sent out accurately in time. Therefore, the size of the moving window has an important influence on the present invention. According to one embodiment of the present invention, M is approximately 20 on the premise that 2-3 points are measured per day. According to another embodiment of the invention, M is about 10 on the premise that the measurement is less than or equal to 2 points per day.

According to one embodiment of the invention, there may be differences in the speed data obtained at different temperatures. In order to better reflect the turbine efficiency of the APU, the temperature influence is converted according to the rotation speed similarity characteristic, and NPAs can be converted into a uniform environment for comparison. The correction formula is as follows:

where Ncor is the NPA after correction, N is the NPA before correction, T0 is the reduced temperature, and T1 is the current temperature. Thus, the result after comparison with the threshold value is more accurate.

FIG. 5 is a flow diagram of a method of monitoring APU turbine efficiency, in accordance with another embodiment of the present invention. As shown, in the APU turbine efficiency detection method 500, at step 510, the start state data at the start of the aircraft APU is obtained by obtaining the state data at the start of the aircraft APU for a period of time, wherein the start state data at least comprises the peak EGT speed. According to one embodiment of the invention, the period of time is about 1-2 months.

According to one embodiment of the invention, the information required in step 510 may be obtained from an APU message, such as the A13 message. For example, an a13 message of the operation of the aircraft APU can be remotely acquired in real time from an international aviation telecommunication group SITA network control center and an ADCC network control center of national aviation data communication company, and the message decoder decodes the a13 message of the operation state of the aircraft APU to obtain the required start state information of the aircraft APU.

At step 520, based on the obtained peak EGT rpm and the APU constant rpm, the overall NPA for the time period is calculated.

At step 530, a linear or non-linear fit is made to all NPAs over the period of time, and the results of the fit are extrapolated linearly.

At step 540, it is determined that the turbine efficiency of the APU has entered the decay period if the intersection of the linear extrapolation result with the first threshold value is within about 1 month.

At step 550, it is determined that the turbine efficiency of the APU has entered a failure period if the intersection of the linear extrapolation result with the second threshold value is within about 1 month.

According to one embodiment of the invention, the first threshold value is about 35% for an APU of APS3200 type; the second threshold is approximately 32%, and "close" means within approximately 1.5% of the gap. Similarly, for a GTCP131-9 type A APU, the first threshold is approximately 45%; the second threshold is approximately 40%, and "close" means within approximately 2.5% of the gap.

In accordance with one embodiment of the invention, at steps 740 and 750, after the linear or non-linear fit, a confidence interval for the NPA is calculated. And estimating the time range of the efficiency of the APU entering the decline period or the fault period according to the intersection point of the extrapolation result of the confidence interval and the first threshold value and the second threshold value.

According to one embodiment of the invention, other APU startup parameters may also be used to help determine that the turbine efficiency of the APU enters the decline period. For example, peak EGTP of exhaust gas temperature at APU start. When the efficiency of the turbine is reduced, the peak EGTP of the exhaust gas temperature at the start of the APU will approach its red line value, i.e., the maximum exhaust gas temperature allowed for operation of the APU.

Since EGTP is also affected by the external temperature. According to one embodiment of the invention, the EGTP is modified. The correction formula is as follows:

EGTP_COR=((EGTP+273.5)/THITA)-273.5；

wherein EGTP _ COR is the corrected EGTP, and EGTP is the corrected EGTP, THITA = e ^ (- ((AltValue × CoverFt)/1000)/((8.51 × 273.15+ TATValue))/(9.8 × 29))), wherein AltValue is the altitude (meters), CoverFt is the (feet and meters conversion constant), and TATValue is the temperature (degrees celsius).

FIG. 6 is an example of APU turbine efficiency variation, according to one embodiment of the invention. Wherein the turbine efficiency of the APU is replaced in the position of the solid line in the figure. As shown in FIG. 6, prior to changing the APU turbine efficiency, the NPA gradually decreases to approach and exceed the first threshold value of 43% and gradually approaches the second threshold value of 40%. This is found if the method described above is used, so that an alarm is generated quickly that the APU turbine efficiency deteriorates, entering the decline period and the failure period. It should also be noted that the start time STA remains normal. The EGTA gradually enters the red line value of 840 degrees, and the corrected EGTA _ cor is also close to the red line value of 900 degrees.

FIG. 7 is a schematic structural diagram of an aircraft auxiliary power unit APU turbine efficiency monitoring apparatus in accordance with an embodiment of the present invention. As shown in fig. 7, the APU turbine efficiency monitoring device includes: a message acquiring unit 701, configured to acquire an APU message in a time period; a message parsing unit 702 that parses out the required operating data related to the turbine efficiency of the APU; and a turbine efficiency monitoring unit 703 that determines from the turbine efficiency operating data that the performance of the APU turbine efficiency is in a stable period, a decline period, or a failure period.

According to one embodiment of the invention, the performance detection device for the turbine efficiency of the auxiliary power unit APU of the airplane comprises the following components: a processor; and a memory coupled to the processor, storing computer readable code; the computer readable code running on the processor to perform the steps of: acquiring an APU message in a time period; analyzing the operation parameters related to the turbine efficiency of the APU according to the message, wherein the operation parameters comprise NPA; determining that the performance of the APU turbine efficiency is in a stable period, a decline period, a severe decline period or a failure period.

The above embodiments are provided only for illustrating the present invention and not for limiting the present invention, and those skilled in the art can make various changes and modifications without departing from the scope of the present invention, and therefore, all equivalent technical solutions should fall within the scope of the present invention.

Claims (12)

1. A method for detecting the turbine efficiency performance of an Auxiliary Power Unit (APU) of an aircraft comprises the following steps:

acquiring APU messages at a plurality of time points in a time period;

acquiring starting parameters of the APU according to the APU message, wherein the starting parameters at least comprise peak EGT rotating speed;

calculating the ratio NPA of the rotating speed at the exhaust temperature peak value when the APU is started relative to the rotating speed when the APU normally operates;

calculating an average of the NPAs over the time period; and

determining that the APU turbine efficiency is in a stable period, a decline period or a fault period according to the average value of the NPA,

wherein the step of determining that the APU turbine efficiency is in a stationary period, a decay period, or a fault period comprises:

in response to the mean value of the NPA in the time period approaching the second

A threshold value, determining that the APU turbine efficiency is in a decline period; and

determining that the APU turbine efficiency is in a failure period in response to the average of the NPAs over the time period approaching a second threshold value.

2. The method of claim 1 wherein the first threshold value is 35% for an APU type APS 3200; the second threshold is 32% and is close to within 1.5%.

3. The method of claim 1 wherein the first threshold value is 45% for GTCP131-9 type a APUs; the second threshold is 40% and is close to within 2.5%.

4. The method of claim 1 wherein 10-20 APU messages are acquired during the time period.

5. The method of claim 1, further comprising:

performing linear or nonlinear fitting on all NPAs in the period of time, and linearly extrapolating the fitted result;

determining that the turbine efficiency of the APU enters a decay period if the intersection of the linear extrapolation result and the first threshold value is within 1 month; and

and determining that the turbine efficiency of the APU enters a failure period if the intersection of the result of the linear extrapolation and the second threshold value is within 1 month.

6. The method of claim 5, further comprising: after linear or non-linear fitting, the confidence interval of the NPA is calculated.

7. The method of claim 6, further comprising: and estimating the time range of the efficiency of the APU entering the decline period or the failure period according to the intersection point of the extrapolation result of the confidence interval and the first threshold value and the second threshold value.

8. The method of claim 1, further comprising: it is determined whether the peak EGTP of the exhaust temperature at the start of the APU is near the red line value.

9. The method of claim 1, further comprising: and determining whether the corrected peak value EGTP of the exhaust temperature at the starting time of the APU is close to a red line value or not, wherein the correction formula is as follows:

EGTP_COR＝((EGTP+273.5)/THITA)-273.5；

wherein, EGTP _ COR is EGTP after correction, and EGTP is EGTP before correction, THITA ^ e (- (AltValue: CoverFt)/1000)/((8.51 ^ (273.15+ TATValue))/(9.8 ^ 29))),

where AltValue is altitude, CoverFt is the foot and meter transition constant, and TATValue is temperature.

10. The method of claim 1, further comprising: it is determined that the start time STA is within a normal range.

11. A performance detection apparatus for turbine efficiency of an aircraft auxiliary power unit, APU, comprising:

the message acquisition unit acquires an APU message in a time period;

the message analysis unit is used for analyzing required APU starting parameters, and the starting parameters at least comprise peak value EGT rotating speed; and

a performance detection unit for determining, based on the NPA, that the performance of the APU turbine efficiency is in a stationary phase, a decay phase or a fault phase,

the performance detection device also calculates the ratio NPA of the rotating speed at the exhaust temperature peak value when the APU is started relative to the rotating speed when the APU is in normal operation, calculates the average value of the NPA in the time period,

wherein the performance detection unit determines that the APU turbine efficiency is in a decline period in response to an average of the NPAs over the time period approaching a first threshold; determining that the APU turbine efficiency is in a failure period in response to the average of the NPAs over the time period approaching a second threshold value.

12. A performance detection apparatus for turbine efficiency of an aircraft auxiliary power unit, APU, comprising:

a processor; and

a memory coupled to the processor, storing computer readable code;

the computer readable code running on the processor to perform the steps of:

acquiring an APU message in a time period;

analyzing starting parameters of the APU according to the message, wherein the starting parameters at least comprise peak EGT rotating speed;

calculating the ratio NPA of the rotating speed at the exhaust temperature peak value when the APU is started relative to the rotating speed when the APU normally operates;

calculating an average of the NPAs over the time period; and

determining that the APU turbine efficiency is in a stable period, a decline period or a fault period according to the average value of the NPA,

wherein the step of determining that the APU turbine efficiency is in a stationary period, a decay period, or a fault period comprises:

determining that the APU turbine efficiency is in a decline period in response to the average of the NPAs over the time period approaching a first threshold value; and

determining that the APU turbine efficiency is in a failure period in response to the average of the NPAs over the time period approaching a second threshold value.