CN110887668A

CN110887668A - Method and system for detecting and accommodating loss of torque signal

Info

Publication number: CN110887668A
Application number: CN201811056175.9A
Authority: CN
Inventors: S.拉马瑞; F.卡萨万; J-P.罗耶
Original assignee: Pratt and Whitney Canada Corp
Current assignee: Pratt and Whitney Canada Corp
Priority date: 2018-09-11
Filing date: 2018-09-11
Publication date: 2020-03-17

Abstract

Systems and methods for detecting and accommodating for loss of torque signal of a gas turbine engine are described herein. An engine degradation offset may be determined when a torque signal of the engine is available. A predicted operating offset may then be determined in the event of a loss of torque signal. At least partially from the engine degradation offset and predicted operation offset, a resultant torque signal may be generated when a torque signal is lost.

Description

Method and system for detecting and accommodating loss of torque signal

Technical Field

The present disclosure relates generally to engine control and, more particularly, to detecting and accommodating loss of a torque signal.

Background

Turboshaft and turboprop engines for aircraft typically use torque signals to manage torque or power. In the unlikely event of loss of torque signal, it is desirable to design the engine control system such that engine control is maintained. The loss of torque signal may be temporary or permanent, and may be the result of a sensor failure, physical damage, or an interruption of the electrical signal. Furthermore, in some engine hardware configurations, the torque signal of the system may be sensitive to aircraft handling.

Accordingly, there is a need for improved systems and methods for detecting and accommodating loss of torque signals.

Disclosure of Invention

In one aspect, a method for accommodating loss of torque signal of a gas turbine engine is provided. The method comprises the following steps: determining an engine degradation offset when a torque signal of the engine is available; determining a predicted operating offset when the torque signal is lost; and generating a resultant torque signal when the torque signal is lost at least partially from the engine degradation offset and the predicted operating offset.

In another aspect, a system for accommodating loss of torque signal of a gas turbine engine is provided. The system comprises: at least one processing unit; and a non-volatile computer readable memory having stored thereon program instructions executable by the at least one processing unit. The program instructions are executable by the at least one processing unit to: determining an engine degradation offset when a torque signal of the engine is available; determining a predicted operating offset when the torque signal is lost; and generating a resultant torque signal when the torque signal is lost at least partially from the engine degradation offset and the predicted operating offset.

Drawings

Referring now to the drawings wherein:

FIG. 1 is a schematic cross-sectional view of an exemplary engine of an aircraft;

FIG. 2 is a flow chart illustrating an exemplary method for accommodating loss of a torque signal of an engine, according to an embodiment;

FIG. 3 is an exemplary graphical illustration of a baseline expectation curve;

FIG. 4 is an exemplary graphical illustration of an adjusted expected curve shifted from the baseline expected curve of FIG. 3 by an engine rotational speed offset;

FIG. 5 is an exemplary graphical illustration of an adjusted expected curve shifted from the baseline expected curve of FIG. 3 by an actual operating offset;

FIG. 6 is an exemplary graphical illustration showing an engine degradation offset determined from the engine rotational speed offset of FIG. 4 and the actual operating offset of FIG. 5;

FIG. 7 is an exemplary graphical illustration showing a predicted operating offset determined from the baseline expectation curve of FIG. 3;

FIG. 8 is an exemplary graphical illustration showing an adjusted expected curve determined from the predicted operating offset of FIG. 7 and the engine degradation offset of FIG. 6; and

fig. 9 is a schematic diagram of an exemplary computing system for implementing the method of fig. 2, according to an embodiment.

It will be noted that throughout the drawings, like features are indicated with like reference numerals.

Detailed Description

FIG. 1 illustrates a gas turbine engine 10, the loss of torque signal of which may be detected and accommodated using the systems and methods described herein. Engine 10 generally includes the following components in series flow communication: a propeller 120 attached to the shaft 108 through which ambient air is propelled; a compressor section 114 for pressurizing the air; a combustor 116 in which compressed air is mixed with fuel and ignited for generating an annular flow of hot combustion gases; and a turbine section 106 for extracting energy from the combustion gases.

Control system 50 is used to control the operation of engine 10. Control system 50 may be configured to receive one or more operating parameter signals related to the operation of engine 10. The operating parameter signals may be, for example, from one or more sensors (not shown) associated with engine 10. According to an embodiment, the operating parameter signal includes a torque of the engine 10. Control system 50 may be configured to send one or more control signals to engine 10 to control the operation of engine 10. According to an embodiment, the control signal includes a power setting to set engine 10 at a particular power under particular environmental and draw conditions. Control system 50 may implement one or more power setting functions to perform various calculations and/or operations associated with engine 10. Although control system 50 is described as being external to the engine, this is for descriptive purposes only and control system 50 may be internal or external to engine 10. In a specific and non-limiting example of embodiment, the control system 50 may be implemented in an internal gas-generator control circuit of the engine 10. In another specific and non-limiting example of an embodiment, the control system 50 may be implemented in an Electronic Engine Controller (EEC) as part of a full authority digital engine (or electronic) control (FADEC).

Referring to FIG. 2, a flowchart depicting an exemplary method 200 for accommodating loss of the torque signal of engine 10 is shown. The method 200 may be implemented by a control system 50 associated with the engine 10.

In step 202, the control system 50 determines an engine degradation offset (deltaNG — det) when a torque signal for the engine 10 is available. When deltaNG _ det mainly includes engine degradation, deltaNG _ det corresponds to the sum of, as a whole: degradation of the engine; engine manufacturing variability; aligning the engine model; installation impact (e.g., external expectations, etc.); variability (e.g., variability between aircraft, manufacturing variability, installation variability, etc.); and deterioration or damage (e.g., dirt, impurity damage, etc.) of the mounting efficiency. There may be an offset in the fuel flow applied by the control system 50 to meet the power requirements of a particular operating condition. deltaNG _ det may be determined by taking the difference between the engine rotational speed offset (deltaNG (pi)) and the actual operating offset (deltaNG _ rat) when the torque signal for the engine is available. For example, the deltaNG _ det may be determined using the following equation:

deltaNG _ det = deltaNG (PI) -deltaNG _ rat (Eq. 1)

Referring also to fig. 3, an example of a baseline non-normalized expected curve 302 is shown, where the x-axis corresponds to engine rotational speed (NG) and the y-axis corresponds to engine power (SHP). Thus, baseline non-normalized expected curve 302 defines a relationship between SHP and NG of engine 10 at particular environmental conditions. An expected profile of the type shown in FIG. 3 may be used as a baseline to manage control of engine 10 based on the resulting torque in the event of a torque failure.

While the baseline expected curve 302 may be modeled to theoretically correspond to the engine 10, due to various factors such as the operating conditions of the engine 10 and/or the selected operation of the aircraft, it should be appreciated that the engine 10 delivery power schedule may not directly correspond to the expected curve 302 during operation.

Referring also to fig. 4, an example of a first adjusted expected curve 301 is shown shifted from a baseline expected curve 302 to deltang (pi) 300. As further shown, reference 305 shows the reference rotational speed, reference 303 shows the actual NG, and reference 304 shows the actual transmitted power of the engine 10. The reference rotational speed 305 corresponds to an expected rotational speed of the engine 10 for the actual transmitted power 304 of the engine 10. During steady state operation of the engine 10, an error may occur between the reference (or predicted) rotational speed 305 and the actual NG 303 required by the engine 10. Thus, the error between the expected curve 302 and the actual NG 303 at the reference rotational speed 305 may be calculated to determine the deltang (pi) 300. Specifically, the deltang (pi)300 may be determined from a difference between a reference rotational speed 305 of the engine 10 from the baseline expected curve 302 for the actual delivered power 304 of the engine 10 and an actual NG 303 of the engine 10 for the actual delivered power 304 of the engine 10. More specifically, when the torque signal is active and the engine 10 is managed in steady state operation, the torque signal may be used to determine the actual power delivered 304 by the engine 10. The actual NG 303 may then be compared to a reference NG305 from the baseline expected curve 302 to determine a deltang (pi)300 at the actual engine power 304.

The DeltaNG (PI)300 may be determined at regular or irregular intervals, as it may change over time. The interval used to determine DeltaNG (PI)300 may be set to any suitable interval (e.g., daily, hourly, per minute, etc.) when engine 10 is in steady state operation. Generally, steady state operation of engine 10 refers to: all parameters of engine 10, such as fuel flow, engine temperature, engine rotational speed, torque, etc., are stable; there is no pilot input that changes the condition of the engine 10; constant draw, such as bleed air, load, etc.; and constant environmental conditions such as altitude and air temperature, etc.

Referring to fig. 5, an example of a second adjusted expected curve 307 is shown drifting from the baseline expected curve 302 to the actual deltaNG _ rate 308. Numeral 316 is shown to describe the maximum rated power of engine 10 from ambient conditions and draw. According to an embodiment, the power setting function of the control system 50 is used to derive the actual deltaNG _ rat 308. For example, the power setting function of control system 50 may determine a maximum rated power 316 and a corresponding NG for engine 10. The maximum rated power 316 and corresponding NG of the engine 10 may be determined at a particular time, such as at takeoff or another operating condition where the engine 10 is at a maximum continuous rating. The actual deltaNG _ rat 308 may then be determined from the difference between the NG at the maximum rated power 316 and the corresponding NG at the same power from the baseline expected curve 302. The determination of the actual deltaNG _ rat 308 may be done in real time and may not require that the torque signal be active.

According to an embodiment, the actual deltaNG _ rat 308 may be determined from the NG difference between the baseline expected curve 302 and the second adjusted expected curve 307 set at the maximum rated power 316 of the engine 10. That is, based on the maximum rated power 316 of engine 10, baseline expected curve 302 may be shifted to obtain second adjusted expected curve 307. In this example, the NG difference between the baseline expected curve 302 and the second adjusted expected curve 307 is the actual deltaNG _ rat 308. It is noted that the second expected curve 307 need not be determined and is shown herein for descriptive purposes.

According to an embodiment, the drift of the baseline expected curve 302 used to derive the second adjusted expected curve 307 may be completed at a particular time, such as at takeoff or another operating condition where the engine 10 is at a maximum continuous rating. The drifting of the baseline expected curve 302 used to determine the second adjusted expected curve 307 may be accomplished such that the second adjusted expected curve 307 is aligned with the operating conditions and the aircraft selection operation.

The actual deltaNG _ rat 308 may be calculated at the maximum rated power 316 of the engine 10 because test data and engine models have shown that the difference in NG may be approximated as

Is constant over the operating range of engine 10.

Referring to FIG. 6, an example shows how the deltaNG _ det 310 can be determined from the deltaNG (PI)300 and the actual deltaNG _ rat 308 when a torque signal is available. As shown, deltaNG _ det 310 is determined from the difference between deltaNG (pi)300 and deltaNG _ rat 308 (i.e., deltaNG _ det = deltaNG (pi) -deltaNG _ rat) when the torque signal for the engine is available.

Referring back to FIG. 2, in step 208, in the event of a loss of torque signal, the control system 50 determines a predicted deltaNG _ rat. Referring now to FIG. 7, an example of a non-normalized baseline expectation curve 302 and a marker 318 are shown, the marker 318 showing the predicted NG for the engine 10 for a particular stable power rating of the engine 10. When the torque signal is lost, the predicted deltaNG _ rat 350 may be determined from the difference between the baseline expected curve 302 and the predicted NG318 for a particular stable power rating determined by the power setting function of the control system 50. For example, the power setting function may be able to determine the predicted NG318 required for a particular operating condition. That is, the control system 50 may be able to predict the NG required for a particular power demand that matches the particular operating condition.

The control system 50 may be capable of predicting NG for an operating condition, such as bleed air, load, entry gate, climb, takeoff, landing, maximum power, continuous power, and/or any other suitable operating condition. The engine operating conditions may be a function of one or more of ambient conditions and aircraft draw. The environmental conditions may include outside air temperature, latitude, aircraft speed, and the like. Aircraft draw and configuration may include induced draw, AGB load draw, inlet bypass configuration (e.g., bypass doors), and the like. Thus, determining the predicted deltaNG _ rat 350 when the torque signal is lost may include: this is done for specific operating conditions related to environmental conditions and/or aircraft draw and/or configuration.

The actual deltaNg _ rat and predicted deltaNg _ rat will typically be the same if neither the operating conditions, environmental conditions, and/or aircraft draw have changed before or after the loss of the torque signal.

According to an embodiment, when the torque signal is lost, a respective stable power rating is calculated for each of a plurality of engine operating conditions. Then, for each engine operating condition, a corresponding predicted NG can be determined. Each respective predicted NG can be determined by predicting the NG required for the respective stable power rating corresponding to the respective operating condition. This may be accomplished by controlling the power setting function of the system 50. Thus, a respective predicted deltaNG _ rat may then be calculated for each engine operating condition after the torque signal is lost. Each of these respective predicted deltaNG _ rates may be calculated from the difference between the baseline expected curve 302 and the respective predicted NG at the corresponding respective rated power of the engine 10 for that operating condition.

In step 210, the control system 50 generates a resultant torque signal when the torque signal is lost, at least in part from the deltaNG _ det 310 and the predicted deltaNG _ rat 350. When the torque signal is lost, the control system 50 is no longer able to determine deltaNG (PI) based on the torque signal. Thus, by rearranging equation (1), the following equation can be determined:

deltaNG (PI) = deltaNG _ rat + deltaNG _ det (Eq. 2)

The DeltaNG _ det 310 has been previously determined at step 202 and may be used after the torque signal is lost. The predicted deltaNG _ rat when the torque signal is lost has been determined in step 208. Thus, at step 210, a predicted deltaNG (PI) may be determined from equation (2), and a resultant torque signal may be determined from the predicted deltaNG (PI).

In some embodiments, generating the composite torque signal of step 210 comprises: deltaNG _ det 310 and predicted deltaNG _ rat 350 are applied to obtain the adjusted expected curve. Referring also to FIG. 8, a third adjusted expected curve 324 is shown. In this example, the third adjusted expected curve 324 is determined by shifting the baseline expected curve 302 by the predicted deltaNG _ rat 350 of FIG. 7 and the deltaNG _ det 310 of FIG. 6. More specifically, the deltaNG _ det 310 determined when the torque signal is available (e.g., step 202) and the predicted deltaNG _ rat 350 determined when the torque signal is missing (e.g., step 208) may be added to the baseline expected curve 302 to obtain the third adjusted expected curve 324. That is, an offset 322 for adjusting the baseline expectation curve 302 may be determined. The offset 322 may be determined by adding the deltaNG _ det 310 and the predicted deltaNG _ rat 350. It should be appreciated that the offset 322 corresponds to the predicted deltaNG (PI) of equation (2).

Thus, generating the composite torque signal may include: applying deltaNG _ det 310 and predicted deltaNG _ rate 350 to baseline expected curve 302 to obtain third adjusted expected curve 324; and using the third adjusted expected curve 324 to derive a resultant torque signal.

According to some embodiments, deltaNG _ det 310 is added to each of the respective predicted deltaNG _ rates calculated for each stable operating condition following a loss of torque signal. Then, adding deltaNG _ det 310 and each respective predicted deltaNG _ rate for each respective stable condition after the failure to the baseline expected curve 302 defines a respective adjusted expected curve. Then, depending on the operating condition in which the aircraft is located, the corresponding adjusted expected curve for that operating condition may be used.

A specific and non-limiting example of how the predicted deltaNG _ rat 350 may be determined is now described. In this example, the baseline expected curve 302 indicates that the engine rotational speed should be 30,000 RPM, and the power setting indicates that the rotational speed is 31,000 RPM; the predicted deltaNG _ rat 350 would therefore be determined to be 31,000 RPM-30,000 RPM = 1,000 RPM. For example, if the deltaNG _ det 310 is determined to be 500 RPM with the torque signal available, the baseline expected curve 302 may drift by 1,000RPM + 500 RPM = 1,500 RPM to yield the third adjusted expected curve 324.

When the torque signal is available, the DeltaNG _ det 310 determined at step 202 may be periodically determined and stored during steady engine operation. According to an embodiment, the method 200 includes step 204, which includes storing the deltaNG _ det 310 when a torque signal for the engine is available. According to a specific and non-limiting example of an embodiment, deltaNG _ det 310 may be the only value that needs to be stored in the event of a failure of the torque signal (i.e., neither deltaNG (pi)300 nor the actual deltaNG _ rat 308 is stored).

The change in the engine rotational speed (deltaNG) caused by deterioration of the engine 10 may slowly change over the life of the engine 10 unless the engine 10 is damaged. Therefore, for simplicity, the deltaNG _ det 310 may be considered to be relatively constant throughout the engine rotational speed range. In some embodiments, however, the deltaNG det 310 may be phased out as the rotational speed is reduced to improve accuracy. This is because the deltaNG _ det 310 is generally less affected by operating conditions (e.g., bleed air draw, AGB load draw, inlet bypass configuration, bypass doors, outside air temperature, altitude, aircraft speed, etc.).

According to some embodiments, the method 200 includes a step 206, which includes: whether the torque signal is reliable is detected by comparing the measured torque value conveyed by the torque signal with deltang (pi)300 and an allowable tolerance.

The power (SHP) of engine 10 may be determined by: the Power Lever Angle (PLA) of the engine 10 is measured and the measured PLA is converted to SHP, which is then converted to an NG target value using the third adjusted expected curve 324. This may be accomplished by controlling the power setting function of the system 50. There may be various ways of determining the power of engine 10, such as using sensors to directly measure the power or calculating the power based on other engine parameters.

In the event that the torque signal is lost and the method 200 is applied, the cabin torque error may show the torque defined by the third adjusted expected curve 324 based on the current NG value. Other forms of warning or notification signals may of course be provided.

Although the expected curve is non-normalized in the examples described in connection with fig. 3 to 8, the expected curve may be non-normalized or normalized. Normalization refers to the expected curve being adjusted for temperature, pressure and/or altitude conditions. Thus, depending on the actual implementation, the baseline expectation curve may be a non-normalized baseline expectation or a normalized baseline expectation. Thus, there may be multiple baseline expectation curves for different temperatures and/or temperature ranges. Further, while examples are shown for calculating deltaNG _ det, deltaNG (PI), and deltaNG _ rat in relation to changes in engine rotational speed, in other embodiments using a normalized expectation curve, such calculations may be related to a normalized engine rotational speed (NgN). Thus, in some embodiments, engine 10 may be modeled based on a relationship between normalized engine rotational speed (NgN) and normalized engine power.

It should be appreciated that in the embodiment described herein, the difference between third adjusted expected curve 324 and baseline expected curve 302 is constant throughout the operating range of engine 10. For certain embodiments, to improve low power accuracy, the deltaNG _ det and deltaNG _ rat may be scaled down by normalizing the engine rotational speed such that the delivered power of the engine 10 at low power approximately coincides with the baseline expected curve 302. According to another embodiment, generating the composite torque signal comprises: deltaNG _ det and deltaNG _ rat are scaled down by normalizing the engine rotational speed to produce a resultant torque signal.

The method 200 may be applied to accommodate permanent loss of torque signals and/or temporary loss of torque signals. For example, a temporary loss of torque signal may occur during times when aircraft and/or engine conditions change, and the method 200 may accommodate such temporary loss of torque signal.

Referring to fig. 9, the method 200 may be implemented by a computing device 910 that includes a processing unit 912 and a memory 914, having stored therein computer-executable instructions 916. The processing unit 912 may include any suitable device configured to implement the system such that, when executed by the computing device 910 or other programmable apparatus, the instructions 916 may result in performance of the functions/acts/steps of the method 200 as described herein. Processing unit 912 may include, for example, any type of general purpose microprocessor or microcontroller, a Digital Signal Processing (DSP) processor, a Central Processing Unit (CPU), an integrated circuit, a Field Programmable Gate Array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuitry, or any combination thereof.

Memory 914 may include any suitable known or other machine-readable storage medium. The memory 914 may include a non-transitory computer readable storage medium such as, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory 914 may comprise any type of suitable combination of computer memory located internal or external to the device, such as Random Access Memory (RAM), Read Only Memory (ROM), Compact Disc Read Only Memory (CDROM), electro-optic memory, magneto-optic memory, Erasable Programmable Read Only Memory (EPROM) and Electrically Erasable Programmable Read Only Memory (EEPROM), ferroelectric RAM (fram), and the like. Memory 914 may include any storage mechanism (e.g., device) suitable for retrievably storing machine-readable instructions 916 executable by processing unit 912.

The methods and systems for detection and adaptation described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or facilitate the operation of a computing system (e.g., computing device 910). Alternatively, the method and system for detection and adaptation may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems for detection and adaptation may be stored on a storage medium or device, such as a ROM, magnetic disk, optical disk, flash drive, or any other suitable storage medium or device. The program code can be read by a general-purpose or special-purpose programmable computer, to construct and operate the computer when the storage medium or device is read by the computer to execute the procedures described herein. Embodiments of the method and system for detection and adaptation may also be considered to be implemented by means of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may include computer readable instructions that cause a computer (or in some embodiments, the processing unit 912 of the computing device 910) to operate in a specific and predefined manner to perform the functions described herein.

Computer-executable instructions may take many forms, including program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

The control system may include power setting logic for implementing the power setting function, and the power setting logic may require modification (e.g., additional memory requirements) to suit the embodiments described herein.

The terms "first," "second," and "third" used in connection with "adjusted intended" are used to identify different intended curves in this document and the drawings for purposes of example and are not intended to be limiting.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Other variations that fall within the scope of the invention will be apparent to those skilled in the art upon reading this disclosure.

Various aspects of the method and system for controlling operation of a first propeller of an aircraft may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. While particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples, but should be accorded the broadest reasonable interpretation consistent with the description as a whole.

Claims

1. A method for accommodating loss of torque signal of a gas turbine engine, the method comprising:

determining an engine degradation offset when a torque signal of the engine is available;

determining a predicted operating offset when the torque signal is lost; and

generating a resultant torque signal when a torque signal is lost at least partially from the engine degradation offset and a predicted operating offset.

2. The method of claim 1, wherein generating the composite torque signal comprises: applying the engine degradation offset and predicted operating offset to a baseline expected profile of the engine defining a relationship between engine power and engine rotational speed to obtain an adjusted expected profile.

3. The method of claim 2, wherein determining the engine degradation offset comprises: a difference between an engine rotational speed offset and an actual operating offset when a torque signal for the engine is available is determined.

4. The method of claim 3, wherein determining the engine degradation offset comprises: determining the engine rotational speed offset from a difference between a reference rotational speed of the engine from a baseline expected profile for an actual delivered power of the engine and an actual rotational speed of the engine.

5. The method of claim 3, wherein determining the engine degradation offset comprises: determining an actual operating offset when a torque signal for the engine is available from a rotational speed difference between a baseline expected profile set at a maximum rated power of the engine and an adjusted expected profile.

6. The method of claim 1, further comprising: storing the engine degradation offset when a torque signal of the engine is available.

7. The method of claim 1, further comprising: detecting whether the torque signal is reliable, and wherein the resultant torque signal is generated when the torque signal is found to be unreliable.

8. The method of claim 2, wherein determining a predicted operating offset when a torque signal is lost comprises: the predicted operating offset is determined from a difference between the baseline expected profile and an engine rotational speed determined from a power setting of the engine at an actual rated power of the engine.

9. The method of claim 8, wherein determining a predicted operating offset when a torque signal is lost comprises: a predicted operating offset is determined for a particular operating condition associated with an environmental condition and an aircraft draw.

10. The method of claim 2, wherein generating the composite torque signal comprises: scaling the engine degradation offset and the predicted operating offset by normalizing an engine rotational speed to generate the resultant torque signal.

11. A system for accommodating loss of torque signal of a gas turbine engine, the system comprising:

at least one processing unit; and

a non-transitory computer readable memory having stored thereon program instructions executable by the at least one processing unit to:

determining a predicted operating offset when the torque signal is lost; and

12. The system of claim 11, wherein generating the composite torque signal comprises: applying the engine degradation offset and predicted operating offset to a baseline expected profile of the engine defining a relationship between engine power and engine rotational speed to obtain an adjusted expected profile.

13. The system of claim 12, wherein determining the engine degradation offset comprises: a difference between an engine rotational speed offset and an actual operating offset when a torque signal for the engine is available is determined.

14. The system of claim 13, wherein determining the engine degradation offset comprises: determining the engine rotational speed offset from a difference between a reference rotational speed of the engine from a baseline expected profile for an actual delivered power of the engine and an actual rotational speed of the engine.

15. The system of claim 14, wherein determining the engine degradation offset comprises: determining an actual operating offset when a torque signal for the engine is available from a rotational speed difference between a baseline expected profile set at a maximum rated power of the engine and an adjusted expected profile.

16. The system of claim 10, wherein the program instructions are further executable by the processing unit for storing the engine degradation offset when a torque signal of the engine is available in the non-volatile computer readable memory.

17. The system of claim 10, wherein the program instructions are further executable by the processing unit for detecting whether the torque signal is reliable, and wherein the resultant torque signal is generated when the torque signal is found to be unreliable.

18. The system of claim 12, wherein determining the predicted operating offset when the torque signal is lost comprises: the predicted operating offset is determined from a difference between the baseline expected profile and an engine rotational speed determined from a power setting of the engine at an actual rated power of the engine.

19. The system of claim 18, wherein determining a predicted operating offset when a torque signal is lost comprises: a predicted operating offset is determined for a particular operating condition associated with an environmental condition and an aircraft draw.

20. The system of claim 12, wherein generating the composite torque signal comprises: scaling the engine degradation offset and the predicted operating offset by normalizing an engine rotational speed to generate the resultant torque signal.