Patent Publication Number: US-2021172836-A1

Title: Methods and apparatus for inspecting an engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This specification is based upon and claims the benefit of priority from UK Patent Application Number 1918094.2 filed on 10 th  December 2019, the entire contents of which are incorporated herein by reference. 
     TECHNOLOGICAL FIELD 
     The present disclosure concerns methods and apparatus for inspecting an engine. 
     BACKGROUND 
     Aircraft typically comprise one or more engines for providing propulsive thrust and/or electrical energy to the aircraft. During operation, the one or more engines may become damaged (for example, due to relatively high operating temperatures or due to foreign object damage). Aircraft engines are usually inspected at regular intervals by a human inspector to determine the condition of components within the engine. Where components are found to be in an unacceptable condition, the engine is usually removed from the aircraft for repair. During such inspections, the aircraft is grounded and is not available for operation by the airline. Additionally, the quality and duration of the inspection is dependent upon the skill and experience of the inspector. 
     BRIEF SUMMARY 
     According to a first aspect there is provided a method comprising: inspecting an engine during a first period of time to identify damage, the engine being associated with an aircraft; receiving three-dimensional data of one or more components of the engine, the three-dimensional data being generated during the first period of time; determining, during the first period of time, whether the identified damage exceeds a threshold; providing instructions to release the aircraft for operation in a second period of time, subsequent to the first period of time, if the identified damage does not exceed the threshold; and inspecting the received three-dimensional data during the second period of time to measure damage. 
     Inspecting the received three-dimensional data may comprise: identifying a feature of the component using the three-dimensional data; determining coordinates of the feature in the three-dimensional data; and measuring a parameter of the feature of the component using the determined coordinates of the feature in the three-dimensional data. 
     The method may further comprise: receiving data comprising two-dimensional data of the component of the engine, the two-dimensional data being generated during the first period of time; and wherein inspecting the received three-dimensional data comprises: identifying a feature of the component using the two-dimensional data; determining coordinates of the feature in the two-dimensional data; determining coordinates of the feature in the three-dimensional data using: the determined coordinates of the feature in the two-dimensional data; and a pre-determined transformation between coordinates in two-dimensional data and coordinates in three-dimensional data; and measuring a parameter of the feature of the component using the determined coordinates of the feature in the three-dimensional data. 
     Prior to identifying the feature of the component using the two-dimensional data, the method may further comprise: identifying the feature of the component using the three-dimensional data; determining coordinates in the three-dimensional data of a first volume bounding the coordinates of the feature; determining coordinates of a first area in the two-dimensional data corresponding to the first volume using: the determined coordinates of the first volume in the three-dimensional data; and the predetermined transformation. 
     Identifying the feature of the component using the two-dimensional data may comprise using a subset of the two-dimensional data corresponding to the first area. 
     Determining coordinates in the three-dimensional data of the first volume may comprise: identifying the first volume in the three-dimensional data using: the identified feature of the component; and a three-dimensional model of the component. 
     Prior to identifying the feature of the component using the three-dimensional data, the method may further comprise: identifying a second area using the two-dimensional data of the component, the second area excluding predetermined components and/or predetermined sub-components of the engine within the two-dimensional data; determining coordinates of a second volume in the three-dimensional data corresponding to the second area using: the determined coordinates of the second area in the two-dimensional data; and the predetermined transformation. 
     Identifying the feature of the component using the three-dimensional data may comprise: identifying the feature of the component using a subset of the three-dimensional data corresponding to the second volume. 
     The method may further comprise: controlling storage of the measured parameter. 
     Inspecting the received three-dimensional data during the second period of time may be performed by a computer. 
     Inspecting the received three-dimensional data during the second period of time may be performed automatically by the computer in response to receiving the three-dimensional data. 
     Inspecting the received three-dimensional data may be performed during a predetermined period of time from release of the aircraft for operation. 
     According to a second aspect there is provided a computer program that, when executed by a computer, causes the computer to perform the method as described in the preceding paragraphs. 
     According to a third aspect there is provided a non-transitory computer readable storage medium comprising computer readable instructions that, when executed by a computer, causes the computer to perform the method as described in any of the preceding paragraphs. 
     According to a fourth aspect there is provided an apparatus comprising: a controller configured to perform the method as described in any of the preceding paragraphs. 
     According to a fifth aspect there is provided a computer-implemented method comprising: receiving data comprising two-dimensional data and three-dimensional data of a component of an engine; identifying a feature of the component using the two-dimensional data; determining coordinates of the feature in the two-dimensional data; determining coordinates of the feature in the three-dimensional data using: the determined coordinates of the feature in the two-dimensional data; and a pre-determined transformation between coordinates in two-dimensional data and coordinates in three-dimensional data; and measuring a parameter of the feature of the component using the determined coordinates of the feature in the three-dimensional data. 
     Prior to identifying the feature of the component, the method may further comprise: identifying the feature of the component using the three-dimensional data; determining coordinates in the three-dimensional data of a first volume bounding the coordinates of the feature; determining coordinates of a first area in the two-dimensional data corresponding to the first volume using: the determined coordinates of the first volume in the three-dimensional data; and the predetermined transformation. 
     Identifying the feature of the component using the two-dimensional data may comprise using a subset of the two-dimensional data corresponding to the first area. 
     Determining coordinates in the three-dimensional data of the first volume may comprises: identifying the first volume in the three-dimensional data using: the identified feature of the component; and a three-dimensional model of the component. 
     Prior to identifying the feature of the component using the three-dimensional data, the method may further comprise: identifying a second area using the two-dimensional data of the component, the second area excluding predetermined components and/or predetermined sub-components of the engine within the two-dimensional data; determining coordinates of a second volume in the three-dimensional data corresponding to the second area using: the determined coordinates of the second area in the two-dimensional data; and the predetermined transformation. 
     Identifying the feature of the component using the three-dimensional data comprises: identifying the feature of the component using a subset of the three-dimensional data corresponding to the second volume. 
     The method may further comprise: controlling storage of the measured parameter. 
     The engine may be associated with an aircraft, and the data may be generated during a first period of time in which the aircraft is not released for operation. 
     The computer-implemented method may be performed during a second period of time in which the aircraft is released for operation. 
     The computer-implemented method may be performed automatically in response to receiving the data. 
     The computer-implemented method may be performed without human intervention. 
     According to a sixth aspect there is provided a computer program that, when executed by a computer, causes the computer to perform the computer-implemented method as described in any of the preceding paragraphs. 
     According to a seventh aspect there is provided a non-transitory computer readable storage medium comprising computer readable instructions that, when executed by a computer, causes the computer to perform the computer-implemented method as described in any of the preceding paragraphs. 
     According to an eighth aspect there is provided an apparatus comprising: a controller configured to perform the computer-implemented method as described in any of the preceding paragraphs. 
     According to a ninth aspect there is provided a method comprising: inspecting an industrial system during a first period of time to identify damage; receiving three-dimensional data of one or more components of the industrial system, the three-dimensional data being generated during the first period of time; determining, during the first period of time, whether the identified damage exceeds a threshold; providing instructions to enable operation of the industrial system in a second period of time, subsequent to the first period of time, if the identified damage does not exceed the threshold; and inspecting the received three-dimensional data during the second period of time to measure damage. 
     According to a tenth aspect there is provided a method comprising: inspecting an engine during a first period of time to identify damage, the engine being associated with an aircraft; receiving two-dimensional data of one or more components of the engine, the two-dimensional data being generated during the first period of time; determining, during the first period of time, whether the identified damage exceeds a threshold; providing instructions to release the aircraft for operation in a second period of time, subsequent to the first period of time, if the identified damage does not exceed the threshold; and inspecting the received two-dimensional data during the second period of time to measure damage. 
     According to an eleventh aspect there is provided a method comprising: inspecting an industrial system (for example, an engine) during a first period of time to identify damage (the engine may, or may not be associated with an aircraft); receiving data of one or more components of the industrial system, the data being generated during the first period of time; determining, during the first period of time, whether the identified damage exceeds a threshold; providing instructions to enable operation of the industrial system in a second period of time, subsequent to the first period of time, if the identified damage does not exceed the threshold; and inspecting the received data during the second period of time to measure damage. 
     The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein. 
    
    
     
       BRIEF DESCRIPTION 
       Embodiments will now be described by way of example only, with reference to the Figures, in which: 
         FIG. 1  illustrates a schematic diagram of an apparatus for inspection of an engine according to various examples; 
         FIG. 2  illustrates a cross sectional side view of a gas turbine engine according to various examples; 
         FIG. 3  illustrates a close-up sectional side view of an upstream portion of the gas turbine engine illustrated in  FIG. 2 ; 
         FIG. 4  illustrates a partially cut-away view of the gearbox of the gas turbine engine illustrated in  FIGS. 2 and 3 ; 
         FIG. 5  illustrates a flow diagram of a first method of inspecting an engine; 
         FIG. 6  illustrates a time line diagram of the first method of inspecting an engine; 
         FIG. 7  illustrates a time line diagram of a second method of inspecting an engine; 
         FIG. 8  illustrates a flow diagram of a third method of inspecting an engine; 
         FIG. 9  illustrates a side view of a turbine blade according to a first example; 
         FIG. 10  illustrates a side view of a turbine blade according to a second example; 
         FIG. 11  illustrates a side view of a turbine blade according to a third example; 
         FIG. 12  illustrates a flow diagram of a fourth method of inspecting an engine; 
         FIG. 13  illustrates a flow diagram of a fifth method of inspecting an engine; and 
         FIG. 14  illustrates a flow diagram of a sixth method of inspecting an engine. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, the terms ‘connected’ and ‘coupled’ mean operationally connected and coupled. It should be appreciated that there may be any number of intervening components between the mentioned features, including no intervening components. 
       FIG. 1  illustrates a schematic diagram of an apparatus  10  for inspecting an engine  12  according to various examples. The apparatus  10  includes: a controller  14 ; a user input device  16 ; a display  18 ; and an inspection device  20  comprising a sensor  22 . 
     In some examples, the apparatus  10  may be a module. As used herein, the wording ‘module’ refers to a device or apparatus where one or more features are included at a later time and, possibly, by another manufacturer or by an end user. For example, where the apparatus  10  is a module, the apparatus  10  may only include the controller  14 , and the remaining features (such as the user input device  16 , the display  18 , the inspection device  20  and the sensor  22 ) may be added by another manufacturer, or by an end user. 
     The controller  14 , the user input device  16 , the display  18 , the inspection device  20  and the sensor  22  may be coupled to one another via a wireless link and may consequently comprise transceiver circuitry and one or more antennas. Additionally, or alternatively, the controller  14 , the user input device  16 , the display  18 , the inspection device  20  and the sensor  22  may be coupled to one another via a wired link and may consequently comprise interface circuitry (such as a Universal Serial Bus (USB) plugs and sockets). 
     The controller  14  may comprise any suitable circuitry to cause performance of the methods described herein and as illustrated in  FIGS. 5, 8, 12, 13 and 14 . The controller  14  may comprise: control circuitry; and/or processor circuitry; and/or at least one application specific integrated circuit (ASIC); and/or at least one field programmable gate array (FPGA); and/or single or multi-processor architectures; and/or sequential/parallel architectures; and/or at least one programmable logic controllers (PLCs); and/or at least one microprocessor; and/or at least one microcontroller; and/or a central processing unit (CPU); and/or a graphics processing unit (GPU), to perform the methods. 
     In various examples, the controller  14  may comprise at least one processor  24  and at least one memory  26 . The memory  26  stores a computer program  28  comprising computer readable instructions that, when read by the processor  24 , causes performance of the methods described herein, and as illustrated in  FIGS. 5, 8, 12, 13 and 14 . The computer program  28  may be software or firmware, or may be a combination of software and firmware. 
     The controller  14  may be part of the inspection device  20 , an ‘edge’ computer or a remote computer (such as a high-performance computing cluster in the ‘cloud’). Alternatively, the controller  14  may be distributed between a plurality of devices and locations. For example, the controller  14  may be distributed between the inspection device  20  and an ‘edge’ computer or may be distributed between the inspection device  20  and a high-performance computing cluster in the ‘cloud’. 
     The processor  24  may include at least one microprocessor and may comprise a single core processor, may comprise multiple processor cores (such as a dual core processor or a quad core processor), or may comprise a plurality of processors (at least one of which may comprise multiple processor cores). 
     The memory  26  may be any suitable non-transitory computer readable storage medium, data storage device or devices, and may comprise a hard disk and/or solid-state memory (such as flash memory). The memory may be permanent non-removable memory or may be removable memory (such as a universal serial bus (USB) flash drive or a secure digital card). The memory may include: local memory employed during actual execution of the computer program; bulk storage; and cache memories which provide temporary storage of at least some computer readable or computer usable program code to reduce the number of times code may be retrieved from bulk storage during execution of the code. 
     The computer program  28  may be stored on a non-transitory computer readable storage medium  30 . The computer program  28  may be transferred from the non-transitory computer readable storage medium  30  to the memory  26 . The non-transitory computer readable storage medium  30  may be, for example, a USB flash drive, an external hard disk drive, an external solid-state drive, a secure digital (SD) card, an optical disc (such as a compact disc (CD), a digital versatile disc (DVD) or a Blu-ray disc). In some examples, the computer program  28  may be transferred to the memory  26  via a signal  32  (which may be a wireless signal or a wired signal). 
     Input/output devices may be coupled to the controller  14  either directly or through intervening input/output controllers. Various communication adaptors may also be coupled to the controller  14  to enable the apparatus  10  to become coupled to other apparatus or remote printers or storage devices through intervening private or public networks. Non-limiting examples include modems and network adaptors of such communication adaptors. 
     The user input device  16  may comprise any suitable device or devices for enabling a user to at least partially control the apparatus  10 . For example, the user input device  16  may comprise one or more of a keyboard, a keypad, a touchpad, a touchscreen display, and a computer mouse. The user input device  16  may be part of, or a peripheral of, the inspection device  20 , an ‘edge’ computer or a remote computer (for example, a computer in the ‘cloud’ which is located in another city or country). The controller  14  is configured to receive signals from the user input device  16 . 
     The display  18  may be any suitable display for conveying information to an operator. For example, the display  18  may be a liquid crystal display, a light emitting diode display, an active matrix organic light emitting diode display, or a thin film transistor display, or a cathode ray tube display. The display  18  may be part of, or a peripheral of, the inspection device  20 , an ‘edge’ computer, or a remote computer (for example, a computer in the ‘cloud’ which is located in another city or country). The controller  14  is arranged to provide a signal to the display  18  to cause the display  18  to convey information to the user. 
     The inspection device  20  may be separate to the engine  12  and may be inserted into the engine  12  to inspect the engine  12 . For example, the inspection device  20  may be a borescope comprising a flexible tube (such as a snake arm), where the sensor  22  is mounted at one end of the flexible tube, and the display  18  is mounted at the opposite end of the flexible tube. Alternatively, the inspection device  20  may be embedded within the engine  12  and positioned to inspect the engine  12  at one or more locations. The controller  14  may be configured to control the operation of the inspection device  20 . For example, where the inspection device  20  is a robot, the controller  14  may be configured to control the position and pose of the inspection device  20  within the engine  12 . 
     The sensor  22  is configured to generate three-dimensional data and may comprise a structured-light three-dimensional scanner, stereo cameras or any other suitable apparatus. The sensor  22  may also be configured to generate two-dimensional data and may comprise a camera (for example, a charge-coupled device (CCD) or a complementary metal-oxide-semiconductor (CMOS)). Consequently, in some examples, the sensor  22  may comprise a structured-light three-dimensional scanner for generating three-dimensional data, and a camera for generating two-dimensional data. 
     Where the sensor  22  comprises a three-dimensional scanner (such as a structured light sensor) and a camera, the memory  26  also stores a transformation algorithm  29  that enables conversion between coordinates in the two-dimensional data generated by the camera, and coordinates in the three-dimensional data generated by the three-dimensional scanner. For example, a transformation algorithm  29  may be generated by the controller  14  for each image and point cloud that is received by the controller  14  (using triangulation and calibration parameters) and which enables conversion between a pixel location in the image file (such as a .jpg, .bmp or .raw file for example) and a point location in the point cloud data (such as a .csv file for example). 
     The engine  12  is associated with an aircraft  34  and is configured to generate propulsive thrust and/or electrical energy for the aircraft  34 . For example, the engine  12  may be a gas turbine engine such as a geared turbofan engine (as illustrated in  FIGS. 2, 3 and 4 ) or a ‘direct-drive’ turbofan engine (where a turbine is directly connected to a fan). Alternatively, the engine  12  may be a reciprocating engine, or an electrical motor. In some examples, the engine  12  may be system comprising a gas turbine engine or a reciprocating engine, and an electrical generator. In such a system, the output of the gas turbine engine or the reciprocating engine is connected to the electrical generator. 
     The engine  12  may be ‘associated’ with the aircraft  34  by being mounted on the aircraft  34  (usually referred to as ‘on-wing’). For example, the engine  12  may be mounted in or under a wing of the aircraft  34  or may be mounted within or on the fuselage of the aircraft  34 . Alternatively, the engine  12  may not be coupled to the aircraft  34 , but may be located at the same airport or repair facility as the aircraft  34  (usually referred to as ‘near-wing’). 
       FIG. 2  illustrates an example of a gas turbine engine  12  having a principal rotational axis  35  and comprising an air intake  36  and a propulsive fan  38  that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine  12  comprises a core  40  that receives the core airflow A. The engine core  40  comprises, in axial flow series, a low-pressure compressor  42 , a high-pressure compressor  44 , combustion equipment  46 , a high-pressure turbine  48 , a low-pressure turbine  50  and a core exhaust nozzle  52 . A nacelle  54  surrounds the gas turbine engine  12  and defines a bypass duct  56  and a bypass exhaust nozzle  58 . The bypass airflow B flows through the bypass duct  56 . The fan  38  is attached to and driven by the low-pressure turbine  50  via a shaft  60  and an epicyclic gearbox  62 . 
     In use, the core airflow A is accelerated and compressed by the low-pressure compressor  42  and directed into the high-pressure compressor  44  where further compression takes place. The compressed air exhausted from the high-pressure compressor  44  is directed into the combustion equipment  46  where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high-pressure and low-pressure turbines  48 ,  50  before being exhausted through the nozzle  52  to provide some propulsive thrust. The high-pressure turbine  48  drives the high-pressure compressor  44  by a suitable interconnecting shaft  64 . The fan  38  generally provides the majority of the propulsive thrust. The epicyclic gearbox  62  is a reduction gearbox. 
     An exemplary arrangement for a geared fan gas turbine engine  12  is shown in  FIG. 3 . The low-pressure turbine  50  (please see  FIG. 1 ) drives the shaft  60 , which is coupled to a sun wheel, or sun gear  66  of the epicyclic gear arrangement  62 . Radially outwardly of the sun gear  66  and intermeshing therewith is a plurality of planet gears  68  that are coupled together by a planet carrier  70 . The planet carrier  70  constrains the planet gears  68  to precess around the sun gear  66  in synchronicity whilst enabling each planet gear  68  to rotate about its own axis. The planet carrier  70  is coupled via linkages  72  to the fan  38  in order to drive its rotation about the engine axis  35 . Radially outwardly of the planet gears  68  and intermeshing therewith is an annulus or ring gear  74  that is coupled, via linkages  76 , to a stationary supporting structure  78 . 
     Note that the terms “low-pressure turbine” and “low-pressure compressor” as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan  38 ) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft  60  with the lowest rotational speed in the engine  12  (i.e. not including the gearbox output shaft that drives the fan  38 ). In some literature, the “low-pressure turbine” and “low-pressure compressor” referred to herein may alternatively be known as the “intermediate-pressure turbine” and “intermediate-pressure compressor”. Where such alternative nomenclature is used, the fan  38  may be referred to as a first, or lowest pressure, compression stage. 
     The epicyclic gearbox  62  is shown by way of example in greater detail in  FIG. 4 . Each of the sun gear  66 , planet gears  68  and ring gear  74  comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in  FIG. 4 . There are four planet gears  68  illustrated, although it will be apparent to the skilled reader that more or fewer planet gears  68  may be provided. Practical applications of a planetary epicyclic gearbox  62  generally comprise at least three planet gears  68 . 
     The epicyclic gearbox  62  illustrated by way of example in  FIGS. 3 and 4  is of the planetary type, in that the planet carrier  70  is coupled to an output shaft via linkages  72 , with the ring gear  74  fixed. However, any other suitable type of epicyclic gearbox  62  may be used. By way of further example, the epicyclic gearbox  62  may be a star arrangement, in which the planet carrier  70  is held fixed, with the ring (or annulus) gear  74  allowed to rotate. In such an arrangement the fan  38  is driven by the ring gear  74 . By way of further alternative example, the gearbox  62  may be a differential gearbox in which the ring gear  74  and the planet carrier  70  are both allowed to rotate. 
     It will be appreciated that the arrangement shown in  FIGS. 3 and 4  is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox  62  in the engine  12  and/or for connecting the gearbox  62  to the engine  12 . By way of further example, the connections (such as the linkages  72 ,  76  in the  FIG. 3  example) between the gearbox  62  and other parts of the engine  12  (such as the input shaft  60 , the output shaft and the fixed structure  78 ) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of  FIG. 3 . For example, where the gearbox  62  has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in  FIG. 3 . 
       FIG. 5  illustrates a first method of inspecting the engine  12  according to various examples. 
     At block  80 , the method includes inspecting the engine  12  during a first period of time to identify damage. In some examples, a human inspector may be at the same location as the engine  12  and may use a borescope (which may be the inspection device  20 , or may be a separate borescope) to inspect the components of the engine  12 . For example, a human inspector may use a borescope to inspect turbine blades of the high-pressure turbine  48  and/or the low-pressure turbine  50  of the gas turbine engine  12  illustrated in  FIG. 2  to identify damage. 
     As used herein, ‘damage’ includes any change to one or more components of the engine  12  that degrades the one or more components from their initial state, and which may adversely affect the current or future performance of the one or more components. Consequently, ‘damage’ includes, but is not limited to: loss of material from a component; changes to the shape of a component; and changes to the dimensions of a component. 
     It should be appreciated that the ‘first period of time’ is a period of time in which the engine  12  may be inspected ‘on-wing’ or ‘near-wing’. The aircraft  34  is not operational during the first period of time and is not cleared for flight by the control tower of the airport or repair facility. 
     At block  82 , the method includes receiving three-dimensional data of one or more components of the engine  12 . In some examples, the inspection device  20  may be inserted into the engine  12  and the controller  14  may receive three-dimensional data of one or more components of the engine  12  illustrated in  FIG. 2  from the sensor  22 . For example, the inspection device  20  may be inserted into the high-pressure turbine  48  of the gas turbine engine  12  and the controller  14  may receive three-dimensional data of the turbine blades of the high-pressure turbine  48 . 
     Where the sensor  22  comprises a structured-light sensor, the controller  14  may store the three-dimensional data in a row and column pixel order (XY order). In particular, the controller  14  may compute the three-dimensional coordinates of the pixels with projected light using triangulation and calibration parameters, and then store the three-dimensional coordinates in a .csv file using the XY order. 
     Where the sensor  22  comprises stereo cameras and generates two images, block  82  may further comprise converting the received two-dimensional data into three-dimensional data. In particular, the controller  14  may find corresponding pixel points between stereo images, and then compute three-dimensional coordinates using triangulation and calibration parameters. The controller  14  may then store the three-dimensional coordinates in a .csv file using a row and column pixel order (XY order). 
     Where the sensor  22  additionally comprises a two-dimensional sensor, block  82  may additionally comprise receiving two-dimensional data of the one or more components of the engine  12 . The use of this two-dimensional data is described in detail later with reference to  FIGS. 12, 13 and 14 . 
     At block  84 , the method includes determining, during the first period of time, whether the identified damage exceeds a threshold. In some examples, the human inspector may determine, using their experience and knowledge, whether the identified damage is acceptable or not for operation on the aircraft  34 . For example, where the human inspector identifies damage to turbine blades of the high-pressure turbine  48  at block  80 , he or she may, at block  84 , determine whether the identified damage is acceptable or not for operation using his or her experience and knowledge. 
     At block  86 , the method includes providing instructions to release the aircraft for operation in a second period of time, subsequent to the first period of time, if the identified damage does not exceed the threshold. In some examples, the human inspector may provide instructions to enable the control tower to release the aircraft  34  for operation in a second period of time. For example, where the human inspector determines, at block  84 , that the identified damage to the turbine blades of the high-pressure turbine  48  is acceptable for operation, he may provide instructions to enable the aircraft  34  to be released for operation. 
     It should be appreciated that the ‘second period of time’ is a period of time in which the engine  12  and the aircraft  34  are operational and cleared for flight by the control tower of the airport. Consequently, the second period of time may include one or more periods of time in which the aircraft  34  is airborne and in which the aircraft  34  may be carrying humans and/or cargo. 
     At block  88 , the method includes inspecting the received three-dimensional data during the second period of time to measure damage received by the one or more components. Block  88  may be performed by the controller  14 . In some examples, block  88  is performed automatically by the controller  14  in response to receiving the three-dimensional data. In other examples, a human operator may initiate the inspection of the received three-dimensional data by operating the user input device  16  and block  88  may be performed by the controller  14  in response to receiving a signal from the user input device  16 . 
     Block  88  may be performed in accordance with any of the methods illustrated in  FIGS. 8, 12, 13 and 14  and these are described in detail later in the detailed description. Furthermore, blocks  80 ,  84  and  86  may be performed by the controller  14  in some examples. 
       FIG. 6  illustrates a time line diagram of the first method of inspecting an engine. The time line diagram comprises a horizontal axis  90  for time and blocks  80 ,  82 ,  84 ,  86  and  88  positioned along the horizontal axis  90 . The first period of time is defined between a time t 0  and a time t 1 . The second period of time is defined between time t 1  and t 3 . A third period of time is defined from time t 3  and is a period of time in which the engine  12  may once again be inspected ‘on-wing’ or ‘near-wing’. Similar to the first period of time, the aircraft  34  is not operational during the third period of time and is not cleared for flight by the control tower of the airport or repair facility. 
     The inspection of the received three-dimensional data may be performed during a predetermined period of time from release of the aircraft  34  for operation. For example, the controller  14  may be configured to complete block  88  within a period of time defined between time t 1  and time t 2  (where time t 2  is after time t 1 , but before time t 3 ). 
     The first period of time and the second period of time are illustrated in  FIG. 6  to have a similar duration to aid clarity of the figure. It should be appreciated that in most instances, the second period of time is longer than the first period of time. 
     The first method may be advantageous in that the aircraft  34  may be released for operation earlier than in current methods. In particular, block  80  may be performed relatively quickly because the human inspector may not carry out detailed measurements on the components of the engine  12  (for example, creep of turbine blades) and where they do not determine damage above a threshold at block  84 , they may instruct the aircraft  34  to be released for operation. The detailed measurements on the components of the engine  12  may be performed by the controller  14  during the second period of time when the aircraft  34  is operational, and may even be in flight. Consequently, the first method may reduce aircraft on ground (AOG) time due to inspection. 
       FIG. 7  illustrates a time line diagram of a second method of inspecting the engine  12 . The time line diagram of  FIG. 7  is similar to the time line diagram of  FIG. 6  and where the features are similar, the same reference numerals are used. 
     The method illustrated in  FIG. 7  differs from the method illustrated in  FIG. 6  in that block  88  is performed and completed during the first period of time and prior to block  86 . For example, the controller  14  may inspect the received three-dimensional data to measure the damage received by one or more components of the engine  12  in response to receiving the three-dimensional data at block  82 , or may inspect the received three-dimensional data to measure damage received by one or more components of the engine  12  in response to receive a signal from the user input device  16 . 
     The method illustrated in  FIG. 7  also differs from the method illustrated in  FIG. 6  in that block  86  is only performed when it is determined, at blocks  84  and  88 , that the damage is below acceptable thresholds of damage. 
     Similar to  FIG. 6 , the first period of time and the second period of time are illustrated in  FIG. 7  to have a similar duration to aid clarity of the figure. It should be appreciated that in most instances, the second period of time is longer than the first period of time. 
     The second method may be performed when the controller  14  has sufficient computing resources and availability to enable block  88  to be performed within an acceptable period of time from the receipt of the three-dimensional data at block  82 . For example, the controller  14  may select between the first method and the second method by assessing what computing resources are available upon receipt of the three-dimensional data at block  82  and determine whether block  88  may be performed within a predetermined period of time. Where the controller  14  determines that block  88  may be performed within the predetermined period of time, the controller  14  may perform the second method. Where the controller  14  determines that block  88  may not be performed within the predetermined period of time, the controller  14  may perform the first method. 
     The method illustrated in  FIG. 7  is advantageous in that block  88  may be performed relatively quickly by the controller  14  during the first period of time and thus provide a quick and accurate inspection prior to the aircraft  34  being released for operation. 
       FIG. 8  illustrates a flow diagram of a third method of inspecting the engine  12 . The third method may be performed in block  88  illustrated in  FIGS. 5, 6 and 7 . 
     At block  92 , the method includes identifying a feature of the component using the received three-dimensional data. As used herein, the word ‘feature’ includes any change to the component that degrades the component from its initial state (that is, the ‘feature’ is some form of damage and may also be referred to as a ‘damage feature’).  FIGS. 9, 10 and 11  illustrate three examples of such ‘features’ of a turbine blade and are described in the following paragraphs in more detail. It should be appreciated that these examples are not exhaustive, and a turbine blade may have different features. Also, it should be appreciated that other types of components may have different features to those illustrated in  FIGS. 9, 10 and 11 . 
       FIG. 9  illustrates a side view of a turbine blade  94  according to a first example. The turbine blade  94  comprises a platform  96 , an aerofoil  98 , and a shroud  100 . The aerofoil  98  defines a plurality of cooling holes  102  and has a leading edge  104  and a trailing edge  106 . The turbine blade  94  comprises a feature  108  which is, in this example, a crack that extends between adjacent cooling holes  102  near the leading edge  104  of the aerofoil  98 . The measurable dimensions of the crack  108  include length, width and depth. 
       FIG. 10  illustrates a side view of a turbine blade  110  according to a second example. The turbine blade  110  is similar to the turbine blade  94  and where the features are similar, the same reference numerals are used. 
     The turbine blade  110  comprises a feature  112  which is, in this example, erosion that extends along the leading edge  104  and towards the trailing edge  106 . The erosion  112  is defined by the removal of surface material of the turbine blade  94  and may include a plurality of cavities  114  that extend into the aerofoil  98 . The measurable dimensions of the erosion  112  include length, width, surface area of erosion, and depth of the eroded area relative to an uneroded area. 
       FIG. 11  illustrates a side view of a turbine blade  116  according to a third example. The turbine blade  116  is similar to the turbine blades  94  and  110  and where the features are similar, the same reference numerals are used. 
     The turbine blade  116  comprises a feature  118  which is, in this example, creep of the turbine blade  116 . The creep  118  may be defined by the elongation of the aerofoil  98  and may be measured by measuring the distance L 1  between the platform  96  and the shroud  100  at the trailing edge  106  and subtracting the distance L 2  of the aerofoil  98 . L 2  may be the distance between the platform  96  and the shroud  100  after manufacture of the turbine blade  116 , but before use of the turbine blade  116  in the engine  12  (that is, the initial state of the turbine blade  116 ). Alternatively, L 2  may be the designed distance between the platform  96  and the shroud  100  (that is, the distance in the computer aided design (CAD) model of the turbine blade  116 ). 
     The creep  118  may additionally or alternatively be defined by the aerofoil  98  twisting through an angle about the longitudinal axis of the turbine blade  116  (where the longitudinal axis extends between, and is perpendicular to, the platform  96  and the shroud  100 ). 
     Returning to  FIG. 8 , in some examples, the feature to be identified may be predetermined by the controller  14 . In other words, the controller  14  may be pre-configured to identify a feature of the component and the controller  14  requires no further input to determine the feature to be identified. In other examples, the controller  14  may control the display  18  to display a plurality of features and a user may operate the user input device  16  to select one or more of the displayed features to be identified. 
     The controller  14  may use any suitable method or methods for identifying a feature. For example, the controller  14  may use any one or more of: CAD alignment/registration, Procrustes analysis, iterative closest point (IPC) registration, random sample consensus (RANSAC), plane matching, point cloud segmentation, and machine learning to identify a feature. 
     At block  120 , the method includes determining coordinates of the identified feature in the three-dimensional data. In some examples, the controller  14  may determine the coordinates of the identified feature by determining the coordinates of the perimeter of the identified feature in the received three-dimensional data. 
     At block  122 , the method includes measuring a parameter of the feature of the component using the determined coordinates of the feature in the three-dimensional data. As used herein, a ‘parameter’ includes physical dimensions of a feature (length, width and so on for example), the number of features, the density of features, and the spacing between features. In some examples, block  122  may include measuring a plurality of parameters of the feature using the determined coordinates of the feature in the three-dimensional data. 
     The controller  14  may measure at least one of: one or more angles, one or more lengths, an area, a volume of the identified feature, the number of identified features, the density of identified features, and the spacing between features, using the determined coordinates. In order to perform the measurement(s), the controller  14  may perform point cloud processing (such as RANSAC, three-dimensional object matching), CAD alignment with a model of the component, and/or point cloud stitching. 
     Taking  FIG. 9  as an example, the controller  14  may use the determined coordinates of the crack  108  to measure the length, the width and the depth of the crack  108  in the aerofoil  98 . Considering  FIG. 10 , the controller  14  may use the determined coordinates of the eroded portion  112  to measure the surface area and depth of the eroded portion  112  of the aerofoil  98 . The controller  14  may also use the determined coordinates to determine the depth and diameter of the cavities  114 . Turning to  FIG. 11 , the controller  14  may use the determined coordinates to measure the length L 1  and then determine the creep of the turbine blade  116  by subtracting L 2  from L 1 . 
     At block  122 , the method may additionally include controlling storage of the measured parameter or parameters in a dataset  123  in the memory  26 . 
       FIG. 12  illustrates a flow diagram of a fourth method of inspecting the engine  12 . The controller  14  may perform the fourth method where the sensor  22  comprises a two-dimensional sensor and a three-dimensional sensor. The fourth method illustrated in  FIG. 12  is similar to the first method illustrated in  FIG. 5  and to the third method illustrated in  FIG. 8  and where the blocks are similar, the same reference numerals are used. 
     At block  82 , the method includes receiving data comprising two-dimensional data and three-dimensional data of one or more components of the engine  12 . For example, the controller  14  may receive a .jpg file (two-dimensional data) from a camera of the sensor  22  of one or more components of the engine  12  and a .csv file (three-dimensional data) from a structured light sensor of the sensor  22  of the same one or more components of the engine  12 . 
     At block  124 , the method includes identifying a feature of the one or more components using the two-dimensional data. For example, the controller  14  may use any suitable technique for identifying a feature in the .jpg file received at block  82 . Suitable techniques include correlation, matching, texture analysis, and artificial intelligence (a deep learning neural network for example). 
     At block  126 , the method includes determining coordinates of the identified feature in the two-dimensional data. For example, the controller  14  may determine the coordinates of each pixel of the feature identified in block  124  in the .jpg file. 
     At block  128 , the method includes determining coordinates of the identified feature in the received three-dimensional data using: the determined coordinates of the identified feature in the two-dimensional data; and the predetermined transformation algorithm  29 . For example, the controller  14  may calculate the coordinates of the identified feature in the received three-dimensional data by applying the transformation algorithm  29  to the two-dimensional coordinates of the feature determined at block  126 . 
     The fourth method then moves to block  122  and includes measuring one or more parameters of the identified feature of the component using the coordinates of the identified feature in the three-dimensional data. The fourth method may also include controlling storage of the measured one or more parameters at block  122 . 
     The fourth method may be advantageous where the controller  14  has a higher probability of identifying a feature in the two-dimensional data than in the three-dimensional data. For example, some features (such as erosion) may be relatively challenging for the controller  14  to identify in the three-dimensional data because the change in coordinates (relative to the original state of the component) may be small. However, such features may readily identifiable in the two-dimensional data by the controller  14  due to a change in colour or pattern. 
       FIG. 13  illustrates a flow diagram of a fifth method of inspecting the engine  12 . The fifth method is similar to the first method illustrated in  FIG. 5 , the third method illustrated in  FIG. 8 , and the fourth method illustrated in  FIG. 12 , and where the blocks are similar, the same reference numerals are used. 
     At block  82 , the fifth method includes receiving data comprising two-dimensional data and three-dimensional data of the component of the engine  12 . The fifth method then moves to block  92  and includes identifying a feature of the component of the engine  12  using the received three-dimensional data. 
     At block  130 , the fifth method includes determining coordinates in the three-dimensional data of a first volume bounding the coordinates of the feature. In some examples, the first volume may be defined by the three-dimensional perimeter of the identified feature. In other examples, the first volume may be defined by a three-dimensional region of interest which encompasses the three-dimensional coordinates of the identified feature. The region of interest may be identified using a three-dimensional (CAD) model of the component stored in the memory  26  to assist in the identification of the sub-component that comprises the identified feature. 
     The fifth method then moves to block  132  and includes determining coordinates of a first area in the two-dimensional data corresponding to the first volume using: the determined coordinates of the first volume in the three-dimensional data; and the predetermined transformation algorithm  29 . For example, the controller  14  may calculate the coordinates of the first area by applying the transformation algorithm  29  to the determined coordinates of the first volume. 
     At block  134 , the fifth method includes identifying a feature of the component using a subset of the two-dimensional data corresponding to the first area. For example, where the two-dimensional data received at block  82  comprises a 1920 pixel by 1080 pixel image and the feature is erosion, the subset of data corresponding to the first area has coordinates of 200 to 500 on the horizontal (X) axis and coordinates of 600 to 800 on the vertical axis (Y). The controller  14  may perform feature analysis and identification as described above with reference to block  124  on this subset of the two-dimensional data. 
     It should be appreciated that block  134  is likely to identify the same feature as the feature identified at block  92 , but may identify additional features since the analysis is performed on two-dimensional data, whereas block  134  is performed on three-dimensional data. For example, the controller  14  may identify an eroded portion  112  of an aerofoil  98  at block  92 , and may identify the eroded portion  112  and a crack at block  134 . 
     The fifth method then moves to block  126  and includes determining coordinates of the feature identified at block  134  in the two-dimensional data. 
     At block  128 , the fifth method includes determining coordinates of the feature identified at block  134  in the three-dimensional data using: the coordinates of the feature in the two-dimensional data determined at block  126 ; and the predetermined transformation algorithm  29 . 
     The fifth method then moves to block  122  and includes measuring one or more parameters of the feature identified at block  134  using the three-dimensional coordinates of the feature determined at block  128 . The fifth method may also comprise controlling storage of the measured one or more parameters at block  122 . 
     The fifth method may advantageously increase the probability of identifying a feature of a component of the engine  12  because feature analysis and identification is performed on both the two-dimensional data and three-dimensional data received at block  82 . 
       FIG. 14  illustrates a sixth method of inspecting the engine  12 . The sixth method is similar to the first method illustrated in  FIG. 5 , the third method illustrated in  FIG. 8 , the fourth method illustrated in  FIG. 12 , and the fifth method illustrated in  FIG. 13  and where the blocks are similar, the same reference numerals are used. 
     At block  82 , the method includes receiving data comprising two-dimensional data and three-dimensional data of the engine  12 . 
     The sixth method then moves to block  136  and includes identifying a second area using the two-dimensional data of the component of the engine  12 . The second area excludes predetermined components and/or predetermined sub-components of the engine  12  within the two-dimensional data. For the example, the controller  14  may be configured to identify cracks  108  in the aerofoil  98  (either pre-configured or user-configured as described above) and may exclude the platform  96  and the shroud  100  (which are sub-components of the turbine blade  94 ,  110 ,  116 ). Where the two-dimensional data comprises data on other components (such as a stator blade for example), the controller  14  may exclude such components from the second area at block  136 . 
     At block  138 , the sixth method includes determining coordinates of a second volume in the three-dimensional data corresponding to the second area using: the determined coordinates of the second area in the two-dimensional data; and the predetermined transformation algorithm  29 . For example, the controller  14  may apply the transformation algorithm  29  to the two-dimensional coordinates of the second area determined at block  136  to calculate the coordinates of the second volume in the three-dimensional data. 
     The sixth method then moves to block  140  and includes identifying a feature of the component using a subset of the three-dimensional data corresponding to the second volume calculated at block  138 . It should be appreciated that block  140  is similar to block  92  in the third method illustrated in  FIG. 8  and in the fifth method illustrated in  FIG. 13 , but differs in that feature analysis and identification is only performed on a subset of the three-dimensional data (that is, the three-dimensional data that corresponds to the second volume). 
     The sixth method then moves through blocks  130 ,  132 ,  134 ,  126 ,  128  and  122  to provide a measurement of one or more parameters of the identified feature of the component. The sixth method may also include controlling storage of the measured one or more parameters at block  122 . 
     The sixth method may be advantageous in that the analysis of the two-dimensional data to remove irrelevant data (at blocks  136  and  138 ) may increase the efficiency of the analysis of the three-dimensional data (at block  140 ). This may reduce the time taken by the controller  14  to perform block  140 , and/or may enable a reduction in the use of the computational resources of the controller  14 . 
     The methods illustrated in  FIGS. 8, 12, 13 and 14  may be advantageous in that the stored measured parameter or parameters  123  may be used to determine the condition of a component and schedule the next inspection (and potential repair or replacement) of the component. 
     It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. For example, the different embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment containing both hardware and software elements. 
     The methods illustrated in  FIGS. 8, 12, 13 and 14  are described above in terms of identifying and measuring a single feature of a single component. It should be appreciated that these methods may also be used to identify and measure a plurality of features on a single component. Furthermore, these methods may be used to identify a plurality of features across a plurality of components (where a single component may have one or more features). 
     In some examples, block  82  may only comprise receiving two-dimensional data of one or more components of the engine  12 , and block  88  comprises inspecting the received two-dimensional data during the second period of time to measure damage. In these examples, the controller  14  may use the techniques mentioned above with reference to block  124  to identify one or more features in the two-dimensional data and may measure one or more parameters of those features using the two-dimensional data. 
     In some examples, the method illustrated in  FIG. 5  and described above may be performed for engines that are not associated with an aircraft (such industrial gas turbines). In these examples, the first period of time is an inspection phase for the engine (where the engine is non-operational), and the second period of time is an operational phase for the engine. Furthermore, the method illustrated in  FIG. 5  may be performed for any industrial system (an oil and gas facility for example) where the first period of time is an inspection phase for the industrial system (where the industrial system is non-operational), and the second period of time is an operational phase for the industrial system. 
     Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.