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S8C13 - CONDITION MONITORING PROGRAMS FOR PROPULSION SYSTEMS
Table of Contents
A. SOA Program
B. WDA Guidance
1. A Condition Monitoring (CM) program is a coordinated activity that constantly or periodically collects data that can be used to trend and indicate machine condition or ‘health’ against an acceptable limit, prior to in-service failure. Proper analysis and trending of CM data can minimise in-service failures, thereby assuring technical airworthiness, improving reliability, availability and minimising maintenance and logistics costs. An effective CM program forms a key part of a Reliability, Availability and Maintainability (RAM) program. As required of DEFLOGMAN Part 2 Vol 10 Chap 14 - Materiel Reliability, Availability and Maintainability Policy, the Australian Defence Organisation (ADO) has a responsibility to ensure that RAM is applied to all phases of the materiel life cycle in the interest of achieving readiness and sustainability objectives at minimum cost of ownership.
2. Mechanical systems can provide indications of gradual failure modes, which can be trended with time and usage through CM tasks. CM tasks can also be referred to as ‘on-condition’ tasks, which support a preventive maintenance program, refer AAP 7001.038—Maintenance Requirements Determination (MRD) Manual. The contents of this chapter are applicable to any aircraft mechanical system that has CM techniques prescribed by the Original Equipment Manufacturer (OEM) or warrant the introduction of a CM program to manage gradual failure modes. In the context of a CM program, the propulsion system should include the transmission system for helicopter aircraft.
3. In general, propulsion system OEMs do not evaluate the effectiveness of their prescribed CM techniques. Therefore ADF assurance of the effectiveness of CM programs from an economic and technical airworthiness perspective is required. An effective CM program requires five distinct phases that operate in a continuous cycle as follows:
4. A CM program is a progressive pro-active maintenance philosophy based on a process of regular data collection and trending that identifies emerging fault trends as mechanical systems gradually wear during service. As such, the process of data collection needs to be regular, efficient and effective for the program to be easily implemented and of maximum benefit. For systems that are maintained using fixed scheduled servicing, CM data can also be used to justify maintenance extensions when limits are being met. Since an effective CM program can avoid costly in-service failures that generate unscheduled major repairs and be used to justify maintenance extensions, there is the potential for significant cost savings in spare parts and maintenance costs.
5. To ensure gas turbine Engine Structural Integrity (ESI), TAREG 3. 5. 5—Engine Structural Integrity Management requires effective CM programs for gas turbine engines to be documented in either a CM Program Plan (CMPP) or in a section of the ESI Management Plan (ESIMP). Refer to AAP 7001.054—Electronic Airworthiness Design Requirements Manual for guidance on document formats for CMPPs and ESIMPs. For propulsion systems fitted to rotary wing aircraft, the CMPP needs to capture CM requirements for the gas turbine and transmission system (TX).
6. This chapter prescribes the Approved Maintenance Organisation (AMO) responsibilities and requirements for the development and implementation of effective CM programs for propulsion systems.
7. Each CM program and the associated data collection and trend analysis intervals will depend on specific configurations and failure modes. A useful source of generic guidance for rotating machinery is the ABR 6140—Condition Monitoring Manual.
8. The CM Program Plan needs to describe the configuration of the system being monitored. In particular, it should include the lubrication system and any Maintainability features that the OEM may have included during design such as magnetic chip detectors, boroscope inspection ports and hard-wired accelerometers. To support the lubrication system description, a Propulsion System Metal Map (PSMM) is important to document the material that each oil wetted component is made of to enable the respective AMO or SPO to identify the origin of collected wear debris.
9. The CM techniques recommended by an OEM or introduced by the ADF need to be applicable to specific failure modes that the propulsion system is known to be prone to. Failure modes should be identified by the OEM during the design phase through a Failure Modes Effects and Criticality Analysis (FMECA). The CMPP should describe the systems being monitored and identify the applicable failure modes. Additionally, the applicable CM techniques should be identified against each failure mode. Additional failure modes are likely to evolve in service, particularly if the usage is different to the OEM design assumptions. Typical failure modes for propulsion systems include, but are not limited to;
CONDITION MONITORING TECHNIQUES
10. CM techniques are recommended by the OEM at the time of service introduction or can be introduced by the ADF should OEM-recommended techniques become outdated or ineffective. CM techniques typically used on ADF propulsion systems include, but are not limited to:
11. The applicability of these techniques will depend on the system design, typical failure modes and OEM recommendations. PM is typically required for all applications as a matter of course, but OEMs rarely mandate trending of data. Hence, the ADF needs to consider OEM-recommended maintenance activities as a bare minimum and evaluate the effectiveness of these activities in service.
12. SOA and WDA are useful for monitoring the levels of foreign material suspended within a lubricating oil system. Foreign materials can be produced by:
13. Oil debris analysis is achieved by qualitative and/or quantitative evaluation of the debris collected. SOA can be used to evaluate minuscule debris (up to 10 microns in diameter). WDA can be used to analyse debris collected by Magnetic Chip Detectors (MCD) and oil filters, ie typically greater than 15 microns in diameter.
14. A single CM technique should not be used in isolation to determine engine serviceability. For example, turbine degradation may be indicated by PM data but should be further confirmed through RVI before embarking upon an expensive Hot Section Inspection or Bay Service (BS). Increasing SOA trends can be complemented by WDA. For rotary wing aircraft engaged in ship-borne operations, it may be prudent to perform more regular WDA and VA whilst SOA samples are being processed at land-based facilities.
15. For a specific CM program, the applicable techniques should be summarised in a table in the CMPP, which includes the intervals at which CM data is collected and the applicable special servicing number. Regular CM activities should appear as special ‘S’ servicing in the applicable Technical Maintenance Plan (TMP) to provide clear visibility of the implementation and reporting requirements.
16. Further details on SOA Programs (including equipment correlation and calibration), WDA, VA and PM are contained in Annexes A to D respectively. Note that commercial and military laboratories participating in ADF aviation SOA Programs are to calibrate and correlate their equipment in accordance with Annex A.
Oil Condition Analysis
17. Oil condition analysis refers to assessing the chemical and physical properties of the oil (rather than the entrained particulate). The condition of the oil is important as it directly influences the ability of the oil to perform functions such as lubrication and protection against corrosion. Deterioration of the oil condition can lead to problems such as corrosion and accelerated wear of components. As a minimum requirement, lubrication oils should be monitored for water content and viscosity. Where gas turbine lubricating oils pass through an oil/fuel heat exchanger, the lubricating oil should be monitored for fuel dilution.
18. Another valuable parameter that can be monitored is the Total Acid Number (TAN). TAN gives an indication of the potential of the oil to corrode unprotected metal surfaces, such as the internal surfaces of gearboxes.
19. Fourier Transform Infrared (FTIR) Spectroscopy can be used to provide most oil condition measurement parameters including those mentioned above. The FTIR emits an absorbency spectrum of the individual organic compounds within an oil sample. This spectrum can be compared to new oil or established parameters. Oil anomalies evaluated by FTIR include:
Remote Visual Inspection
20. Using videoscope equipment a RVI can be carried out by feeding optical fibre scopes through dedicated inspection ports or other means of access such as the engine inlet, engine exhaust, removal of fuel nozzles or removal of igniter plugs. It is the least scientific and yet the most effective at confirming damage, providing that state of the art videoscope equipment is used and access can be gained to engine internals. Maintenance manuals for older aircraft types may refer to the use of outdated optical boroscope equipment that are ineffective. Ideally SPOs and AMOs should ensure that state of the art equipment is utilised when outdated and ineffective equipment is prescribed by the OEM.
21. Although not usually required as a matter of course, temperature monitoring can be achieved by using temperature sensitive labels which enables monitoring and measurement of temperatures in aircraft under operating conditions where instrumentation is impractical or unwarranted. The labels indicate a specific temperature or sequence of temperature measurements by a visual change of colour. The colour change is irreversible and the performance of the labels is not affected by transient contact with contaminants, eg solvents, fuels, or lubricants. Authorisation for use is vested with the applicable SPO.
22. The installation and removal of any equipment required to perform CM (such as vibration analysers or videoscope equipment) is to be annotated in the recording and certification system and transferred to the Change of Configuration Section (CCS) in accordance with the systems approved instructions.
23. Where there is also the requirement to perform in-flight data collection, eg for PM or VA, the requirement is to be annotated in recording and certification system and transferred to the Special Maintenance Requirement (SMR) section of the recording and certification system in accordance with the systems approved instructions.
CONDITION MONITORING TRAINING AND AUTHORISATION
24. Operators of CM equipment are to be trained and authorised. Approved ADF courses for CM operators include the WDA and SOA Program (SOAP) courses and any training provided by CM equipment OEMs or propulsion system OEMs. ADF WDA and SOAP training is to be conducted in two phases as follows:
Condition Monitoring Operator Authorisation
25. The CM supervisor is responsible for authorising suitably trained technicians as CM operators once satisfied that CM duties could be performed unsupervised. Completed successful training is to be reflected in the respective CM Operators record of training and employment document in accordance with local AMO procedures. NDT&CT maintains a register of qualified CM Operators (for WDA and SOAP only) and is to be notified when OJE is complete.
Condition Monitoring Supervisor Authorisation
26. CM supervisors are specialised on aircraft Oil Debris Analysis programs on which they have gained CM operator experience. The time required for a CM operator to gain the necessary experience before progressing to CM supervisor depends on the individual and is determined by the appropriate AMO authority, typically the OIC of the respective CMC. A period no less than twelve months is recommended. CM supervisor may perform CM Operator duties and manage CMCs. CM supervisors are authorised in their qualification records in accordance with local AMO procedures.
27. NDT&CT can provide informal training on the use of SEM–EDX equipment. The Defence Science and Technology Organisation (DSTO) Platform Sciences Laboratory (PSL) can provide informal training in PM and VA upon request, through DAVENG–DGTA.
28. Funding for all CM related training is the responsibility of the respective AMO and SPO.
CONDITION MONITORING DATA MANAGEMENT
29. CM data needs to be collected analysed and stored for future trending and health/condition assessment. To rationalise this activity at a particular base, it may be prudent to have a central Condition Monitoring Centre (CMC) which can then provide advice to AMOs and SPOs regarding the condition of propulsion systems in operation.
30. The aircraft Planned Servicing Schedule (PSS) and maintenance publications are to specify under what circumstances CM data is to be collected. CM data is normally required:
31. In consultation with each other, the responsible SPO, AMOs and CMCs are to develop and promulgate approved procedures either in local instructions or in the relevant PSS for the collection of CM data. The procedures will need to be more elaborate for WDA and SOA programs to ensure that samples are not contaminated. Procedures should detail:
32. Data format may vary from hardcopy forms with manually recorded results to electronic databases that can also trend results. CM data may include, but not be limited to:
33. Deeper maintenance facilities (government and contractor) shall produce CM reports to support the post mortem phase of the CM philosophy. Recurring faults may warrant technical build improvement/modification to reduce maintenance costs and improve system reliability.
34. As a minimum, all CM data shall be recorded with the following generic information:
35. CM data should be collated against each propulsion system serial number and stored on a specific engine/TX file. Electronic databases should be employed where possible to make the data collection and trending process as efficient as possible. A central agency at the aircraft SPO should also keep copies of engine/TX files containing CM data so that the SPO has a fleet-wide perspective of propulsion system ‘health’. If there is a concern about the accuracy of a result, eg unusually high trends, check samples (for SOA and WDA) should be taken and processed in a timely manner to support engineering decisions.
CONDITION MONITORING ALERT LEVELS AND CODES
36. CM alert levels are either defined by the OEM in maintenance manuals or may need to be developed locally based on in-service experience. Alert levels are used to indicate when more detailed analysis is required, such as forwarding WDA samples for SEM–EDX analysis. The alert level may also dictate more stringent monitoring by reducing the normal CM data collection interval. Ideally, more stringent monitoring will enable faults to be managed before in-service failure. The following alert levels can be used to manage CM data collection and analysis:
37. Alert levels for some techniques may be objective in that they are based on discrete data (eg ppm limits for SOA, temperature and pressure limits for PM, vibration amplitude for VA). Qualitative WDA is a more subjective technique that will not include discrete data but will require a subjective assessment of the debris morphology (size, shape, markings and colour). Quantitative WDA may require the use of specific levels based on debris quantity per hour (DQ/HR), refer to Annex B for details.
38. Alert levels may include codes, which can serve as a status indicator for the various stages of failure mode progression. A description of this code system needs to be included in the respective CMPP. A recommended code system typically adopted for SOA and WDA programs is as follows:
39. SPOs are responsible for ensuring that alert levels and codes are applicable to ADF aircraft and CM equipment. This is particularly important for SOA programs, which may prescribe US Joint Oil Analysis Program (JOAP) limits that may not be applicable to ADF aircraft and SOAP equipment. NDT&CT–DGTA and DSTO–PSL can provide advice on the applicability of CM limits.
40. When analysing data, assurance checks should be applied when data appears uncharacteristic. Additionally, multiple techniques should be used to complement each other before deciding to remove propulsion systems based on the results of one technique.
41. To enable the responsible SPO to evaluate the effectiveness of their CM programs, whenever a defect report is raised for a propulsion system exceeding alert levels, the CMC is to provide the responsible SPO weapon system engineer with a copy of the relevant CM data and trending results.
42. CM data and trends should be able to assist management with prescribing a maintenance activity prior to in-service failure. Maintenance prescription may include removal of a system that is trending towards failure or the collection of more CM data over shorter intervals. The SMM or delegate at the applicable AMO is responsible for determining the serviceability of propulsion systems based on the assessment of all available technical information. The types of information may include but not be limited to:
CONDITION MONITORING PROGRAM REVIEWS
43. CM programs should be reviewed at least once every two years to confirm their effectiveness from a technical airworthiness and economic perspective. The applicable SPO is responsible for ensuring the effectiveness of respective CM programs through the monitoring of Key Performance Indicators (KPIs), reviewing of maintenance procedures, and CM data management. DSTO can provide advice for SPOs when reviewing the effectiveness of current programs.
Key Performance Indicators
44. The effectiveness of a CM program needs to be monitored to confirm that particular faults are being detected before in service failure or conversely, to confirm whether a particular technique is not useful and therefore causing unnecessary cost. Acceptable levels of performance need to be determined by the applicable SPO based on their experience with engine and TX reliability rates or based on OEM predicted Mean Time between Failure (MTBF) data. Metrics should be used to assess the Reliability, Availability and Maintainability of a propulsion system. These terms are defined in DEFLOGMAN - Glossary.
45. Some KPIs that can be used to provide an indication of CM program effectiveness from an economic and technical airworthiness perspective include, but are not limited to:
46. The applicable SPO should establish a baseline of KPI metrics based on in-service experience, Service Level Agreements, or contractual availability requirements. Where historical reliability data is unavailable, the SPO should begin a program of monitoring KPIs to determine an acceptable benchmark. For new acquisition aircraft, RAM performance requirements should be established by the applicable single service RAM Centre of Expertise and may include MTBF predictions from the OEM.
47. The effectiveness of a CM program requires the involvement and support of a number of ADF and contractor agencies. The responsibility of each specific agency needs to be clearly articulated in their CMPP.
Systems Program Office
48. The responsible SPO is the controlling authority for the CM Program and is responsible for:
Approved Maintenance Organisations
49. AMOs are responsible for:
Condition Monitoring Centres
50. For economic reasons, it may be more cost effective for CM data analysis to be centralised in an SPO or to be out-sourced to a specialist contractor. These centralised organisations and contractors are collectively referred to as Condition Monitoring Centres. CMCs are responsible for:
Directorate of Aviation Engineering
51. DAVENG–DGTA is responsible for:
Non-Destructive Testing and Composite Technologies
52. NDT&CT–DGTA is responsible for:
Defence Science and Technology Organisation
53. Defence Science and Technology Organisation–Platform Sciences Laboratory (DSTO–PSL) is responsible for:
Aerospace Materiel System Program Office
54. Aerospace Materiel System Program Office is responsible for:
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