| 1. |
- Ahmadi, Alireza, et al.
(author)
-
An overview of trends in aircraft maintenance program development : past, present, and future
- 2007
-
In: Risk, Reliability and Societal Safety. - London : Taylor and Francis Group. - 9780415447867 ; , s. 2067-2076
-
Conference paper (peer-reviewed)abstract
- The purpose of this paper is to describe the trends in aircraft maintenance program development during the last 50 years, including the reasons for the aircraft industry to change its view of maintenance. The major milestones and fundamental reasons for such development are also discussed and illustrated in relation to a flow diagram, which shows the logical and chronological order of the trends. Finally, the paper describes some possibilities and challenges as regards applying Information & Communication Technology (ICT) within the emerging approach of e-Maintenance in order to enhance the surveillance of aircraft maintenance program performance.
|
|
| 2. |
- Ahmadi, Alireza, et al.
(author)
-
Assessment of the cost of operational consequences of failures in aircraft operation
- 2007
-
In: Proceedings of 3rd International Conference on Reliability and Safety.
-
Conference paper (peer-reviewed)abstract
- Maintenance decisions regarding aircraft require consideration of the operational impact of failures. The cost of the operational impact of failure is difficult to assess due to the influence of a large number of contributory factors. This study attempts to assess the cost of operational consequences of failures using the expertise of the field experts following a pairwise contribution technique. The study shows that the proposed model can be a tool to assess the cost of operational consequences of failures in aircraft operation, when there is not sufficient and reliable data
|
|
| 3. |
|
|
| 4. |
- Ahmadi, Alireza, et al.
(author)
-
Risk based maintenance decision for periodically tested repairable components subject to hidden failure
- 2011
-
In: Proceedings of 2nd International Conference on Reliability, Safety and Hazard - ICRESH 2010. - Piscataway, NJ : IEEE Communications Society. - 9781424483440 - 9781424483433 ; , s. 197-204
-
Conference paper (peer-reviewed)abstract
- This paper aims to develop a graphical method to facilitate the identification of risk and cost of postponement of restoration for repairable components which are periodically tested and whose failures are hidden, i.e, are detectable by inspection or upon demand. The paper focuses on the items which are under aging, however, the methodology is flexible to implement for any aging pattern. The paper considers Failure Finding Inspection (FFI) with restoration actions (FFI+Res), for the “safety effect” categories of hidden failures. As-bad-as-old (ABAO) inspection effectiveness and as-good-as-new (AGAN) restoration effectiveness are considered. In case of repair due to findings by inspection, as-bad-as-old repair effectiveness is considered. The graphical methodology proposed in this paper considers inspection and repair times, as well as the costs associated with accident, inspection, repair, and restoration, and takes into account the opportunity losses due to the maintenance downtime. The analytical approach is based on the Mean Fractional Dead Time. In the case of an operational limit, when it is not possible to remove the unit for restoration, or one needs to use the unit longer than the expected operating time, the paper introduces an approach to analyzing the possibility of and conditions for providing an extension to the restoration interval that satisfies the risk constraints and the business requirements at the same time.
|
|
| 5. |
- Ahmadi, Alireza, et al.
(author)
-
Risk based maintenance deferral for components subject to hidden failure
- 2012
-
In: 2012 proceedings. - Piscataway, NJ : IEEE Communications Society. - 9781457718496
-
Conference paper (peer-reviewed)abstract
- In the aviation industry, it may be necessary to employ a combination of Failure Finding Inspection (FFI) and a scheduled discard task at a specific threshold, when a component is aging and its failures are hidden and exert a “safety effect”. This is to ensure an adequate level of availability of hidden functions, and to reduce the risk of multiple failures to an acceptable level. However, in some situations, operators prefer to extend the discard life of components beyond their recommended life limit, due to operational needs or logistic issues. This necessitates the definition of an optimal Failure Finding Inspection interval for the extended life period. The main purpose of this paper is to develop analytical and graphical methodologies to identify the optimal FFI interval for extension of the discard life of aircraft components. The paper considers repairable components which are periodically tested. The methodology assumes that the inspection and repair actions lead to as-bad-as-old (ABAO) reliability characteristics.The graphical approach proposed in this paper considers inspection and repair times, as well as the costs associated with accidents, inspection, and repair, and it takes into account the opportunity losses due to the maintenance downtime. The analytical approach for calculating the unavailability of the hidden function is based on the Mean Fractional Dead Time (MFDT).
|
|
| 6. |
- Ahmadzadeh, Farzaneh, et al.
(author)
-
Mean Residual Life Estimation Considering Operating Environment
- 2012
-
Conference paper (peer-reviewed)abstract
- The cost of maintenance of mechanized and automated mining systems is too high necessitating efforts to enhance the effectiveness of maintenance systems and organization. For effective maintenance planning, it is important to have a good understanding of the reliability and availability characteristics of the systems. This is essential for determining the Mean Residual Life (MRL) of systems so that maintenance tasks could be planned effectively. In this paper we used the statistical approach to estimate MRL. A Weibull proportional hazard model (PHM) with time-independent covariates was considered for modelling of the hazard function so that operating environment could be integrated in the reliability analysis. Methods are presented for calculating the conditional reliability function and computing the MRL as a function of the current conditions to guarantee the desired output. The model is verified and validated using data from the Hydraulic system of an LHD fleet from a Swedish mine. The results obtained from the analysis is useful to estimate the remaining useful life of such system which can be subsequently used for effective maintenance planning and help controlling unplanned stoppages of highly mechanized and automated systems.
|
|
| 7. |
- Aminu Sanda, Mohammed, et al.
(author)
-
Lean instrumentation framework for sensor pruning and optimization in condition monitoring
- 2011
-
In: The Eighth International Conference on Condition Monitoring and Machinery Failure Prevention Technologies. - Longborough, Glos : Coxmoor Publishing Co.. - 9781618390141 ; , s. 202-215
-
Conference paper (peer-reviewed)abstract
- This paper discusses a lean instrumentation framework for guiding the introduction of the lean concept in condition monitoring in order to enhance the organizational capability (i.e. human, technical and management trichotomy) and reduce the complexity in the maintenance management systems of industrial companies. Additionally, decision-making, based on severity diagnosis and prognosis in condition monitoring, is a complex maintenance function which is based on large data-set of sensors measurements. Yet, the entirety of such decision-making is not dependent on only the sensors measurements, but also on other important indices, such as the human factors, organizational aspects and knowledge management. This is because, the ability to identify significant features from large amount of measured data is a major challenge for automated defect diagnosis, a situation that necessitate the need to identify signal transformations and features in new domains. The need for the lean instrumentation framework is justified by the desire to have a modern condition monitoring system with the capability of pruning to the optimal level the number of sensors required for efficient and effective serviceability of the maintenance process. It is concluded that there are methodologies that can be developed to enable more efficient condition monitoring systems, with benefits for many processes along the value chain.
|
|
| 8. |
- Arasteh khouy, Iman, et al.
(author)
-
Geometrical degradation of switches and crossings on a Swedish heavy haul railroad : a case study
- 2013
-
In: Proceedings of 10th International Heavy Haul Association Conference. - New Delhi, India. - 9788192651903 ; , s. 26-32
-
Conference paper (peer-reviewed)abstract
- Switches and crossings (S&Cs) are one of the most critical components of railway track systems in terms of safety, operation and maintenance. Each year, a considerable part of the maintenance budget is spent on inspection, maintenance and renewal of S&Cs. However, applying a cost-effective maintenance strategy helps to achieve the best performance at the lowest possible cost. In Sweden, the geometry of S&Cs is inspected at pre-defined time intervals by the STRIX track measurement car. In this paper, time series for the measured longitudinal level of S&Cs on the Iron Ore Line (Malmbanan) in northern Sweden have been used. Two parameters have been defined in this study, namely the absolute residual area (ARa) and the maximum settlement (Smax), to analyse the geometrical degradation of switches and crossings due to dynamic forces generated from train traffic. The paper also evaluates the growth rate of the longitudinal level degradation as a function of million gross tonnes (MGT). The results facilitate correct decision making in the maintenance process through understanding the degradation rate and defining the optimal maintenance thresholds for the planning process. In the long run this will lead to a cost-effective maintenance strategy with optimized inspection and maintenance intervals.
|
|
| 9. |
- Asplund, Matthias, et al.
(author)
-
Inspection of railway turnouts using camera
- 2013
-
Conference paper (peer-reviewed)abstract
- The railway turnout is an essential component in a railway system, used to divert traffic along different tracks. A turnout includes a number of different parts, including the switch blade, frog, point machine, switch roller, soleplate, check rail, wing rail, drive rods, control rods and other bars. These parts must be kept in good condition, meeting functional and safety requirements. Failing to comply will result in a reduction of the network’s capacity with economic consequences. Not honouring the safety limits could result in severe accidents, including derailment, causing human casualties. By performing the right type of inspection and/or maintenance at the right time, these unwanted events can be reduced. To determine if and when a maintenance action should be performed, the condition of the turnout must be established, usually by manual inspections or with measurement vehicles. The drawback is the discrete nature of these inspection events. Failure modes with development times shorter than the inspection interval could result in a malfunction of the unit. An on-line measurement system would be able to deal with these failure events and initiate correct maintenance actions at an earlier stage. With an on-line system, remotely located turnouts could be inspected without on-site personnel. Capacity consuming failures of turnouts with a strategic location or with bottleneck characteristics could also be corrected before they affect traffic. This paper describes a feasibility study of a camera based inspection system for turnouts and discusses the effect the method could have on system reliability and capacity.
|
|
| 10. |
- Barabady, Javad, et al.
(author)
-
A method for managing the availability improvement efforts
- 2006
-
In: Engineering Asset Management. - London : Encyclopedia of Global Archaeology/Springer Verlag. - 9781846288142 ; , s. 445-451
-
Conference paper (peer-reviewed)abstract
- Availability is an important characteristic of a repairable system. When the availability of system is low, efforts are needed to improve it. Any improvement in the availability of a system is associated with the requirement of additional effort and cost. Therefore, it is essential to use methods or techniques for availability allocation amongst various components/subsystems of a system with the minimum effort and cost. The concept of importance measures could be used to prioritize the components or subsystems for the availability improvement process. The study shows, it is useful to obtain the availability importance measures value of each component in the system prior to deploying resources towards improving the specific components. With the assistance of importance measures one can identify the components/subsystems that merit additional research and development to improve their availabilities, so that the greatest gain is achieved in the system availability. Each component should be assigned a value and the component with a greater value will have a greater influence on the availability of the system. Generally, the importance of components should be used during the design or evaluation of systems to determine which components or subsystems have the greatest importance for the availability of the system.
|
|
