Proactive Maintenance of Aircraft Engines - Research Paper Example

Abstract The review gets aimed at highlighting the key preventive maintenance practices in aircraft engines. Such practises get carried out before the actual damage or fault occurs. Proactive maintained has one primary aim, eliminating the resultant consequences of the actual damage or failure of the aircraft`s engine. Active maintenance also ensures reliability of the engine during operation. The long term and a major advantage of preventive maintenance are the ability to reduce cost that would otherwise have been incurred in both replacing the damaged engine, as well as losses occurring due to downtime. Therefore, proactive maintenance ensures a higher level performance and durability of an aircraft`s engine and thus resulting in significant returns on INVESTMENT in the hardware. Statistically, frequent application of proactive maintenance is considered uneconomical. There is a high cost incurred during the process of carrying out preventive maintenance. For the optimum benefit of the whole system, the maintained practise should be carried out in a proper timing. Such schedules get provided by the manufacturer of the engine. This review document, therefore, aims at putting to light and enabling the reader to understand the importance of proactive maintenance both in literature and mathematically. Maintenance of an aircraft`s engine is majorly carried out by qualified aeronautical technician although some classes of the pilot can carry out some of the simple engine checks before and after every flight. Understanding the proactive maintenance of the entire aircraft is crucial. However, the engine plays over 90% significance for any aviation disasters. Any major aircraft accident gets attributed to engine failure or malfunctions associated with the engine. It is, therefore, necessary for any aviation authority to pay more attention to engine maintenance. The maintenance practise should regularly get done and with the provisions stipulated by the manufacturer. Key Theme Approaches to maintenance practises. Component lifetime and reliability. Preventive and predictive maintenance. Engine lubrication. Maintenance costing and documentation. Maintenance safety Maintenance sustainability and environmental impacts. Introduction Maintenance is a procedural operation an aircraft is subjected to for it to have the capability to fly safely. The span of support begins from the time the aircraft gets purchased and ends when the component under consideration gets considered out of service [1]. Maintenance of several aircraft elements frequently gets scheduled and classified into the following categories. • Proactive Maintenance • Preventive maintenance There are some cases when unprecedented malfunctions present and in such cases, unscheduled maintenance is mandatory. Such cases cause a lot of downtimes in most aviation sectors and results in interruptions to various aspects such as plans, schedules, reputation and monetary loss for the company under consideration. Although preventive maintenance gets purely meant for a positive effect on the aircraft performance, research and practical experiments have shown that such practises result in some risks. Such risks include: • Cases of damage in an adjacent equipment during engine maintenance procedure exist. • The Cost of the engine part undergoing maintenance due to incorrect installation or installation of defective engine component are possible. Such erroneous incidents during proactive maintained renders the whole practise the cause of major engine failure [4]. There are various methodologies and approaches to maintenance practices of an aircraft’s engine. Such methods include: • System analysis. • Zonal Analysis. • Structural analysis. The result of each of the approach indicated above has a contribution to the outcome and reliability measure of the maintenance procedure. Thus, the methods form an integrated preventive maintenance package. The figure 1 below shows a proactive maintenance schedule. Fig 1. Proactive maintenance schedule Typically, each of the approaches addresses a particular aspect of maintenance and should, therefore, be but into consideration. 1. System Analysis System analysis puts more focus on functional systems within the equipment than other analysis methods. Such systems include control, braking, pneumatic, combustion and other eminent systems within an aircraft`s engine. In such a case, the analysis comprises of stages the First stage being FMEA (Functional Failure Modes and Effect Analysis. Importance of system analysis System analysis helps in identification of potential failure modes. Such functionality is purely predictive and highly dependent on signs within the engine. The analysis also helps in identification of the most appropriate proactive maintenance for the failures identified. The frequency of performing such maintenance practices also gets determined from system analysis. 2. Structural analysis The structural analysis pays more attention to the fundamental aspects of the aircraft's engine more than any other part. The structural elements, in this case, refer to the entire design of the engine as well as other components that work in correlation with the engine. Importance of system analysis Structural analysis helps in identification of maintenance tasks that would help in addressing structural failure. Structural failure in most cases have adverse effects and may occur in the form of fatigues, environmental deterioration or in some cases may occur as accidental damage. 3. Zonal analysis Zonal analysis helps in the derivation of requirements for zonal inspections. In most cases, zonal inspections are taken as a general visual inspection practise. Importance of zonal analysis The zonal analysis identifies the kind of defects that are not eminent and may not get detected by either structural or system analysis. Thus, zonal analysis plays the wider role maintaining an aircraft’s engine against some of the defects that are random in nature and hardly predictable. In his research, Knezevic discovered and reported that there was a high possibility of facilitating proactive maintenance practise by putting into consideration some tactics during aircraft design. In some cases, sophisticated aircrafts are flown with an inherent substitute engine system within the will replace a damaged system during operation [7]. Alper in his study also publishes some literature on the importance and necessity of laying down maintenance schedules in accordance with the location`s conditions. As an illustration to his suggestion, he states that it would be an essential need to perform a reliability analysis on two parts of an F-16 fighter jet engines in Turkey. The said drivers in the fighter jets have been reported to experience failure often [8]. Wilmet and Usrey in their literature portrayed the possibility of the existence of a higher improvement in the existing maintenance procedures. The development as suggested would be realized by employing the use of reliability-based maintained for DC power supplies. They further observed that reliability-based proactive maintenance have a high efficiency in the prevention of some of the critical failures or when the existing preventive maintenance practises are not entirely efficient [9]. Kipersztok, however, described an approach of performing engine diagnostics for an aircraft at the airport`s gate. The method gets based on Bayesian analogy on the maintenance practice support enhanced through diagnostics at the airports gate. The approach integrates both engineering and mechanics knowledge together with statistical reliability data. However, a higher degree of integration of diverse knowledge in the airplane maintenance practise leads to an ambiguous diagnosis. In such a case, Bayesian network helps get rid of ambiguity by the use of a mechanism that ensures consists update that helps get rid of any ambiguity between any possible sources of failure [10]. Several methods were suggested by Wu et. as to reduce significantly on operating costs for commercial aircrafts. However, the primary way to achieve the goal is by proper design and effective diagnosis of possible malfunctions. The design of Boeing 777 gets based on the principle stated above and has very low operating costs than similar aircrafts. The study carried out by Wiksten and Johanson revealed the importance of effective decision-making regarding the proactive maintenance of an aircraft. The decision-making process gets based on maintenance data available. The two researchers proved the approach by analysing maintenance and operation data for an aircraft to determine reliability, cost and its usability [12]. An innovative safety algorithm got proposed by Leung et.al that simplifies reliability analysis and makes quick and accurate calculations. The method has proved that in improved systems, the method has capabilities of predicting downtimes and enhanced precautionary actions takes [13]. Hinton and Miah made various efforts in the field of maintenance practices for an aircraft`s engine. They developed reliability based program that would check an engine against corrosion. The program`s primary function is to identify the existence of corrosion anywhere within the engine and also gives desired preventive maintenance procedures to counteract the same [14]. Marusic et.al made more studies focusing on reliability-related programs based on smaller aircrafts. The program suggests that in cases where there exists insufficient data to enable adequate statistical analysis increasing the fleet virtually is important. Increase the size of the fleet reduces the size of distribution thus avoiding wrong decisions. The calculations should, therefore, get based on the new size of fleet determined virtually and decisions on preventive maintenance should be made based on the outcomes [15]. Jula et.al carried out a case study and carried out practical research on aircraft`s electric power system analysis. The study was carried out by use of Boolean logical structure to define a representative fault tree. The fault tree represents all combination of factors that are likely to result in failure in the aircraft`s electric system. The program aims at enhancing the fault tolerance of the system [16]. A subject-based maintenance practise was proposed by Guzzi et.al by use productive system model. The policy was condition based gets optimized by adequate adjustment of support thresholds. The changes get aimed at reaching the lowest level global system cost. All maintenance and production cost get taken into consideration by performing a simulation of the aspects. A parametric study in such case helps in determination of effects of critical elements of the achievement of an aircraft`s preventive maintenance practise [17]. Viorel presented two modern maintenance training. The author suggested that maintenance, as well as Focus on the final productivity of the support exercise, are necessary for analysing the characteristics of the method [18]. A study by Gherghinescu together with Popescu revealed that by application of complete functional proactive maintenance, the following results are achievable. • A drastic reduction of more than ten times the amount of cost invested. • A reduction of between 25% and 30% of the reasonable value used in maintenance for a well monitored engine. • A drastic depreciation of between 35% and 45% of the stationary time. For any efficient and effective proactive maintenance practise, the procedure should be economic based. However, for better results, two key parameters require practical elimination [20]. • Mean time between failures. • Mean time to repair The two aspects mentioned above can get determined and analysed mathematically which will be covered later in the review. The mathematical approach to the two issues aims at numerically revealing the importance of proactive maintenance for an aircraft`s engine. The mean time to failure (MTTF) is considered a reliability criteria. The numerical values obtained both when dynamic maintained gets applied and when the practise do not get used gets compared to the Mean time to failure set point value for a reliable preventive maintenance method. For any aircraft, engine maintenance is diverse. However, some of the approaches used in carrying out the task of preventive maintained of the engine are more efficient than others. The reliability of the methods used depends on the outcomes of direct applications of the various methods. All the approaches suggested by various researchers are all based on case studies and are subject to defects. No. Themes 1 Fundamental approaches to maintenance, the planning and scheduling function 2 Preventive and predictive maintenance 3 Component life time and reliability 4 Lubrication 5 Maintenance costing, documentation 6 The maintenance organisation (department), report writing 7 Maintenance safety 8 Sustainable maintenance and the environment Table 1. Weekly coverage in this unit. Critical Reflection and Discussion Engine reliability, as suggested by many authors, can be accessed based on Meant Time to Failure (MTTF) and Mean Time before Failure (MTBF) criteria. For those components in the aircraft`s engine regarded as nor repairable, such as the electronic system, Mean Time To Failure gets used. However, for parts that can get repaired, Meat Time before Repair is used [21]. Mean Time before Failure is typically given by the expression below: Where: f(t) is the probability density function. R(t) represents the defined reliability. Probability densifies defined by the expression shown below. In this case f (t) is a function representing the cumulative distribution. Under normal circumstances: F (t) + R (t) = 1 when analysing components regarded to as non-repairable. Engine Failure rate or hazard function Hazard function is represented by the equation below. The expression has been proved to give an instantaneous rate of failure or hazard probability. For repairable components, failure density is given by the equation shown below. The frequency,a repairable component undergoes proactive maintainance is given by: Reliability enhancement In order to enhance the level of reliability in an aircraft`s engine, several maintenance operation has to be put in place. Most of these operations incur extra cost to the existing standard budget. Such services include: • Creating engine component backups in order to cut down maintenance time. • Creating more measurement methods and increasing the frequency of engine preventive maintenance practices. Financial Aproach to preventive maintainance A detailed financial analysis of the preventive maintenance method employed in an aircraft`s engine enables a company to determine the cost of reliability. The cost of reliability gradually reduces after attaining a particular value. Fig. two below shows the relationship between cost and reliability in any system [18]. Fig 2: Graphical relationship between cost and reliability. Preventive maintenance in terms of reliability As an illustration of the importance of proactive maintenance in an aircraft, a simple analogy is presented as shown. The analogy compares the reliability with the time when there is an active conservation practice in a system and when there is no existing proactive maintenance in place. Fig 3: Reliability variation when there is no proactive maintenance The graph shows that the reliability goes to zero (0) in a period of five years if there is no proactive maintenance policy in the aircraft`s system especially the engine system. For safety and optimum productivity purposes, zero value of reliability is completely undesirable in any aviation sector. If we apply equation (3) and using t = 5 years, the hazard function tends towards infinity in an asymptomatic function. However, when preventive maintenance gets administered on an engine system for any aircraft on an annual basis, the reliability will never fall below 0.8 as shown. According to this study, if we consider the fact that proactive maintenance will get made at intervals of one year, then we can show the relationship between preventive maintenance and reliability. The same approach will also show the relationship between the ma9intanance practice and the Mean Time to Failure. The appropriate calculation is obtained by using equation (11): In this case, R (1) =0.8 Fig 4: Reliability variation when there is a constant preventive maintenance. However, when there is an annual application of preventive maintenance in a system, hazard function never tend towards infinity. Rather, the hazard function lies between 0.2 and 0.25. The relationship and range can be represented graphically by the graph shown. Fig 5: Variation of hazard function with annual application of proactive maintenance. Preventive maintained for an aircraft engine involves procedures and operations such as inspection of the engine and its components, overhaul as well as repair. Preservation and replacement of worn out parts are also one of the major process employed as a preventive maintenance [9]. There are strict and well-stipulated procedures and regulations that must be adhered to while performing preventive maintained to any part of the engine. 400 series of FAR govern the rules. Part 91 of this policy document stipulates the standard regulations in performing proactive maintenance for an engine`s aircraft [14]. However, the regulation vary for commercial aircraft and those that are individually owned. In a nutshell, individually owned plane have a relatively flexible preventive maintenance policy. The policy states that the process is entirely dependent on the owner of the aircraft [10]. The standards for almost all commercial aircrafts are similar and relatively strict. The level of strictness subjected to the proactive maintenance of commercial planes is largely because of the nature of their functionalities. Commercial planes usually deliver people and goods on the public side of the economy. A slight error in aircrafts performance that may result in a crash or delays has serious implications for both the company and the costumes. On the extreme, accidents such has plane crash especially the passenger aircrafts results in terminal catastrophes with eminence in a complete loss of lives. The maintenance practise in such commercial planes, therefore, is performed under strict regulations. With the recent advancements in technology, engine failures in aircrafts are becoming rare. The diagnosis tools both hardware and software have been advanced such that faults can be predicted within a short period and with an outstanding accuracy. Summary The study majorly addresses the importance of proactive maintenance of an aircraft’s engine I terms of reliability. The research has tried to use practical applications to validate the argued facts by practical examples of an aviation sector. Preventive maintenance have a cost implication and determination of an optimum frequency of the maintenance practise is important. Too frequenting proactive maintained in an engine has a negative cut implication since the exercise is costly [11]. Since preventive maintenance should is expensive, unnecessary parts may be left out during the process as a means of balancing the cost burden. Omitting of some parts may reduce the reliability of the system under consideration but, in the long run, the cost implication it may incur later may be very high. The conclusion made in the description above are only possible when a single part of an aircraft’s system gets considered. However, the complexity of considering similar calculation for the entire plane amounts to very complicated calculations [17]. Downtime, as seen above, has a negative impact on the economic growth of any aviation sector. Preventive maintained gets directly related to downtimes experienced. However, downtimes due to engine failure are the most drastic causes of downtimes. More attention to aircraft`s engine preventive maintenance should get considered. The reliability-based test described above got simplified by the existence of software’s. There are software’s primary market that analyse the safety and monitor cost of every proactive maintenance in an aircraft. Although such software has a high capital cost, their contribution to the safety of entire aircraft is unutterable. References REFERENCES [1] M. Kayrak, “Aircraft Maintenance and Repair Lecture Notes”, Anadolu University, Civil Aviation School, Eskisehir, unpublished. [2] F. Taskin, “Optimization of Buffer Inventory for Regular Preventive Maintenance Using Fuzzy Logic”, M.S. thesis, Sakarya University, 2006. [3] J. Endrenyi, Reliability Modeling in Electric Power Systems, John Wiley and Sons, 1980. [4] W. C. Worsham, Is Preventive Maintenance Necessary?, 2011. http://www.maintenanceworld.com/Articles/worshamw/ispreventive.htm l [5] Reliability and Maintainability Engineering Program Approach, 2011. http://www.mtain.com/prog/rmprog.htm [6] Reliability Centred Maintenance – RCM, 2011. http://www.fleetech.com/?/1739/1303/2272 [7] J. Knezevic, “Chief mechanic: the new approach to aircraft maintenance by Boeing”, Journal of Quality in Maintenance Engineering, Vol. 5, No. 4, pp. 314-324, MCB University Press, 1999. [8] M. Alper, “Devoloping Method Aircraft Maintenance Planning Reliability Analysis”, Ph.D. dissertation, Anadolu University, 2000. [9] R. G. Wilmeth, M. W. Usrey, “Reliability-centered maintenance: A case study”, Engineering Management Journal, 2000. [10] O. Kipersztok, “Diagnosis Decision Support for Airplane Maintenance”, In Advances in Scientific Computing, Computational Intelligence and Applications, Mathematics and Computers in Science and Engineering, 2001. [11] H. Wu, Y. Liu, Y. Ding, J. Liu, “Methods To Reduce Direct Maintenance Costs For Commercial Aircraft”, Aircraft Engineering and Aerospace Technology, Volume 76, Number 1, pp. 15–18, 2004. [12] J. Wiksten, M. Johansson, “Maintenance and Reliability with Focus on Aircraft Maintenance and Spares Provisioning”, Bachelor Thesis, Lulea University, 2006. [13] T. Leung, T. Carroll, M. Hung, A. Tsang, W. Chung, “The Carroll-Hung Method For Component Reliability Mapping In Aircraft Maintenance”, Quality and Reliability Engineering International, Volume 23, Issue 1, pp. 137–154, 2007. [14] S. Miah, B. Hinton, “A Corrosion Related Reliability Centred Maintenance Pilot Program For The Royal Australian Air Force C-130 J-30 Hercules Aircraft”, Tri-Service Corrosion Conference, 2007. [15] Z. Marusic, B. Galovic, O. Pita, “Optimizing Maintenance Reliability Program For Small Fleets”, Transport, Vol. 22, No 3, pp. 174–177, 2007. [16] N. Jula, C. Cepisca, M. Covrig, C. Racuciu, T. Ursu, “Boolean Applications in Aircraft Electric Power Systems Reliability Analysis”, 2nd European Computing Conference, Malta, 2008. [17] G. Guizzi, M. Gallo, P. Zoppoli, Condition Based “Maintenance: simulation and optimization”, 8th WSEAS International Conference on System Science and Simulation in Engineering, 2009. [18] P. Viorel, “Modern Management Concepts of Maintenance Activities”, Recent Researches in Manufacturing Engineering, pp. 138-140, 2011. [19] S. Gherghinescu, G. Popescu, “In-situ predictive maintenance by vibration analysis for Cryogenic Pilot Plant for Tritium and Deuterium Separation”, Recent Advances in Environment, Energy Systems and Naval Science, 2011. [20] E. Briano, C. Caballini, P. Giribone, R. Revetria, “Design of Experiment and Montecarlo Simulation as Support for Gas Turbine Power Plant Availability Estimation”, Proceedings of the 12th WSEAS International Conference on Automatic Control, Modeling & Simulation, 2010. [21] R. Billington, R. N. Allan, Reliability Evaluation of Engineering Systems, Plenum Press, 1992. [22] C. E. Ebeling, An Introduction to Reliability and Maintability Engineering, McGraw-Hill, USA, 1997. [23] Statistics Tutorial: Discrete and Continuous Probability Distributions, 2011. http://stattrek.com/lesson2/discretecontinuous.aspx Acknowledgements I would like to acknowledge the unending contribution of my group members in accomplishing some various parts of this re[ort. Their brainstorming ability and level of thinking are a direct contribution to all the efforts depicted in the review. Great acknowledgment also goes to our Supervisor for his/her resourceful information that enabled us finish the report.(KINDLY fill this section accordingly with names or salutation from various personel). Read More