Analysis on Airframe and Engine Degradation - Research Paper Example

Analysis on Airframe and Engine Degradation Table of Contents Executive Summary 3 0 Introduction 3 1 Project Background 3 1.2 Project Objectives 4 2.0 Project Methodology 5 2.1 The Project Approach Summary 5 2.2 Project Deliverables 6 2.4 Definitions 7 3.0 Literature Review 7 3.1 Airframe and Engine Degradation 7 3.2 Influence of Performance on Fuel Consumption 9 3.3 Available Degradation Prevention Methods 10 3.4 Emerging Degradation Monitoring Methods 11 3.5 Correlation of Aircraft Age and Performance Factor 12 4.0 Criteria Rationale 12 Figure 1: DFFAM and DFFBM Analysis of Old, Medium and New Aircraft 15 6.0 Results 15 6.1 Analysis 15 Figure 3: EGT Trendline for 9M-AQR Aircraft for 2014 17 6.2 Support for Analysis 17 6.0 Conclusion and Recommendations for Future Work 19 Reference 19 Analysis on Airframe and Engine Degradation Executive Summary The purpose of this project was to investigate the cause and effects of airframe and engine degradation. The study combined literature review and empirical Case Study of A320 Air Bus. For the Case Study, systematic sampling of aircraft was conducted to determine deviation flow of fuel due to engine degradation (DFFB) and deviation fuel flow due to apparent airframe deterioration (DFFA) based on regular monitoring of aircraft degradation rate from APM software. The study results show that Mid-range category of aircraft generated the highest airframe degradation (0.195) followed by Old-range Category (0.176) and then New-range Category (-0.026). For the engine degradation, New Category of aircraft produced the highest degradation (0.194), followed by Old-Category (0.106), and then Mid-range Category (-0.062). Since Airbus focus on low-cost strategies, it is recommended that the airline should improve the competency of its technicians as a strategy to enhance the quality of installation monitoring. It is also recommended that the airline establishes uniform schedule for airframe and engine maintenance to eliminate the problem of irregular degradations, and encourage airbrushing livery method to lower the rate of aircraft degradation. 1.0 Introduction 1.1 Project Background Airframe and engine degradation play a very vital role in the airlines industry as it has many affects if not monitored accordingly. The need to investigate and improve the degradation factor has increased as it is able to save abundance of money in terms of lower operating cost. The dramatic increase in jet fuel cost in recent years has had a significant effect on the division of operating costs. In 2003, jet fuel was around US$0.85 per US Gallon. At that time, fuel represented about 28% of the total operating cost for a typical A320 Family operator. By 2006 fuel prices had more than doubled, meaning that fuel now represents around 43% of all operating costs (Getting to grips with A320 Family performance retention and fuel savings, 2008). At the moment every airline will have its own way of monitoring the aircraft performance based on their make. As Air Asia uses entirely airbus fleet of aircraft, the performance monitoring is done using the APM software supplied by airbus itself. Using this we get to see the monthly performance and the degradation for the engine and airframe. This then helps us in planning for the structure and placing for the aircraft in its most useful role. If an aircraft has low performance factor caused by the high degradation this aircraft would be either proposed for makeover or cease of service. As the operating cost is most vital especially for budget airlines like Air Asia, the aircraft has to perform its best at all times. The project may suffer from delay if the timely inspection for the aircraft is not done due to delay in the maintenance department. Another reason for the delay can also be the wireless extraction method not in on time due to downtime by service provider. 1.2 Project Objectives Objective 1 To identify the causes for airframe and engine degradations Objective 2 To elaborate on the effects of these degradations on fuel efficiency Objective 3 To find novel ways for improving prevention of aircraft degradations 2.0 Project Methodology 2.1 The Project Approach Summary The methodology for the study combined literature review and empirical Case Study of A320 Air Bus, an analysis that involved systematic sampling of aircraft to determine deviation flow of fuel due to engine degradation (DFFB) and deviation fuel flow due to apparent airframe deterioration (DFFA). The literature study established current state of knowledge and underpinned research gaps in the following areas: Basic understanding of Airframe and Engine Degradation The influence of the performance to the fuel consumption Prevention methods available Latest development on degradation monitoring methods Correlation of the Age of the aircraft to the Performance Factor For the empirical Case Study analysis of this topic, regular monitoring from the APM software was used as a guideline to check for the aircraft degradations. This was done using the airbus software, Performance Engineer Program. The aircraft produces a cruise report data and can be extracted in two ways, manually or through wireless extraction. The wireless extraction was monitored by another service provider. From the extraction, the report was processed using the PEP software. The values like the specific range degradation (DSR), deviation of fuel flow due to the "apparent" airframe deterioration (DFFA) and the deviation of fuel flow due to the engine deterioration (DFFB) and example of vital values achieved from the report. Once this was done, the trend line was spotted to monitor the degradation. Aircraft weighing is a procedure conducted regularly by Air Asia for their fleet. The researcher assisted the engineers in order to gain knowledge on the weight influence factor to the performance. This allowed determination of correlation between the performance and degradations. Apart from that visual inspections of the aircraft towards the airframe and engine showed the actual deterioration. As certain improper maintenance work done on the aircraft could cost severe fuel damage and lead to the part to degrade at a faster rate. In order to complement cruise performance analyses, and whenever possible, the aircraft should be observed on ground and in flight for any surface misalignment or other aerodynamic discrepancies such as: - door misrigging, missing or damaged door seal sections, control surface misrigging, missing or damaged seal sections on movable surfaces - skin dents and surface roughness. (Getting To Grips With Aircraft Performance Monitoring, 2002). As for future recommendations, this study accounted for the cost of repair to fuel savings achieved on whether it could be justified. At times the cost of repair may exceed the fuel savings achieved but this is not the case all the time. With the aircraft age playing a big factor to it, the concept of repairing a very old aircraft may not be worth the time. 2.2 Project Deliverables The duration for the placement was set to be six (6) months with an option to extend it if necessary. This allowed collection of all materials and data from Air Asia. Weekly updates were provided and a complete report of the study findings and analysis produced by the end of the scheduled timeframe. 2.4 Definitions Airframe Degradation: The degradation which takes places on the aircraft structure itself for example the seals, doors, slats and flaps rigging. Engine Degradation: The degradation which happen on the engine related section for example fuel consumption increase for a given thrust. Performance Factor: negative value indicates aircraft performs better than expected while positive value indicates diminishing performance. APM Program: Software for analysing the degradation of aircrafts using various parameters based on DFFA and DFFB values 3.0 Literature Review 3.1 Airframe and Engine Degradation Aircraft cruise performance declines over time due to the effect of airframe engine degradation. According to Filippone (2012), this reality results from airframe drag deterioration, engine performance deterioration or both. Airframe refers to the mechanical structure of an aircraft including the wings, fuselage, and undercarriage but excluding the propulsion system. According to Kustron (2008), the durability of an airframe depends on its service conditions, design, as well as the durability and damage tolerance (DADT) of the constituent materials. The critical material properties include fatigue resistance, corrosion resistance, fatigue crack growth resistance and toughness. Generally, safety, reliability and durability are the main desirable qualities for aircrafts and other airspace technical objects. However, the main challenge with airframe degradation is the early detection of symptoms of structural degradation before actual damage (Kustron, 2008). This is especially important because airframe degradation has been the cause of various airline flight accidents in past. Most materials used for high speed aircraft structures and engines degrade with time when exposed to extreme temperature (Benson et al., 1998). Icing on aircraft can cause wing stall, icing contamination and degradation. The composite aircraft structure degrades due to impact damage, bonding and de-bonding as well as delamination. On the other hand, the metallic structure degrades due to fatigue crack development, corrosion, impact damage, and stress corrosion cracking. The solution has been emphasis on the use of composite materials to replace the traditional materials as primary structures in order to create optimized airframe with improved materials and advanced designs (Li et al., 2013). Advances in technology and material combinations have led to gradual shift from aluminum to carbon fiber among other strong and lightweight materials, which meet the specific performance requirements for various aircraft components. Many airframe structures consist of 50% advanced composites including very light jet (VLJ), a new generation of jet aircraft with advanced composite materials. For modern aircraft, the design should emphasize on aerodynamic shapes for long-range flight. Furthermore, all structures must withstand hail and lightning strike with structures serviceable from 15 to 20 years with minimum cost (Niu, 1988). Existing literature shows that engine degradation is a major design consideration in aircraft manufacturing because of cost and safety implications. Degradation can result from various sources including the nature of materials, hardware deterioration, EGT margin deterioration, temperature, and ingestion of debris or volcanic air. Further research shows that modern turbine engines have the capacity to sustain fight safety-threatening damage when exposed to volcanic ash (Casadevall, 1994). Overall, engine deterioration occurs due to hardware deterioration, expiry of life-limited parts (LLP), foreign object damage such as ingestion of debris and ash, and water washing or EGT margin erosion. Ingestion of ash and debris can cause degradation associated with classification of hot components, blockage of cooling parts, erosion in compressor rotor path and blading, as well as contamination of air supply and oil system (Dunn et al., 1987). 3.2 Influence of Performance on Fuel Consumption Aircraft fuel efficiency is an important design parameter used by aircraft manufacturers. Reducing fuel consumption is a leading objective due to on-going price uncertainties and environmental concerns (Ryerson et al., 2011). Research shows that the main factors affecting fuel performance in aircraft include engine’s performance, airframe weight and aerodynamic performance. According to the Airbus Flight Operations Support and Services (2008), the main factors affecting fuel consumption include cruise speed, flight level, flight plan accuracy, aircraft performance degradation, and fuel reserves. Airframe weight has remained relatively constant over the years in proportion of aircraft’s Maximum take-off weight (MTOW), partly because aluminum is the main material for fabricating these structures (Hielamn et al., 2007). Nevertheless, fuel consumption per FTK varies considerably with the load factor and the distance travelled. The main idea is that total weight of aircraft is a major determinant of fuel consumption. This means airframe degradation can have a substantial effect on fuel efficiency. Convectional solutions aim at reducing weight of the airframe or weight of the engine, which may also affect aircraft performance parameters due to implications of aerodynamic drag and propulsion efficiency. Innovation in manufacturing techniques and materials can help to reduce engine weight such as reducing the compressor stages or development of blisk components. The problem is that potential gains are small. However, much research has focused mainly on improving engine performance. Two main factors influence engine efficiency: propulsion efficiency, which depends on speed and state of aircraft operation, and cycle efficiency. Designers improve cycle efficiency by increasing compression ratio and elevating the combustor burning temperature (Schumann and Busen, 2000). On the other hand, they improve propulsion efficiency by reducing exhaust speed. 3.3 Available Degradation Prevention Methods A critical analysis of existing literature shows the existence of various methods and techniques for preventing degradation of both airframe and aircraft engine. These include anti-icing systems, which provide protection from icing in icing conditions and de-icing system, which remove ice from contaminated services (Cheng and Tian, 2012). Generally, aircraft icing occurs due to existence of water droplets and ambient temperature lower than 0oC. Icing on the wings degrades flight performance and can cause accidents. Ice detection can involve automatic activation or manual methods where crews activate the protection system after receiving detector signals. Sensors embedded in runways can help in measuring snow and ice depth. The specific techniques include pneumatic boo de-icing, electro-thermal ice protection, and thermal ice protection. Another degradation prevention method is the deployment of technology designed for detection of weather conditions. This is vital because it will allow accurate forecasting of meteorological conditions that may produce icing on airframes and predict lightning strikes. This technology will improve aircraft safety and reduce repairs for airframe damages caused by weather conditions (Cheng and Tian, 2012). Since it is demanding to prevent lightening from striking during flying, the main idea is to prevent damage when it strikes aircraft. This is achieved by careful selection of structures and materials that reduce damage. There are also attempts to prevent contamination of aircraft bearings taking into account careful selection of materials and design features. Plain bearings are used in various aerospace applications in order to connect structures experiencing misaligning and oscillating motions. Solid and liquid contamination is a common problem contributing to bearing system failure and performance limitations. Generally, contamination increases wear rate, airframe degradation and failure. 3.4 Emerging Degradation Monitoring Methods Aging aircraft are generally susceptible to corrosion and fatigue and thus require intensive maintenance and monitoring of degradation. Generally, aircraft engine health monitoring involves two methods: a direct method that entails isolation of engine components in-flight and an inverse method that involves quantification of depredation level post-flight (Simmons, 2014). The isolation method for degradation monitoring suits on-board implementation whereas the degradation quantification approach is a multi-output method for estimating parameters. The convectional nondestructive testing methods may not detect fatigue cracks in multilayered aircraft structure. Consequently, new technology focuses utilization of structural health monitoring technologies (Cheng and Tian, 2012). Ultrasonic testing technology has gained popularity in the recent past as a technique for monitoring degradation in aircraft structures using ultrasonic probes. This method involves measuring changes in sound wave frequencies in order to locate defects and determine their sizes (Cheng and Tian, 2012). Liquid penetrant inspection is another surface-based approach for monitoring degradation using fluorescent dye. For commercial aviation, Eddy current testing is a popular and simple technique for detecting defects using eddy currents. Other techniques include the use of radiographic waves (x rays and gamma rays). 3.5 Correlation of Aircraft Age and Performance Factor According to Herrera and Vasigh (2009), a major concern in the aviation industry is that aircraft are used beyond their designed economic life, which also affects their performance. Preliminary investigations reveal a correlation between aircraft age and performance factor. A previous study by Herrera and Vasigh (2009) revealed a relationship between the number of accidents, their severity and age of aircraft as well as the manufacturer. Generally, safe operation of aircraft is a process that involves interfacing between machines, humans and the environment. Aging machines have declining performance factor and high failure rate. Aging machines may also lead to decreased engine efficiency and high fuel consumption. 4.0 Criteria Rationale The criteria used for this study relies on Airbus degradation values and expectations. Airbus has conducted vast research and produced the predicted trend of the degradation. The company has established that the average typical range deterioration compared with an entry into service level observed by operators with A320 family is as follows: -1.0% after 1 year (±1%) -1.7% after 2 years (±1%) -2.3% after 3 years (±1%) -2.7% after 4 years (±1%) These values represent the typical feet averages as reported by Airbus. From analysed data, individual aircraft variations can go up to ±2% on the specified values (Airbus Flight Operations Support and Services, 2008). 5.0 Experimental Set Up This study involved assessment of the two main factors considered in aircraft degradation: airframe degradation (DFFFA) and engine degradation (DFFB). Two analyses were conducted to find which of the two factors contributed more to the aircraft degradation. The values for DFFA and the values for DFFB were averaged and tabulated for comparison purposes. The airline had a fleet of over 80 aircraft. For the purposes of this analysis, a random sampling method was conducted to select a sample that accurately depicts the entire fleet. Selected aircraft were categorized into three stages according to their age: Old, which represents aircraft purchased in the first 3 years of the Airbus operations, Medium or aircraft purchased within the next 3 years, and New, which is the new category of aircraft. The aircraft selected under the Old category include 9M-AFE and 9M-AFG, Medium category (9M-AHV, 9M-AHU, and 9M-AHW), and New category (9M-AQS, 9M-AQP, and 9M-AQR). This study entailed 5 stages of analysis. Stage 1 involved tabulation of raw data from the PEP software. Three sets of aircraft data for 2014 are enlisted for each section. Stage 2 involved averaging all the raw data into a single set of data for each month. This allowed creation of a single data set for each of the three aircraft. Stage 3 involved dividing the data into three segments for categories Old (1), Medium (2), and New (3). Each category consists of data from January to April, May to August, and September to December, respectively. This categorization helps improve the accuracy of the data for analysis purposes, and in the assumption that there is no significant difference between average of 4 months and 12 months average. In addition, this method allows for the identification of weather conditions throughout the year, which may affect the results. In stage 4, aircraft rate of degradation was identified. Calculation for the rate is in two parts. In the first part, the difference between category 2 and category 1 is calculated. In the second part, the difference between Category 3 and Category 2 is calculated. The results of the first part is labelled as delta January and the second part delta December in order to distinguish between the two. In stage 5, the results for delta January and delta December are averaged for comparisons. All the five stages were applied to the Old, Medium, and New Categories, and plotted in a bar chart for comparison of the factors affecting the aircraft degradation. Figure 1 below shows the graph of DFFAM and DFFBM analysis. Figure 1: DFFAM and DFFBM Analysis of Old, Medium and New Aircraft 6.0 Results Mid-range aircraft recorded the highest degradation rate (0.195), followed by Old-range aircraft (0.176) and then New-range aircraft (-0,026). The trend is different for engine degradation with the New-range aircraft showing the highest degradation (0.194), followed by Old-range (0.106), and then Mid-range (-0.062). 6.1 Analysis The results on degradation rate are not consistent with the trend predicted by Airbus. Various factors could lead to this inconsistency. Further investigations on the possible causes revealed that the maintenance schedules for the aircraft airframe and the engine did not coincide for medium-range aircraft. This caused inconsistent readings for the engine and airframe sections. Another potential cause of inconsistent degradation rate is the quality of repair work conducted by the designated technicians at MRO. In particular, the problem could have arisen due to inconsistent standard of airworthiness during repair as well as poor monitoring. However, airframe can also lead to degradation due to factors such as miss-rigging of the slats, the door, as well as exterior components. This could occur due to heavy maintenance work conducted on Mid-range aircraft airframe, especially during the analysis period. The engine degradation pattern also elicited important insights. First, the engine used for A320 aircraft can vary. Although Airbus uses the CFM 56 engines, this type comes in two models: 56-5B6/3 and the older variant 56-5B6/P. both the New and the Medium range aircraft use the new engine model (56-5B6/3). Data series are retrieved from the Engine Department of Air Asia and tabulated using Engine ground temperature readings. From the graphs, the Mid-range aircraft has greater EGT compared to the New category of aircraft. This is consistent with the initial findings of the DFFAM and DFFBM analysis. The engine operating at high temperature led to high rate of degradation. Figure 1 shows the Exhaust Gas Temperature (EGT) trendline for 9M-AHU (Mid-range) in 2014 Figure 2: Exhaust Gas Temperature (EGT) Trendline for 9M-AHU Aircraft in 2014 Figure 3 illustrates EGT trendline for 9M-AQR (New-range) in 2014 Figure 3: EGT Trendline for 9M-AQR Aircraft for 2014 6.2 Support for Analysis The inconsistency between expected and observed readings on aircraft degradation requires further analysis based on livery work done on them. Livery refers to the graphics displayed by the aircraft on their exterior. There are two methods of livery with important trade-offs: airbrushing, and decal. The airbrushing method suffers limitations of being expensive it has lesser drag. On the other hand, the decal method is cheaper but it creates higher amount of drag. In addition to these trade-offs, livery work involves a number of steps before completion. Prior to their application, two processes are involved- stripping or sanding. The stripping approach clears the paint to the bare metal, which means no additional weight to the aircraft but it takes extra cost and more time to complete. The sanding method involves removing the decal and application of prima. Sanding is cheaper and can be completed in relatively short time but this approach increases aircraft weight. Since Air Asia is a low-cost airline, the priority for this study is to lower the cost of its operations. Therefore, all the aircraft uses the decal method for the livery work because of its lower overall cost implications. Analysis based on livery work shows that midi-range category of aircraft generated the highest number of livery work. This contributed to the high degradation rate observed in this category because of the high drag induced by the body. Figure 4 below shows results of comparison of the livery work done on the selected aircraft. Figure 4: Livery Work 6.0 Conclusion and Recommendations for Future Work This study gives important insights on future work. First, it reveals the need for the airline to increase the quality of installation monitoring. In order to achieve this, it is recommended that the airline improves the competency of its technicians to enable them to work more diligently. Secondly, the study shows the need to ensure consistency in aircraft maintenance work in order to prevent degradation irregularities. It is recommended that airline establishes a uniform schedule for engine and airframe maintenance. Thirdly, although airbrushing method is expensive, the airline should encourage it because decal method creates excessive weight, which increases the aircraft degradation rate. Reference Airbus Flight Operations Support and Services (January 2008). 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