IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge21 .+ge21 The Operation Management Model of Aircraft Maintenance, Repair and Overhaul (MRO) Business Hsien-Ming CHANG 1, Abdullah KORA 2 Aerospace MBA, Toulouse Business School E-mail : hm.chang@tbs-education.org1 a.kora@tbs-education.org2 Abstract:Theaircraftmaintenance,repairandoverhaul (MRO)isimportanttotheairlineoperation.TheCcheckand DcheckneedthelongerleadtimeandhighercostthanA checkandBcheck.Itisthegood opportunityforprofessional MROCompanytogetthebusinessfromairlines.Thisstudy proposetheOperationManagementModel,whichintroduce theconceptofleanproductionandsustainabledevelopment intothemaintenanceprocessandmanagementprocessfor MROCompany.ThustheMROCompanycanincreasethe performance and competence in the competitive market.Ke!ords:aircraft,MRO(Maintenance,Repairand Overhaul),OperationManagementModel,LeanProduction, Sustainable Development. "# $ntroduction Themaintenance,repairandoverhaul(MRO)businessmodel for airlines is a combination of an airlines technical capability andlogisticsconfiguration,includingthedegreeofsupply chainverticalintegrationandoutsourcingpractices(Hamad Al-kaabietal.2007).TheimportanceofMROcanbejudged bythefactthatitconstitutestypically10-15percentofan airlinesoperatingcost(Seristo,1995).BaseontheAirline OperationalCostsBreakdownfromIATA(ChrisMARKOU, 2012),maintenancecostis12%ofairlineoperationalcost, refer to Figure 1. Figure 1 IATA Airline Operational Costs Breakdown (Chris MARKOU, 2012) EstablishinganairlineMROprocessisthereforeassociated withhighinvestmentincapabilities.Formanyairlines, especiallynewentrants,thisisnotpossibleduetothelarge capital investment required. Hence outsourcing is considered as an alternative to vertical integration (Heikkila and Cordon, 2002).Manyairlinesstartedtotakeadvantageby outsourcing non-core intensive labour activities and focusing on fewer value-added MRO activities (Rosenberg, 2004).Baseontheaboveanalysis,themaintenance,repairand overhaul(MRO)businessofaerospaceindustryisamajor portionofoperatingcost.Thisstudyproposetheconceptof HighEfficientMROOperationManagementModelfor aircraft industry. %# Operation Management Model TheproceduresofaircraftMROCompanyincludethe physical flow and information flow. The physical flow is the aircraftmaintenanceprocess,whicharecomposedof professionalmethodology,material,machine,manpower, andenvironment.Theinformationflowisthecompany management process, which are based on plan, do check, and action cycle. ThisstudyconstructandproposetheHighEfficientMRO OperationModel,showsasFigure2.Wedescribethe customerdemandinsection3,explainthemaintenance processinsection4,designthemanagementprocessin section5,andsummarythecustomersatisfactioninsection 6. CategoriesMethodologyMachine Material EnvironmentManpower GoalMaintenance Process (4M+1E)EngineeringEvaluationFacility & LayoutHuman ResourceManagement Process (P-D-C-A)Demand IntegrationMaterial LogisticsManagement SystemCustomer Satisfication-Quality-Delivery-Cost-FlexibilityCustomer Demand-Capability-Capacity Figure 2 High Efficient MRO Operation Model IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge22 .+ge22 'ustomer (emand TheimportanceofMROcanbejudgedbythefactthatit constitutestypically10-15percentofanairlinesoperating cost (Seristo, 1995). TheMROCompanyshouldfocusonthecurrentmarketand forecast the future demand. Setup the long term, medium term, andshorttermdevelopmentplan.Reviewandadjustthe capacityandcapabilityperiodicallytofulfilthecustomers demand and sustainable development. &)"# 'apabilit The full certification of the aircraft includethe type certificate fordesign,productioncertificateformanufacturingprocess, and airworthiness certificate for aircraft.Everycountryorairlinehashisownregulationand requirement.TheglobalMROCompanyneedtobeaudited and get certified by various airworthiness authorities. Also, the MRO Company have to create and integrate his own standards to meet the requirements of different customers. ThequalitysystemofMROCompanyshouldbecertifiedby aviationadministrator,suchasFAAandEASA.Manpower, facilitiesandequipmentalsoneedtobequalifiedtoproceed the relative maintenance operations. &)%# 'apacit As system complexity increases, greater technical maintenance expertiseisneededalongwithsophisticatedtestequipment (Esker et al., 1990).The maintenance resources include: 1.Hangarspace:thehangarspacecanproceedtheaircraft maintenance and turnover. 2.Qualifiedequipment:includetestingandmeasuring equipment(e.g.NDI,coordinatemeasurement machineetc.) 3.Qualifiedmanpower:includeengineeringevaluation manpower,inspectionandtesting,structurerepair,part fabrication,painting,harness,avionicstechniciansetc.Maintenancemanpowermustbetrained,expertise,and licensed in specific equipment/operation for maintenance. The MRO Company should analysis the workload and capacity ofthemaintenancevaluestream,andtrace/monitorthe constraintandeliminatebottleneck.Thenconstructthe balanced*# Maintenance +rocess Themainproceduresarereviewflighthistory,determine maintenanceitems,receivingprocess,disassembly,inspection andtesting,assembly,functionaltest,flighttest,anddelivery. TheGeneralMaintenanceProcessofAircraftshowasFigure 3. ReviewFlighthistoryDetermineMaintenanceitemsReceivingProcessDisassemblyFightTestFunctionalTestAssemblyInspectionand testing Figure 3 General Maintenance Process of Aircraft flow shop. 1.Reviewflighthistory:Reviewthelogbookofaircraft andpreviousmaintenancerecords,evaluatethecurrent status of specific aircraft. 2.Determine maintenance items: Base on the maintenance requirementofaircraftmanufacturerandengineering evaluation of currentstatus, determine themaintenance items. 3.Receivingprocess:Receivetheaircraftfromcustomer, cleantheaircraft,andthenloadonassemblyjigsand setup tooling.4.Disassembly:Removethefasteneranddoor/skinof relative maintenance area.5.Inspectionandtesting:ApplytheNDIequipmentand processestoinspectandtestthekeypartsofaero-structures/components.Utilizethetestingequipmentto verifythefunctionofhydraulic,electrical,wiring, avionicssystemsetc.Iffindthedefectivepartsor malfunction,itshouldrepair/fabricatenew parts/moduleforreplacementbasedontheengineering evaluation and disposition.6.Assembly:Replaceandassemblytherelativepartsand components in specific aircraft. 7.Functionaltest:Implementtherelativefunctionaltest after assembly. 8.Flight test: Proceed the flighttest to ensure achieve the original performance requirement. *)"# ,ngineering ,valuation TheEngineeringdepartmentbaseonthemaintenance requirementofaircraftmanufacturer(Airbus/Boeingetc.), flightrecords(flighthours,flightcycle,andcalendartime) and previous maintenance records (A/B/C/D check), proceed theengineeringevaluationofcurrentstatus,thendetermine themaintenanceitemsanddevelopthemaintenance program. Theengineeralsohastoevaluatetheprosandconsofthe newaircraftaddtothefleetofairline.Developthenew ground equipment to support the operations of all fleet.DuetotheairlineandMROCompanyhavetoconsiderthe aircraftavailability,reliability,maintenanceduration,and maintenancecost.Theengineershouldimprovethe competencetodevelopcustomizedmaintenanceprogramto meet the requirement of airlines. IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge23 .+ge23 *)%# -acilit and .aout TheMassachusettsInstituteofTechnologyLeanAerospace Initiative (MIT, 2005) found the following benchmark: 1.Labour hours: 10-71 percent improvement; 2.Costs: 11-50 percent improvement; 3.Productivity: 27-100 percent improvement; 4.Cycle time: 20-97 percent improvement; 5.Factory floor space: 25-81 percent improvement; 6.Traveldistances(peopleorproduct):42-95percent improvement; 7.Inventory or work in progress: 31-98 percent improvement; 8.Scrap,rework,defectsorinspection:20-80percent improvement; 9.Set up time: 17-85 percent improvement; and 10. Lead time: 16-50 percent improvement. Facilityshouldapplysustainabledevelopmentconceptto reducetheenergyconsumption,showasFigure4.The following options can be taken: 1.Utilizethesunlightthroughthehangardesigntoincrease theilluminationandbrightnessofworkspaceanddecrease electrical energy consumption. 2.Collect the clean energy (solar energy) by using solar panel to support lightening system.3.Developnewtestmethodology/equipmenttoreduce fuel/energy consumption. Figure 4 Sustainable Development Concept for MRO Hangar

Layout should apply Lean Production Concept to reduce the maintenance lead time, shows Figure 5 and describes as followings: 1.Themanagementandprofessionalfunctionalgroupsare located in the center of the MRO hanger, they canmonitor themaintenanceprogressandprovidethetechnical supports to both side right away. 2.The receiving warehouse is centralize and the movement of materialflowsareradicaltowardtoeachaircraftduring maintenance. 3.Applytheconceptofpoint-of-usetocreatethefeederline to support assembly line. According to daily requirement of detailproductionscheduleofmaintenance,pickupthe requirement detail part in the handcart and delivery to shop floorjust-in-time.Alsocollecttheunserviceablepartfrom eachaircraftandstorageinfixedstorageareafor disposition.4.The removable equipment dis-assembly from aircraft can temporally storage in both side of hangar, where near the maintenance aircraft. Figure 5 Lean Production Concept for MRO Hangar layout Accordingtothefuturedemandandmarketforecasting,the MROhangaralsokeepthepossibilityforfutureexpansion, show as Figure 6. The advantages of the expansion layout are: 1.Centralizedwarehouseandradicaldistributetoeach aircraft base on daily maintenance plan and requirement. 2.Centralized the management and functional resources. 3.On-site support the progress of each aircraft. Figure 6 Reserve Expansion Opportunity for future development TheDetailLayoutforMROHangarrefertoFigure7(the firstfloor)andFigure8(thesecondfloor).Thegroundrule describe as follows: 1.Theonsitesupportteam,composedbyfunctional /technical groups, which related to maintenance operation should located near to the aircraft. 2.Theprofessionalworkshop,includesavionics,electrical, hydraulic,mechanicaletc.,shouldconnectwiththe relative warehouse and aircraft. 3.Theshopmanagerandmanagementteam/supporting departments,includesengineering,productionplanning, procurement,marketing,financialdepartmentetc., IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge2" .+ge2" shouldgettogethertoreducethecommunicationinterface and increase management effectiveness. 4.Arrangecustomersofficeforbettercommunicationand negotiation. Figure 7 Detail Layout for MRO Hangar (The first floor) Figure 8 Detail Layout for MRO Hangar (The second floor) ApplytheinformationtechnologytoconstructMaintenance ManagementSystem,showasFigure9(overallprogress)and Figure 10(specific aircraft). Figure 9 shows the overall progress of aircraft inside the MRO Hangar. From thescreen, theinformation of customer, aircraft serialnumber,plandeliverydateandestimatecompletedate. Thecolorcodeshowthemaintenanceprogressisonschedule (green color) or behind schedule (red color). Figure 9 Maintenance Management System-Overall Progress Figure10showstheprogressofspecificaircraftinsidethe MRO Hangar. From the screen, the information of customer, aircraftserialnumber,planprogressandcurrentprogress, detailinformationrelatedtoworkinghour,shortages,and quality.Thecolorcodeshowthecurrentmaintenance progress is normal (black color) or abnormal (red color). Figure 10 Maintenance Management System-Specific Aircraft The following actions can be taken in each functional workshop: 1.Construct the Shop Floor Control System (SFCS) to monitor the maintenance activities. Base on the detail production schedule of maintenance, setup the online LCD (liquid crystal display) to demonstrate the visibility and monitor the relation between plan schedules versus current progress. Highlight the current critical issues (such as quality defect of detail parts, shortagesetc.) and potential risk in the future. Also mention the responsible person/organization of relative issues, need date, and complete. 2.Theshopfloorcontrolsystemcollectthelaborworking hourdailyandconverttotheperformancemeasurement reporttosupportshopmanagertakeactionsindaily operations. IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge25 .+ge25 *) /uman Resources ThecriticalhumanresourcesofMROCompanyarethe experienced engineer and qualified technicians, the major roles of engineer and technician are describe as Figure 11: 1.Engineer:Theengineeringnotonlyexperiencethedesign concept, regulation, specification to maintain the reliability ofaircraft,butalsoawarethenewlydevelopment technology and economic sense to make appropriate design (tolerance,material,geometry,manufacturing methodologyetc.)anddisposition.Engineeralsoprovide technicalsupportfortroubleshootingandmaintenance plan development.2.Technician:Thequalifiedtechnicianscoverseveral categories,describeasTable1.Themanpowerhadbetter to be trained as multi-skill workforce to keep the agility and flexibility in the shop floor. Figure 11 Major Roles of Engineer and Technician Table 1 The Qualified Technicians in MRO Shop TypeCatgories MechanicStructure repair, Painting, Assembly ElectricAvionics, Harness, Wiring TestingNDI, functional Test 0# Management +rocess Themanagers'mainproblemistofindagoodmatchbetween workloadandworkforce.Theelementsthatplayaroleinthis matcharetimetables,maintenancenorms,andcontractsfor theworkload,shifts,andteamsoftheworkforce.Thequality of the match in a certain planning period (day, week, or month) isexpressedintermsoftheservicelevelandtheutilization rate. (MATTHIJS C. ThDlJKSTRA et al., 1994) This study utilized the P-D-C-A (Plan-Do-Check-Action) cycle andproposetheManagementProcessofMROCompany, shows as Figure 12. It includes the major functions of demand integration and material logistics, which describe in section 5.1 and 5.2 respectively. 0)"# (emand $ntegration The demand integration include the following steps: 1.Deliveryschedule:Receivetheordersfromdifferent customerswithquantity,deliverydate,modeltype,and conditions.Summarizedtheoveralldemandsandlinkto the business plan and investment plan. 2.Rough-cutcapacity:Baseontheoveralldemandsand relativeinformation,calculatetherough-cutcapacityfor long term and midterm. Observe the load versus capacity chart,wecanfindtheloadtrendandcomeoutthe correspondingstrategytosolvethissituation.Thenlevel thepeakloadversuslowloadandreflecttothehuman resources plan.3.Materialrequirementplanning(MRP):Aftertheload levellingandapplyingthemanagementstrategies,the loadcanmatchdemandandbecomebalancedand feasiblesituation.Materialrequirementplanningsystem receivetheinputfromengineeringevaluation(Billof material,BOM),currentinventory(partlist,quantity), andcurrentcapacity(equipment,manpower),thencan come out the detail production schedule. DeliveryScheduleRutgh-CutCapacityEngineeringEvaluationMaterialRequirementPlanningInventory Part List Equipment ManpowerIn-houseFabricationDetail ProductionScheduleProcruement OutsourcingShop FloorControlDeliveryDemand IntegrationMaterial Logistics Figure 12 Management Process of MRO Company 0)%# Material .ogistics The material logistics include the following steps: 1.Detailproductionschedule:Afterthematerial requirement planning, we can obtain the detail production schedule. It base on the required lead time of detail parts, outsourcing parts, procurement partsetc., and figure out thefeasibleproductionschedule.Alloftheresources (material,manpower,machine)willsupportthe productionactivities.Especiallyspecificcritical parts/components may impact the assembly /maintenance progress need to close watch and control. IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge2/ .+ge2/ 2.Shopfloorcontrol:Thefabricationprogressofdetailparts andthemaintenancestatusofeachaircraftshouldbe monitorbyManufacturingExecutionSystem(MES)to fulfil the delivery schedule. The shop floor manager receive thedailyperformanceandprogressreportandarrangethe suitable resources to meet the detail production schedule. 3.Delivery:Aftertheassembly,functionaltest,andflight test,theaircraftcompletethemaintenanceschedule.It shouldpreparetherelativedocumentandqualityrecords for reviewing and approval. 0) Management 1stem TheManagementSystemofMROCompanyshouldinclude sevenkeymodules-CompanyObjectives,OrderManagement, Procurement Management, Inventory Management, Production Management,QualityManagement,RiskManagement,and show as Figure13. Figure 13 Key Modules of Management System ThedetailfunctionofKeyModulesforManagementSystem describe as following: 1.CompanyObjectives:Baseonthelongtermdevelopment planandmarketdemand,setuptheobjectivesforlong term,medium,andshorttermobjectivesofcompanyand functional department.2.OrderManagement:Integratetheorderscomefrom differentcustomers,managetheorderreceivingand deliveryandflowdowntherequirementtofunctional groups after harmonization.3.ProcurementManagement:Baseonthemasterproduction scheduleandprocurementthematerial/device/component, outsourcing the details to suppliers.4.InventoryManagement:Baseonthedemandquantityand unitpricetocategorizetheA-B-Ctypeofmaterial.Apply theRFID(RadioFrequencyIdentification)systemforthe inventory management.5.ProductionManagement:BaseontheMasterProduction Schedule(MPS)toproceedtheproductionactivities, monitorallthedetailpartsproductionandassembly progress.Includingmaintenanceplanning,manpower planning,materialplanning,machineandfacility planning,productionschedulingandcontrol, performance measuring.6.QualityManagement:Managethequalitysystem, operationprocedure,processcontrolandrelativequality document/recordanddispositiontosecurethereliability andsafety.Including:liaisonwithregulatoryauthority, inspectionmethodologyandstandards,qualityassurance auditetc.2)RiskManagement:Monitortheinternalandexternal environmentandmarket.Identifytheseverityand probabilityandpreparethemitigationplantogetridof the risk.3# 'ustomer 1atisfaction ThemainroleofanairlinesMROistoprovideafully serviceableaircraftwhenitisrequiredbytheoperatorsat minimumcostandoptimumquality.Principalactivities include:servicing,repair,modification,overhaul,inspection and determination of condition (Knotts, 1999). TheMROCompanyshouldfocusonthedelivery,quality, cost, and flexibility to meet the customer satisfactions, shows as Figure 14. Figure 14 Customer Satisfactions of the MRO Company 3)"# 4ualit The safety and reliability are the basic requirement of aircraft industry.TheMROCompanyshouldconstructintegrated qualitysystemtofulfilthedifferentaviationadministrators, aswellasdifferentairlines.Thus,itwillreducethe management cost and increase the overall revenue. 3)%# (eliver Theaircraftavailabilityisanimportantfactorfortheairline operation.TheMROCompanyshouldintegratethe maintenanceprocess,managementprocess,andmaterial logistics to meet the detail production schedule IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge20 .+ge20 TheMROCompanyshouldbuildtheriskmanagement mechanism to secure promised aircraft delivery schedule. Once raise potential risk, it need to prepare the action plan or backup plantomitigatetherisktosecurepromisedaircraftdelivery schedule. 3) 'ost The MRO Company should apply the lean concept to simplify thephysicalandinformationflowtoincreasethecost competitiveness. Wealsoneedtointroducetheconceptofsustainable development.Itcanutilizethesunlightthroughthehangar designtoincreasethebrightnessofworkspaceanddecrease electricenergyconsumption.Alsocollectthecleanenergy (solarenergy)byusingsolarpaneltosupportlightening system.BaseontheanalysisofIATA(ChrisMARKOU,2012),the average maintenance unit costs of narrow body aircraft is $893 perflighthour,showsasFigure15.Thebenchmarkof inventorylevelperaircraftofnarrowbodyaircraft,including A320 family, B737 classic and B737NG, the decreasing trends show as Figure 16. Figure 15 IATA Airline Average Maintenance Unit Costs of Narrow Body Aircraft (Chris MARKOU, 2012) Figure 16IATA Airline average maintenance unit costs of narrow body aircraft (Chris MARKOU, 2012) 3)* -le5ibilit# The MRO Company should develop the customized maintenance program to meet the policy and demand of different airlines to increase the revenue. The part fabrication shop or maintenance shop should reserve contingent capacity to react and tolerance some unpredictable issues. 2# 'onclusion Theaircraftmaintenance,repairandoverhaul(MRO)is important tothe airline operation. The C check and D check need the longer lead time and higher cost than A check and B check.ItisthegoodopportunityforprofessionalMRO Company to get the business from airlines.This study propose the Operation Management Model, which introducetheconceptofleanproductionandsustainable developmentintothemaintenanceprocessandmanagement process for MRO Company. TheMROCompanyshouldfocusonthedelivery,quality, cost, and flexibility to meet the customer satisfactions. 1.Quality:Constructintegratedqualitysystemtofulfilthe differentaviationadministrators,aswellasdifferent airlines.Thus,itwillreducethemanagementcostand increase the overall revenue. 2.Delivery: Integrate the maintenance process, management process,andmateriallogisticstomeetthedetail productionschedule.Alsobuildtheriskmanagement mechanism to secure promised aircraft delivery schedule. 3.Cost: Apply the lean concept to simplify the physical and informationflowtoincreasethecostcompetitiveness. Also introduce the concept of sustainable development to saving energy consumption. 4.Flexibility:Developthecustomizedmaintenance programtomeetthepolicyanddemandofdifferent airlinestoincreasetherevenue.Alsoreservecontingent capacity to react and tolerance some unpredictable issues. Thus, The MRO Company can increase the performance and competence in the competitive market. 6# References Chris MARKOU Assistant Director, IATA Operations, MRO AmericasApril2012,AirlineMaintenance:Industry Analysis and Trends, Esker,E.A.,Simpson,W.R.andSheppard,J.W.(1990),Air EmbeddedMaintenanceSub-Systems,ARINCResearch Corporation, Annapolis, MD. HamadAl-kaabi,AndrewPotterandMohamedNaim. (2007),AnoutsourcingdecisionmodelforairlinesMRO activities, Journal of Quality in Maintenance Heikkila,J.andCordon,C.(2002),Outsourcing:acoreor non-core strategic management decision?, Strategic Change, IJTEMT www.ijtemt.org; EISSN: 2321-5518; Vol. III, Issue II, Jue 2!1" Index Copernicus(ICValue: 6.14), #lri$%, &'(J, )(SE, *oogle S$%ol+r, J-*+te +, ($+,emi$ Jour+l &+t+-+se. .+ge28 .+ge28 Vol. 11, pp. 183-193. Massachusetts Institute of Technology (MIT), Lean Aerospace Initiative (2005), available at: www.lean.mit.edu MATTHIJS C. DlJKSTRA et al. (1994), Planning the Size and OrganizationofKLM'sAircraftMaintenancePersonnel, INTERFACES 24: 6, pp. 47-58. Knotts, R.M.H. (1999), Civil aircraft maintenance and support fault diagnosis from a business perspective, Journal of Quality in Maintenance Engineering, Vol. 5 No. 4, pp. 335-48. Rosenberg,B.(2004),Everybodysdoingit;airline maintenancestrategiesarediverse,butallincludeanelement of outsourcing, Aviation Week, 19 April, p. 68. Seristo,S.H.(1995),Airlineperformanceandcosts:an analysisofperformancemeasurementandcostreductionin majorairlines,PhDdissertation,HelsinkiSchoolof Economics Press, Helsinki. ShannonP.Ackert,2010,BasicsofAircraftMaintenance Programs for Financiers- Evaluation & Insights of Commercial Aircraft Maintenance Programs