航空公司機隊規劃之航機採購/汰換時程之研究

Abstract

航空市場的發展與經濟情況盛衰、景氣循環有相當密切的關係，近年來亞洲地區經濟不景氣，使得亞洲地區的航空公司為了應變市場縮減及有效運用公司資金，紛紛對飛機製造商取消了之前的飛機訂單，根據Woolsey（1999），至1998年10月底，波音公司就被取消了36架新飛機的訂單。由上述的例子可了解，航空公司的機隊採購與汰換時程決策對航空公司整體營運況狀具有重大影響，因此如何決定最佳機隊購置汰換時程，以創造最大之航空公司利潤即為相當重要的議題。過去有關航空公司機隊管理之相關文章多半著墨於機型選擇、機隊與航線間的指派、或機隊飛機利用情況對購買新飛機和淘汰舊飛機的影響，並未將機隊購置汰換時程之影響因素考量於決策模式中。航空公司之機隊購置/汰換時程與公司之資金運用、營運策略研擬及資產利用息息相關，若航空公司能夠在較佳之時間進行機隊更新，將能使資金運用更靈活、資產利用更充分，為航空公司創造最大利潤。 本研究由航空公司之觀點探討機隊採購/汰換的最佳時程，考量航空公司營運成本、及機隊更新決策之成本，配合機隊飛機之利用率，藉由解析性方法推導建構航空公司之直接與間接營運成本及機型選擇、汰換決策之函數。在經濟景氣循環影響航空旅客需求方面，則應用灰色理論之拓撲預測（Grey Topological Forecasting）（鄧聚龍，1986），以航線旅客流量及景氣循環波形歷史資料推估未來可能之航線旅客需求量及經濟景氣波動情況之變化機率。本研究以動態規劃構建機隊規劃數學模式，以最小化航空公司之期望成本為目標，將灰色拓撲所預測出之旅客量以馬可夫鏈模式作校正後，依其經濟循環波形切割為不同之景氣時區，在各時區之旅客需求亦分別被滿足的情況下，可得知航空公司之最佳機隊更新決策及時程。航空公司在不同時程所做的機隊規劃在未來預測之旅客量下，景氣佳時的高機隊利用率在景氣差時則可能出現資產閒置而影響營運成本及收益的情形；且在不同時程之舊機淘汰殘值與購買新機花費間的權衡取捨亦影響航空公司之利潤。 本研究之結果顯示航空公司之機隊航機購置/汰換時程會對航空公司之營運成本造成影響，而航空公司對未來所做的預測越準確，則其期望成本會較小。由本研究的實證分析中可知，舊航機與新航機之間存在有一置換的臨界成本；而新型航機與舊型航機間亦然；另外航空公司租賃航機之金額與購買航機之折舊金額也有一決策之臨界值，在灰色拓撲預測配合馬可夫鏈轉移機率模式校估航空旅客需求量方面，則得到適配度很高的預測模式，且該模式的確能夠反映經濟景氣之循環。本研究結果可提供航空公司面臨不同景氣需求時，在航空公司之成本、對未來旅客流量之預測及機隊飛機利用率各項交互作用下，決定航空公司之最佳機隊採購/汰換時程。本模式除了可供航空公司在決策機隊更新或淘汰時做參考外，亦可提供飛機製造商研擬能夠配合經濟景氣之生產策略。

The development of airline market is closely related with economic cycle, i.e., airlines in Asia canceled their orders to aircraft manufacturer one after another in past few years since the economic recession in Asia area. The performance of airline is deeply influenced by aircraft purchase and replace scheduling, therefore it’s important for airline to make the best strategy of aircraft purchase and replace scheduling for obtaining the yield. Previous literature on fleet planning usually focused on fleet assignment, maintenance planning and buy or lease decisions etc. However, no literature has combined aircraft purchase and replace scheduling and economic cycle to formulate theoretical model on analyzing aircraft purchase and replace scheduling in response to passenger demand fluctuation. So airlines may re-arrange its aircraft purchase and replace scheduling considering passenger demand fluctuation for getting more yield. This research aims to investigate the operation cost, aircraft purchase and replace scheduling cost, and maintenance cost, to explore the best aircraft purchase and replace scheduling for airline. The study identifies airline cost function and formulates an model by minimizing airline operation cost in dynamic programming model to determine the optimal aircraft purchase and replace scheduling in response to passenger demand fluctuation. Furthermore, the study discusses the context of aircraft type choosing, and investigates the impact of different aircraft ages and mileage to the scheduling and operation cost. Since the passenger demand fluctuation will influence yield of airline. Therefore, the study further uses Grey Topological forecasting model and Markov Chain to forecast future passenger demand and probabilities of demand fluctuation. Furthermore, the study makes segmentation of passenger demand according to economic cycle, to formulate a model deciding the strategy of aircraft purchase and replace scheduling by minimizing the airline operation cost in dynamic programming model subject to satisfy passenger demand. An empirical example is provided to illustrate the application of the model and to show its usefulness. The aircraft purchase and replace scheduling is effected by aircraft purchase cost, lease cost, maintenance cost and aircraft types from the result. Finally, sensitive and scenario analyses are implemented to demonstrate the effects of variations in key variables to aircraft purchase and replace scheduling and operation cost, such as aircraft purchasing cost, aircraft leasing cost etc. It is envisaged that the results of the developed models not only can decide the aircraft purchase and replace scheduling, but also provide guidance on tradeoff between old crafts and new crafts, for airlines to re-arrange its’ fleet in response to passenger demand fluctuation.