因應燃油價格變動之航空網路航線機型與頻次規劃

Abstract

航空業營運深受外在環境影響，容易因為社經環境之變動蒙受巨額損失，其中由於燃油成本佔航空公司營運成本相當大的比例，但國際油價容易受到國際局勢、油產國聯合減產或是匯率波動等因素之影響，具有極大之不確定性，使航空公司對於燃油成本之控制更形困難。實務上航空公司透過減班、取消航線等方式降低成本因應油價上升之衝擊。透過航空網路設計規劃，航空公司可於規劃期間，評估其機隊組成與航線旅運量，規劃適當之機型頻次以滿足旅運量需求。過去關於航空網路規劃問題之研究極少討論營運成本之不確定性對於航空公司規劃航線機型頻次之影響。關於油價變動之研究，過去則多就經濟與金融層面進行探討，少有研究就航機之燃油價格與航空網路成本進行分析。本研究即針對航空燃油價格特性深入探討，並分析航空公司如何因應燃油價格變動進行航空網路規劃最適之航線機型頻次。 本研究以航空公司客運之營運成本組成結構為基礎，建立航空網路規劃模式，在營運成本最小化之目標式下，求解網路之航線機型與頻次。進而考慮燃油價格之變動為航空公司難以預測與控制之不確定性因素，以區間分析的概念分析燃油歷史價格特性，假設燃油價格在不同區間之下呈現常態分配的情形，以作為計算各航線可靠度之參數，本研究定義可靠度為初始規劃機型頻次下，航空公司可維持航油成本收支損益平衡之機率，並且建構可靠度模式。在求解網路規劃模式之後，針對各航線規劃之機型頻次，以可靠度模式評估其規劃在油價變動下維持其燃油成本損益平衡之機率，做為航空公司因應航空燃油之變動決策是否進行調整策略之依據，並假設不同情境下之調整策略，如因應燃油價格變動與需求變動重新規劃、加入新型航機重新規劃、引入實際旅運需求變化量，經由放鬆限制式重新規劃航線與頻次，同時評估期調整成本與懲罰值，提供航空業者因應不確定性因素下之評估及決策方法，減少外在因素影響下之營運虧損。 本研究透過範例分析進行模式之求解與操作，並以2007年與2008年之航機燃油價格與旅運量進行實證分析，研究結果顯示，本研究模式在航線規劃上選擇轉機航線，各航線偏向選擇直接成本較低之機種，模式具有決策最小成本之規劃功能，以多種機型規劃後，機型選擇符合目前航機之設計與採用趨勢。本研究分析航機燃油歷史價格在不同油價區間下，其分佈具有常態分配之特性。根據範例分析，當油價發生異常上升情形則航線之可靠度下降，油價異常下降則造成可靠度上升，再權衡懲罰值與調整成本進行決策是否調整，結果顯示，置換航機後之可靠度評估則顯示使用新型航機具有提高頻次、節省燃油成本之效果，承載率高之長程航線採轉機航線較具有節省燃油成本之效益，並提高短程航線之承載率與服務頻次。綜合上述，航空公司可衡量本身機隊條件、各航線特性與燃油價格特性，規劃決策最適之航線、機型與頻次，以降低燃油成本對營運之衝擊。

Airlines face the severe challenge of jet fuel price uncertainty because of the difficulties in controlling the fuel cost. When the fuel price is raised in an escalating rate, airlines might adjust their network operations such as decreasing flight frequency or cancelling routes with markedly negative profit. With the airline network design, carriers can determine the appropriate aircraft types and flight frequency for each route to meet the passenger demand. Though a number of studies have discussed the network design problem considering the uncertainty of passenger demand, few of those dealt with fuel price. This study develops a series of models to determine the aircraft types and flight frequencies on individual routes, and evaluate the reliability of the proposed network planning under the fluctuation in jet fuel price. Furthermore, the adjustment and decision-making method is provided to decide whether to adjust flight frequencies or remain the initial planning in response to fuel price fluctuation. Airline network design model is used to determine the types of aircraft and flight frequencies on individual routes with the objective of minimizing airline network operation costs. To evaluate the reliability in airline network, the study further assumes historic data of fuel prices can be classified into distinct intervals within each of which there exists a normal distribution. The fuel-price intervals and distributions have been calibrated and used as critical parameters for reliability evaluation. In this study, the reliability of individual routes are based on whether revenues from flights with initially proposed flight frequencies and aircraft can accommodate for variations in jet fuel expenditure. We define the reliability as the probability that the proposed flight frequencies will operate in an at least break-even condition under future fuel price fluctuation. This study further provides a number of adjustment methods to adjust the unreliable network under different situations.We examine the influence of fuel price and passenger demand on the reliability of airline network using sensitivity analysis. The adjustments include changes in flight frequency and exiting aircraft and the purchase of new fuel-efficient aircraft. Two case studies are presented to examine the feasibility of the models. The first case uses the forecasting demand and fuel price to evaluate the reliability of network in response to future uncertainty. The results provide adjustment suggestions in dealing with a combination of passenger demand and fuel price with varying fluctuation rates. The second case uses the real data of an international carrier in Taiwan as an example to illustrate how to deal with turbulent fuel price and economic situation in 2007 and 2008. The results show the critical load factors for unreliable routes, which enable airlines easily identify routes to adjust flight frequency and/or aircraft, thereby reducing the expected losses during the fuel price fluctuation periods. In sum, the results of the study provide ways to enhance the commercial airline network design in response to future uncertainty of jet fuel price and improve the decision-making of network planning and adjustment.