外部經濟因素對航空公司飛機持有之影響

Influence of External Economic Factors on Aircraft Ownerships in Airlines

飛機是航空公司營運主體，購置成本高，其性能良窳也和航空公司營運成本占比極高的油料費用支出密不可分。決策者對飛機持有的思維，除內部營運考量外，也與外部因素息息相關。本研究以華航和長榮為研究對象，藉由資料蒐集和存活分析理論，探索其飛機持有的特質，並研析匯率、利率、油價與國內生產毛額 （Gross Domestic Product, GDP）四項外部經濟因素，對兩家公司飛機持有時間的影響。從存活函數分析中發現，長榮相較華航更替飛機的速度為快，且常以機型為單位來汰換飛機，機型持有種類較為單一。Cox比例危險模型檢定結果顯示，華航在飛機持有上較不受外部經濟因素影響，但長榮會受GDP波動左右。變數門檻改變之敏感度分析，則確定匯率非兩家公司考慮飛機持有的關鍵因素。

Aircraft play a main role in airline operations. They have high purchased costs. Their operational performance also affects the fuel expense that shares a larger percentage of airline operation costs. Decision makers normally consider not only the inner operation conditions but also external factors for keeping aircraft ownerships. This study, focused on China Airlines and EVA AIR, collected related data and used survival analysis to explore their behaviors on holding aircraft. Four external economic factors including exchange rate, interest rate, fuel price, and gross domestic product (GDP) were examined for the influence to the duration of holding aircraft in operation. The findings from survival functions revealed that EVA hold less types of aircraft fleet and replaced aircraft, or even an entire type of fleet, faster than China Airlines. Test results of the Cox proportional hazards model revealed that the decision of China Airlines was not affected by those external economic factors, while EVA's decision was influenced by the changes of GDP. The sensitivity analysis with settings of different thresholds for variables can ensure that the exchange rates unaffected the decision of these two airlines.