航空網路中航班延誤之因果模式

Abstract

航班延誤由於會造成航空公司與旅客的不便和額外之成本，因此為一值得關心之議題，本研究旨在針對航機於多機場間之延誤擴散及航空公司之改善延誤的方法之效果提出分析方法。由於航班之地面與空中運作存在隨機變化的特質，本研究分析航班之抵達與離開機場之延誤背後的因素，以釐清航空公司之班表運作過程中各階段可能受到的干擾因子。 本研究利用一家台灣之航空公司的國內線航班資料，以Cox等比例危險模式構建航班抵達與離開機場之延誤模式，本模式可顯示在航班運作過程中之航班延誤擴散的形成。分析結果顯示，起飛之航班所受到的延誤因素較多，相對而言，抵達機場的航班所受到的影響因素主要為氣候及航路與擬降落機場的航管因素，因此，大部分抵達機場的航班之延誤除了起飛機場已形成的延誤外，均非航空公司所能控制，隱含的意義為避免起飛機場的延誤才是根本解決抵達延誤的有效方法。本研究所求出的危險比例可用來衡量在不同情境下延誤的航班恢復正常運作的機會大小，並可分析個別的延誤影響因子對於航空公司班表的可靠度之影響程度。 為減少航班延誤所造成的影響，航空公司無不積極投入地面與空中運作的不確定性事件之預防工作，因此，本研究進一步利用所構建的航班抵達與離開機場之延誤模式，分析航空公司所採取的改善延誤之方法的有效性，其中包括對於縮短地面作業時間及增加地面與空中運作的緩衝時間之效果的評估，主要的作法為針對投入改善的成本和所減少的延誤之利益進行淨效益的估算。 雖然增加緩衝時間可以減少一些航班的延誤時間，研究發現在考量到緩衝時間的成本之情況下，這種改善延誤的作法對航空公司不一定有利，研究結果並發現，在動態的運作環境中，增加緩衝時間不一定能大幅改善航班的延誤狀況。因此，航空公司可能需要進一步分析真正影響航班延誤的背後之主要因素，在採取許多複雜的改善方法之前，應該先有一套適切的延誤管理計畫。本研究對於航空公司班表與航班延誤擴散之關係提供進一步的了解，因此，對於班表運作的控制及延誤的管理有相當大的助益。

Flight delays are a source of great concern as they generate disruptions and increase costs for airlines and passengers. The aim of this research is to propose approaches to examine flight delay propagation in a multiple-airport environment and to evaluate the effectiveness of delay improvement schemes adopted by airlines. Due to the stochastic characteristics of turnaround and block operations, this research investigates the factors behind the mechanisms of departure and arrival delays to clarify the phases and activities involved in flight delays through an airline schedule. The Cox proportional hazards model, a method widely applied in survival analysis, is used to develop departure and arrival delay models involving a Taiwanese domestic airline. The proposed models show how flight delay propagation can be formulated through repeated chain effects in aircraft rotations. The results shows that whilst outbound flights are subject to a wider range of difficulties leading to delays, inbound flights can be delayed by weather or air traffic control restrictions en-route or at destination airport. Hence, most arrival delays are beyond the control of airlines except for delays that develop at departure airports. This implies that developing the means to prevent departure delays could be the key to reducing arrival delays from the origin. The hazard ratios obtained provide measures of the chances of recovering from flight delays under a variety of situations and the effects that individual contributing factors of flight delays have on airline schedule reliability. To manage flight delays, airlines are prepared for the unexpected stochastic events of turnaround and block operations. This research further uses the obtained departure and arrival delay models to examine delay improvement schemes, including shorting required ground handling time and increasing buffer time for turnaround and en-route aircraft. The costs of schemes and the savings of delay costs are investigated to evaluate the net benefits of schemes by recursively combining the departure and arrival delay models. Though buffer time may save some delays, it is found that it may not be cost effective for airlines when the costs of buffer minutes are taken into account. The results also reveal that delays may not be greatly improved through this measure in the dynamic operating environment. Thus, airlines may investigate the significant contributing factors of delays and design a suitable delay management program before jumping into some sophisticated measures. The findings provide a better understanding of the relationship between planned schedules and delay propagation, and are thus useful for schedule control and delay management.