This chapter consists of four sections. Section 1.1 addresses the background and motivation of analyzing flight delay propagation and evaluating delay improvement schemes. The research objective is presented in Section 1.2. Research scope and research framework are introduced in Sections 1.3 and 1.4, respectively.
1.1 Background and Motivation
Flight delays are a source of great concern because they generate disruptions and costs to airlines, airport operators, ground handlers and passengers. A common assumption in airline schedule planning is that flights will operate as planned. However, aircraft rotations among airports can be disrupted by many factors, such as delays at previous airports, weather, mechanical or logistical problems with aircraft, late-boarding passengers, and late-arriving crews, and therefore this optimistic situation rarely occurs.
Flight delays may occur at different phases of aircraft rotations. When an aircraft is delayed, the airline suffers delay costs since the aircraft and crew in service are fixed in the schedule. Passengers surely are also dissatisfied with the delayed flight and change their loyalties towards the airline due to the unpunctuality of the schedule. Passenger complaints concerning delays, cancellations, and denied boarding have prompted the U.S. Congress to consider stronger measures to ensure passenger protection (U.S. Government Accountability Office, 2011). Of the total delay costs analyzed by Austrian Airlines, only 22% can be attributed directly to the effect of delays. In fact, 24% of these costs come from the permanent loss of passenger loyalty and 54%
come from induced knock-on delays in aircraft rotation schedules (Airline Business, 1999). United Airlines estimated that it saved approximately $1.6 million by using a flight delay projection model during the first quarter of 2004 (Abdelghany et al., 2004). Both of these cases suggest that the consequences of delays and their propagation in the air transport system, including decrease of
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productivity of aircraft as well as loss of time and loyalty of passengers, cannot be neglected.
The general optimization objective of schedule planning is to reduce flight delays while maximizing the utilization of aircraft. Certainly, airlines may or may not be able to control delay causes. Since delays occur randomly, airlines often embed buffer time to schedules for turnaround and block operations to account for stochastic characteristics of delays. Nevertheless, delays will occur when the accumulated delays exceed scheduled buffer time. Though the scheduling of buffer time stabilizes schedule punctuality and reduces delay costs, airlines may incur costs of additional resources by using this improvement measure. The benefits of delay improvement therefore need to be further investigated.
In aircraft’s daily operations, delays in one flight might easily propagate to successive flights to have further disruptions. Accordingly, how to obtain the overall effects of an initial flight delay in an airline schedule is essential to solve the problem of flight delays. To achieve this goal, airlines have to understand the mechanisms of flight delay propagation as well as to find out the way to identify the origins and effects of flight delays.
1.2 Research Objective
The objectives of this research include:
1. Propose an approach to explore the problem of flight delay propagation in a dynamic operating environment by considering the stochastic characteristics of turnaround and block operations and clarifying the relationship between flight delays and the associated causes:
The duration of a delay represents a period of time the delay has survived before it comes to an end. To fit the survival characteristics of flight delays, survival analysis is employed to model flight delays in a multiple-airport environment.
2. Propose an approach to evaluate the effectiveness of delay improvement schemes by exploring the costs invested for delay improvement and the
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costs of delay saved:
Because arrival and departure delays are stochastic in nature, delay costs need to be investigated by calculating the expected costs incurred in the delays. Thus, an approach including survival distributions of flight delay propagation in an airline network and the associated expected delay costs will be developed. The incurred delay costs will then be used to compare with the costs invested for delay improvement to evaluate the effectiveness of delay improvement schemes.
1.3 Research Scope
This research is to explore the problem of flight delay propagation in airlines’ daily operation network. To find out the way to reduce flight delays, the party of interest in this research is airline companies instead of airports. The historical data collected was scheduled flights, which included delayed and on-time flights, collected from a Taiwanese domestic airline. In addition, to explore the effects of flight delay propagation, we need the information of an extensive flight network with a very high frequency of flights. Thus, the analysis will focus on only its domestic air routes. International air routes operated by the company will not be analyzed in this research. The general problems, including departure and arrival delays, will be the main subjects to be addressed. By combining the effects of departure and arrival delays, flight delay propagation in an airline network can be therefore investigated through repeated chain effects.
1.4 Research Framework
Given the objectives, the research framework is illustrated in Figure 1.1.
Chapter 1 explains the background of flight delay problems existing in airline operations and the motivation to find out the way to solve the problems. The objectives and scope of the research are then defined. Prior to analyzing the problems of flight delays, Chapter 2 reviews the studies and applications regarding types and causes, assessment and forecast, and control measures of
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flight delays to have a better understanding of the relevant issues. Research regarding system costs incurred in flight delays is also reviewed. Chapter 3 first discusses flight delay mechanisms to identify the relationship among flight delays. Two approaches to explore the problem of flight delay propagation are then presented. The first one is to model flight delays in an airline network. The second one is undertaken to analyze the effectiveness of delay improvement schemes using the flight delay models obtained by the first approach. Chapter 4 shows the empirical study using a historical flight data collected from a Taiwanese domestic airline. Chapter 5 makes the conclusions and suggestions.
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Figure 1.1 Research framework.
Identification of research objectives
Development of research methodology
An approach for evaluating delay improvement schemes An approach for
modeling flight delays
Empirical study
Chapter 1Chapter 2Chapter 3Chapter 4Chapter 5
Literature Review
◆Types and causes of flight delays
◆Assessment and forecast of flight delays
◆Control measures of flight delays
◆System costs of flight delays
Flight delay mechanisms
Conclusions and suggestions
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