Minimizing takeoff and landing risk in helicopter pickup and delivery operations

The problem of minimizing total helicopter passenger risk caused by takeoffs and landings is studied. There are passenger pickup and delivery demands to be satisfied at given points by flights starting and ending in the same heliport and visiting several points. For each point, the delivery demand is the number of passengers to be transported from the heliport to this point and the pickup demand is the number of different passengers to be transported from this point to the heliport. Each pickup and delivery demand must be satisfied in full by one flight. There are an upper bound on the number of flights and an upper bound on the helicopter passenger capacity. The objective function is a linear combination of the numbers of passengers involved in takeoffs and landings at visited points. A solution is characterized by the number of flights, sets of visited points and their sequences for all flights. Properties of optimal solutions are established. Several cases are proved NP-hard. A quadratic boolean programming formulation and two dynamic programming algorithms are suggested for the general case. Computer experiments demonstrated that they are able to solve real-life instances. Polynomial time algorithms are presented for special cases. Implementation of the suggested solutions into the real helicopter operations should decrease the number of fatalities.     

A Grasp for Aircraft Routing in Response to Groundings and Delays

This paper presents a greedy randomized adaptive search procedure (GRASP) to reconstruct aircraft routings in response to groundings and delays experienced over the course of the day. Whenever the schedule is disrupted, the immediate objective of the airlines is to minimize the cost of reassigning aircraft to flights taking into account available resources and other system constraints. Associated costs are measured by flight delays and cancellations.In the procedure, the neighbors of an incumbent solution are generated and evaluated, and the most desirable are placed on a restricted candidate list. One is selected randomly and becomes the incumbent. The heuristic is polynomial with respect to the number of flights and aircraft. This is reflected in our computational experience with data provided by Continental Airlines. Empirical results demonstrate the ability of the GRASP to quickly explore a wide range of scenarios and, in most cases, to produce an optimal or near-optimal solution.     

Obtaining the optimal fleet mix: A case study about towing tractors at airports

Planes do not have a reverse gear. Hence, they need to be towed by tractors when leaving the gate. Towing tractors differ with respect to investment as well as variable costs and plane type compatibility. We propose a model which addresses the problem of a cost minimal fleet composition to support towing service providers in their strategic investment decisions. The model takes into account a maximum lifetime, a minimum duration of use, an overhaul option and a sell option. In a case study with a major European airport (our cooperating airport) we generate a multi-period fleet investment schedule. Furthermore, we introduce a 4-step approach for demand aggregation based on flight schedule information. We analyze the impact of demand variation, flight schedule disruptions and cost structure on the optimal buy, overhaul and sell policy. The scenario analyses demonstrate the robustness of the investment schedule with respect to these factors. Ignoring the existing fleet, a green field scenario reveals saving potentials of more than 5% when applying this model.     

Probabilistic Analysis of Domino Effects by Using a Matrix-Based Simulation Approach

Major industrial accidents occurring at so-called major hazard installations may cause domino accidents which are among the most destructive industrial accidents existing at present. As there may be many hazard installations in an area, a primary accident scenario may potentially propagate from one installation to another, and correlations exist in probability calculations of domino effects. In addition, during the propagation of a domino effect, accidents of diverse types may occur, some of them having a synergistic effect, while others do not. These characteristics make the analytical formulation of domino accidents very complex. In this work, a simple matrix-based modeling approach for domino effect analysis is proposed. Matrices can be used to represent the mutual influences of different escalation vectors between installations. On this basis, an analysis approach for accident propagation as well as a simulation-based algorithm for probability calculation of accidents and accident levels is provided. The applicability and flexibility of this approach is discussed while applying it to estimate domino probabilities in a case study.     

基于峰值负荷的签派员席位任务分配问题

本文研究的问题来源于航空公司运行控制中心的签派部门,签派员在放行航班时,既要保证航班的正点起飞,又要调节放行航班的工作劳动强度保证放行的质量,使航班在安全状态下运行。这里放行航班的工作劳动强度为单位时间内的工作时间,峰值负荷即劳动强度最大值。峰值负荷过高则工作紧张,进而推断该放行席位的任务分配不合理。文中将问题描述为任务有优先序的单机排序问题,每个任务都有一个到达时间（release time）、截止期限（deadline）和处理时间（procession time）,处理时间因任务的不同而不同,目标是在绝对不准延误完成任务前提下,使单位时间的峰值负荷最小。在使单位时间峰值负荷最小的目标下,本文提出了一个有效算法,并证明该算法下的任务安排是最优安排。     

Solving the flight gate assignment problem using dynamic programming

This paper considers the problem of assigning flights to airport gates—a problem which is NP-hard in general. We focus on a special case in which the maximization of flight/gate preference scores is the only objective. We show that for a variable number of flights and gates, this problem is still NP-hard. For a fixed number of gates, we present a dynamic programming approach that solves the flight assignment problem in linear time with respect to the number of flights. Computational results using real life data from a major European airport prove the practical relevance of this approach.     

考虑延误因素的机组排班模型研究

机组排班是航空公司运营计划的重要环节。传统对机组排班问题的研究,通常不考虑延误对排班的影响,导致机组排班的鲁棒性较差。本文在传统机组排班模型的基础上考虑延误成本,以最小化各项任务成本和延误成本为目标,提出了考虑随机延误因素的机组排班数学规划模型。然后提出求解此模型的启发式列生成算法,该算法可有效缩小问题规模,减少求解过程中的迭代次数并提高求解质量。利用航空公司真实飞行数据进行测试,证明算法可在短时间内求解大规模机组排班问题。最后,通过仿真试验证实考虑延误的机组排班模型可有效提升排班的鲁棒性。     

Scheduling Truck Arrivals at an Air Cargo Terminal

We consider the scheduling of truck arrivals at an air cargo terminal. By coordinating arrivals of cargo delivery trucks with outbound flight departure schedules, some of the shipments can be transferred directly to the departing flights, while others will be stored at the terminal's storage facility and incur extra handling and storage costs. The objective is to obtain a feasible schedule so as to minimize the total cost of operations. We formulate the problem as a time‐indexed integer program and show that, even with limited number of unloading docks at the terminal, the problem is non‐trivial (NP‐hard in the strong sense). Our solution method includes an exact solution procedure to determine an optimal unloading sequence for the shipments carried by each truck, together with a Lagrangian relaxation‐based heuristic for assigning trucks to truck docks and determining truck arrival times. We conducted computational experiments to test the performance of our solution method. Computational results show that our method can generate near‐optimal solutions efficiently. Our simulation results indicate that the scheduling approach proposed in this paper has the potential to generate significant cost savings over a first‐come, first‐served approach currently used at the air cargo terminal that we observed.     

Assessing fairness of selfish revenue sharing mechanisms for airline alliances

Airline alliances offer flights including flight legs operated by different airlines. A major problem is how to share the revenue obtained through selling a flight ticket among the airlines in a fair way. Recently, Kimms and Çetiner [1] have proposed fair revenue allocations based on the solution concept nucleolus, which assumes that the decisions of the alliance are given centrally. However, in an alliance, each airline has a selfish behavior and tries to maximize its own revenue. The contribution of this paper is twofold. First, we provide a method to evaluate the fairness of revenue sharing mechanisms applied in a selfish setting. The method includes a simulation model for the booking process of the alliance and uses the nucleolus-based allocations as benchmark. Second, we develop a revenue sharing mechanism based on the transfer of dual prices. The fairness of the new mechanism and several other existing approaches is assessed through a numerical study.     

基于Fisher聚类算法的航班飞行高度偏差分析研究

目前计算机飞行计划(Computerized Flight Plan,CFP)中的计划飞行高度与实际飞行高度之间存在偏差.为了能识别出航路中易发生显著偏差的子航段,便于对其进行重点监控,本文提出一种基于Fisher有序样本聚类算法的航班飞行高度偏差分析方法,采用修正的Fisher有序样本聚类算法对航路进行分段,在分段的基础上,对每个子航段上的高度偏差平均水平及波动情况进行统计分析,作为高度偏差的评价指标.分析结果可帮助识别航路上易发生显著实际与计划飞行高度偏差的子航段,为签派人员制作飞行计划以及在机组人员进行航前准备提供决策依据,具有较好的实践意义.     

Passenger and pilot risk minimization in offshore helicopter transportation

In the offshore petroleum industry, employees are transported to and from the offshore installations by helicopter, which represents a major risk. This paper analyzes how to improve transportation safety by solving the helicopter routing problem with a risk objective expressed in terms of expected number of fatalities. A mathematical model is proposed and a tabu search heuristic is applied to this problem. Three routing policies are considered: a direct routing policy, a Hamiltonian routing policy, and a general routing policy. Extensive computational experiments are conducted on instances derived from real data in order to assess and compare these policies under a travel time, a passenger risk and a combined passenger and pilot risk objective. Several management insights can be derived from this study. In particular, our results show that passenger transportation risk can be reduced by increasing travel time at the expense of pilot risk. This can be achieved through a reduction of the average number of passengers onboard by applying either a Hamiltonian or a general routing policy. Our methodology can also be used to derive an equitable distribution of risk between passengers and pilots, considering that pilots fly much more frequently than passengers.     

The relationship between burnout and risk-taking in workplace decision-making and decision-making style

This study aimed to investigate what decision-making styles might be exhibited by employees who experience burnout. Using a Work Risk Inventory (WRI), developed for this study, which included generic workplace scenarios, it was also explored whether such employees take relatively more risky decisions. Risk was conceptualised as the adoption of decisions that threaten one’s reputation at work, job performance and job security. The mediating effect of the likelihood and seriousness of the consequences of the worst that could happen in each given scenario on the relationships between dimensions of burnout and risk-taking was also tested. A total of 262 employees in various occupations completed an online survey, including measures on burnout, decision-making styles and the WRI. As predicted, dimensions of burnout – exhaustion, cynicism and professional inefficacy – correlated significantly with avoidant decision-making and negatively with rational decision-making. The seriousness of the consequences of the worst-case scenario occurring mediated the relationship between professional inefficacy and risk-taking. In the context of identifying mechanisms by which burnout leads to risky decision-making, the findings suggest that employees’ sense of professional inefficacy determines their risky decision-making. The contribution to theory and implications for practice are discussed.     

Risk Perceptions of Offshore Workers on UK Oil and Gas Platforms

Knowledge of the workforce's risk perceptions and attitudes to safety is necessary for the development of a safety culture, where each person accepts responsibility for working safely. The ACSNI Human Factors report stresses the importance of assessing workforce perceptions of risk to achieve a proper safety culture. Risk perception research has been criticized for insufficient analysis of the causal relationships between risk factors and perceived risk. The present study reports some of the factors which predicted risk perception in a sample of 622 employees from six UKCS offshore oil installations who completed a 15-section questionnaire. This paper focuses on the accuracy of workers' risk perceptions and what underlying factors predict the perception of personal risk from both major and minor hazards.     

Heuristic approaches for flight retiming in an integrated airline scheduling problem of a regional carrier

Flight retiming in airline scheduling consists in slightly modifying the scheduled departure time of some flights with the goal of providing a better service with a cheaper cost. In this research, the departure times must be selected from a small discrete set of options. The whole problem embeds flight retiming, fleet assignment, aircraft routing and crew pairing. Thus, the aim is to determine the departure times of the flights, the fleet assignment and the minimum cost aircraft and crew routes. The objective function takes into account a large cost associated with each crew member, a penalization for short or long connection times, a cost for crew members changing aircraft along their routes, and a minor penalty associated with the use of each aircraft. The constraints enforce aircraft maintenance and crew working rules. In this setting, flight retiming is allowed to potentially reduce the total costs and increase the robustness of the solution against delays by decreasing the number of aircraft changes.We propose and compare four heuristic algorithms based on a Mixed Integer Linear Programming model for the whole problem. The model contains path variables representing the crew pairings, and arc variables representing the aircraft routes. In the heuristic algorithms, column generation is applied on the path variables, and different flight retiming options are considered. The algorithms are tested on real-world instances of a regional carrier flying in the Canary Islands to evaluate their advantages and drawbacks. In particular, one of the algorithms, that uses the solution of the Linear Programming relaxation of the model to select promising options for the departure of the flights, turns out to be the most effective one. The obtained results show that costs can be significantly reduced through flight retiming while still keeping the computing times reasonably short. In addition, we perform a sensitivity analysis by including more retiming options and by using different aircraft and crew costs. Finally, we report the results on larger size instances obtained by combining real-world ones.     

IMPLICIT OPTIMAL AND HEURISTIC LABOR STAFFING IN A MULTIOBJECTIVE,MULTILOCATION ENVIRONMENT*

This paper presents a tractable set of integer programming models for the days-off scheduling of a mix of full- and part-time employees working α to β days/week (cycle) in a multiple-objective, multiple-location environment. Previous models were formulated to specifically schedule part-time employees working either two or three days per week. These models were intractable because they required complete employee schedule information. The new models are deemed implicit optimal since they are required to supply only essential information. While the number of variables in previous models is an exponential increasing function of β-α, the size of three of the new models is independent of α and β. The first three models developed here (as in [18]) deal with the trade-offs between idle time, the number of employees required to work at multiple “locations,” and the size of the total labor pool. The inherent flexibility of the implicit modeling approach is illustrated by the presentation of various modifications of the basic models. These modifications permit the use of preference weights on the number of employee work days/week (cycle) or the minimization of payroll costs where differential pay rates exist. These latter models may also be formulated such that idle time is ignored, constrained or minimized. The execution time for the implicit models (on a CDC CYBER 730 computer with commercially available software) averaged well under five seconds on 1200 trial problems for the type of application considered in [18]. A solution was obtained in less than 46 seconds of CPU time for a trial problem which would have required over 1.4 million integer variables with previous models. The availability of optimal solutions was invaluable in the development of two heuristics designed to deal with the trade-offs of [16]. In an experimental analysis a previous heuristic produced results which averaged from 74 to 508 percent above optimum across six experimental conditions. The comparable new heuristic produced results which averaged from 3 to 8 percent above optimum for the same experimental conditions. The paper concludes by developing a framework to integrate the results of this research with the tour scheduling problem and by identifying several other areas for related research.     

PRODUCTION SCHEDULING OF CONTINUOUS FLOW LINES: MULTIPLE PRODUCTS WITH SETUP TIMES AND COSTS

The problem of production planning and setup scheduling of multiple products on a single facility is studied in this paper. The facility can only produce one product at a time. A setup is required when the production switches from one type of product to another. Both setup times and setup costs are considered. The objective is to determine the setup schedule and production rate for each product that minimize the average total costs, which include the inventory, backlog, and setup costs. Under the assumption of a constant production rate, we obtain the optimal cyclic rotation schedule for the multiple products system. Besides the decision variables studied in the classical economic lot scheduling problem (ELSP), the production rate is also a decision variable in our model. We prove that our solutions improve the results of the classical ELSP.     

飞行频率、拥挤成本和互补型航空联盟:中枢轮辐网络机场拥挤分析

本文在基于飞行频率、拥挤成本和互补型航空联盟的基础上系统分析了中枢轮辐网络机场拥挤问题。研究表明:航空公司的利润最大化使得航班飞行频率存在过度供给,飞机大小也是次优的,这进一步恶化了中枢机场的机场拥挤;航班飞行频率与航空公司的拥挤成本系数、旅行计划延迟效用系数正相关,与飞机每次起降的固定成本负相关;互补型航空联盟使得联盟体利润增加,航空联盟对连接市场乘客有利,对本地市场乘客不利,航空联盟还可以内化伙伴间拥挤,航班飞行频率得以优化,机场拥挤得以缓解。     

The linkage between human resource practices and organizational ambidexterity: An analysis of internal labor market dynamics in a port-of-entry context

This paper presents our findings from an empirical survey of 580 individuals placed by a German temporary work agency. The study aims to examine the linkages between human resource management practices and ambidexterity with regard to the integration of an external, highly qualified workforce into the firm. We focus on aspects of the internal labor market (ILM) and its relationship to concurrent firm exploration and exploitation. We argue that a dynamic ILM contributes to a firm’s capability for ambidexterity. Based on differences in the access to promotional opportunities of the ILM between temporary and permanent workers, we expect this contribution to be different for these groups of employees. We argue that whereas permanent employees receive job satisfaction from the opportunities of a dynamic ILM, temporary employees lack access to this source of job satisfaction and therefore do not contribute equally to organizational outcomes. Results of our study are intriguing since they do not support arguments on expected differences between these two types of workforce. Rather, findings confirm the importance of a dynamic ILM not only for permanent but also for temporary employees.     

Heuristic Coordination of Decentralized Inventory Systems Using Induced Backorder Costs

In this paper, we investigate a one‐warehouse multiple‐retailer system, where the inventory control decisions are coordinated using a near optimal induced backorder cost, β*. All installations use continuous review installation‐stock (R, Q) policies. The analysis builds on an approximation model where the stochastic warehouse delays are replaced by their correct averages. The contributions include insights as to how β* is influenced by system parameters, and the determination of simple closed form β* estimates. The latter offering a practical means to achieve coordinated control of large size systems.     

Job stress, social support, job satisfaction and absenteeism among offshore oil personnel

The major aim of this study was to examine how job stress in the offshore working environment may affect workers experience of strain. This study also analyses both the main and moderator effect of social support on the association between job stress and strain. The association between strain and absenteeism is also analysed. The analyses are based on a self-completion questionnaire survey among employees on offshore oil installations in the Norwegian part of the North Sea (n = 1137). The data collection was carried out in 1994. A similar study was conducted in 1990. Job stress was found to be associated with job dissatisfaction, as well as experience of strain. Social support from a supervisor had a main effect on strain. Some evidence of the moderating effects of social support were found. The employees who had been absent from work experienced most strain. It is concluded that job stress predicted job dissatisfaction and strain. In turn, strain and absenteeism were associated with each other. These results suggest that improving organizational and social factors should be the focal area in health promotion in the offshore oil industry.