Continuous Descent Operations Research Articles

A Decision Support Framework for Aircraft Arrival Scheduling and Trajectory Optimization in Terminal Maneuvering Areas

This study introduces a decision support framework that integrates aircraft trajectory optimization and arrival scheduling to facilitate efficient management of descent operations for arriving aircraft within terminal maneuvering areas. The framework comprises three modules designed to tackle specific challenges in the descent process. The first module formulates and solves a trajectory optimization problem, generating a range of candidate descent trajectories for each arriving aircraft. The options for descent operations include step-down descent operation, Continuous Descent Operation (CDO), and CDO with a lateral path stretching strategy. The second module addresses the assignment of conflict-free trajectories to aircraft, determining precise arrival times at each waypoint. This is achieved by solving an aircraft arrival scheduling problem. To overcome computational complexities, a novel variable neighborhood search algorithm is proposed as the solution approach. This algorithm utilizes three neighborhood structures within an extended relaxing and solving framework, and incorporates a tabu search algorithm to enhance the efficiency of the search process in the solution space. The third module focuses on comparing the total cost incurred from flight delays and fuel consumption across the three descent operations, enabling the selection of the most suitable operation for the descent process. The decision support framework is evaluated using real air traffic data from Guangzhou Baiyun International Airport. Experimental results demonstrate that the framework effectively supports air traffic controllers by scheduling more cost-efficient descent operations for arrival aircraft.

Environmental inefficiencies for arrival flights at European airports.

In this paper, we analyze two months of trajectory data for aircraft landing in five major European airports. Based on open ADS-B data from the OpenSky Network and open performance models, we enrich all trajectories with automatically detected procedure information, fuel consumption, and emissions for supported aircraft types. To assess the inefficiencies associated with holding patterns, point merges, and continuous descent operations across different airports, we propose methodologies to quantify and compare these environmental inefficiencies. Holding patterns are found to have a higher negative impact on the environment than point merge and continuous descent operations. Furthermore, the paper provides recommendations for procedure evaluations of future airports, which could help policymakers and relevant stakeholders to evaluate the environmental performances of arrival procedures based on open data and open models.

Digital Assistant for Arrival Scheduling with Conflict Prevention Capabilities

Nowadays, in view of the growing traffic volume, an appropriate aircraft sequencing in the arrival sector is needed to maintain safety levels and improve the performance of the runway system and flight times. This paper presents a digital assistant supporting the air traffic controller in aircraft sequencing by providing suggestions for next waypoints, speed adjustments and altitude holdings. On the one hand, the suggested paths are such to preserve safety by ensuring the prescribed minimum separation, while also promoting environmental benefits through continuous descent operations (CDO). On the other hand, the suggestions aim to reduce landing times, improving the runway throughput. The proposed tool exploits multipath planning, for which a global optimization technique is used in conjunction with the dynamic time warping distance metric and a reinforcement learning approach to resolve conflicts through speed modulation and/or altitude holding. The performances of the assistant are assessed by means of a multi-agent simulator tailoring its reasoning on the procedures of Olbia airport (Italy). The analysis of a stream of many random aircraft has revealed its effectiveness in terms of arrival time reduction against a standard first-come-first-served strategy, usually adopted by controllers, and strong conflict reduction while considering a CDO-like adherence. Additionally, the man/machine interaction is investigated through an analysis of the overall latency from the suggestions provided by the digital assistant up to the actual aircraft maneuvers.

Optimal aircraft arrival scheduling with continuous descent operations in busy terminal maneuvering areas

Continuous Descent Operation (CDO), an aircraft arrival procedure in which an aircraft descends from an optimal position with minimum engine thrust, can significantly reduce aircraft noise, fuel burn and emissions. The implementation of CDOs, however, requires more separation buffers among flights than traditional stepwise descents, resulting in loss of airspace and runway capacity. It is therefore challenging to maximize the number of aircraft performing CDOs for an airport, especially in busy terminal maneuvering areas. In this paper, we tackle the difficulty by developing an aircraft arrival scheduling model to sequence arrival aircraft before their merge point and generate conflict-free trajectories by means of a lateral path stretching method. The contributions of our study to the research community are twofold: firstly, we investigate a new aircraft arrival scheduling problem that incorporates both the CDO trajectory optimization and aircraft scheduling, and develop the first model simultaneously considering these two procedures; secondly, we conduct extensive computational experiments based on historical data in Guangzhou Baiyun International Airport, which would provide an important reference for future research in the area. Our numerical results demonstrate the benefit of the proposed CDO-based aircraft arrival scheduling approach in terms of reducing total flight time and saving fuel consumption when applied in this congested airport.

국내 표준계기도착절차(STAR)의 활용도 및 연속강하접근 운항 비율 분석

In response to the recent surge in aviation demand, major airport and aviation authorities continue to make efforts to formulate arrival procedures that take into account efficient aircraft separation, noise and environmental issues related to carbon (CO₂) emissions. In order to ensure efficient traffic control and environmental issues, as a result, a new concept Trombone, Point Merge, etc. have been introduced and widely used. However, these new concept incisions are becoming a factor that hinders operational efficiency and stability due to the restricted domestic airspace such as military airspace and excessive constraints of altitude, speed, etc. which do not reflect the concept of continuous descent operation and eventually needs to be modified to make continuous descent operation as feasible as possible. We herewith analyze and propose the way of improving flight safety and efficiency in the arrival operation procedure by supplementary modification which consequently contribute to the aviation industry international competitiveness.

Characterization of the terminal area of standard arrival routes using the queueing system

The article solves the problem of determining the probabilistic characteristics of the STARs legs which specify a sequencing technique of “point merge” and “trombone”-type considering the intensity of the air traffic flow and the formation of a queue. This task is closely related to the airspace efficiency, as well as to the limit values of flight safety performance. An application of the queueing system makes it possible to optimize the elements of the airspace structure on an objective basis, and in the event of considering the inverse problem to establish limit values for the air traffic flow characteristics. The characteristics of the “point merge” and “trombone”-type schemes become of prime importance in the air hub, where several airfields function of each other in a relatively small volume of airspace – as it happens in the Moscow air hub, so it is the given hub that is taken as a practical example. In this problem the basic model is the queueing system with limited-size queues where the optimal number of service channels in a stationary air traffic flow is determined in a probabilistic way. The stated model encapsulates the essence of the “trombone” or “point merge”-type scheme, where the number of service channels corresponds to the number of flight levels on the arc of the “point merge” or on the horizontal flight segment of the “trombone”. Now, the number of such flight levels, as a rule, corresponds to the number of standard arrival routes involved in the formation of a “trombone” (“point merge”), which, from a practical point of view, is excessive. The task of using the mathematical apparatus of the queueing system is to determine the optimal number of flight levels – service channels of the model while establishing the required probability of its failure. As a mathematical model of the queueing system, the “trombone”-type scheme is used, and in the mentioned above example, the structure of the airspace is presented using the “point merge”-type scheme as a regulator of the aircraft sequence for landing. All the computations are performed for the certain intensity of air traffic flow for a specified airfield, considering the full-scale application of continuous descent operations and continuous climb operations (CDO, CCO). As a result of solving the problem, the value for the optimal number of flight levels on the “trombone” or “point merge”-type scheme was obtained, and the dependence of the number of service channels (flight levels on the “trombone” or “point merge”) on the value of the given probability of the queueing system failure was shown. The proposed approach to the airspace structure formation has prospects for implementation.

A Path Stretching Model for Effective Terminal Airspace Management

This study presents a mathematical model to optimize the total fuel consumption per aircraft for the aircraft landing problem (ALP) using the path stretching (PS) method. The PS model applies vector maneuver (VM), speed reduction (SR), and flight path angle (FPA) change methods for aircraft operation. In addition, two different mixed-integer linear programming models utilizing the point merge system (PMS) are presented to compare the PS model as PMS is a widely used method in ALP. The first PMS model uses the VM to handle arrival traffic and solve aircraft conflicts. The second one implements the VM and the SR techniques. Furthermore, an exact solution algorithm is selected to obtain the optimal solution. The PS model aims to increase the number of continuous descent operations by eliminating the level flights. Two different linear regression equations are generated to calculate the fuel consumption and flight time values in descent operations considering realistic aircraft parameters, FPA, and average airspeed. The results demonstrate that the PS model can reduce the total fuel consumption per aircraft by 8.94% and 3.45% compared to the PMS models.

Sensitivity-Based Non-Linear Model Predictive Control for Aircraft Descent Operations Subject to Time Constraints

The ability to meet a controlled time of arrival while also flying a continuous descent operation will enable environmentally friendly and fuel efficient descent operations while simultaneously maintaining airport throughput. Previous work showed that model predictive control, a guidance strategy based on a reiterated update of the optimal trajectory during the descent, provides excellent environmental impact mitigation figures while meeting operational constraints in the presence of modeling errors. Despite that, the computational delay associated with the solution of the trajectory optimization problem could lead to performance degradation and stability issues. This paper proposes two guidance strategies based on the theory of neighboring extremals that alleviate this problem. Parametric sensitivities are obtained by linearization of the necessary conditions of optimality along the active optimal trajectory plan to rapidly update it for small perturbations, effectively converting the complex and time consuming non-linear programming problem into a manageable quadratic programming problem. Promising results, derived from more than 4000 simulations, show that the performance of this method is comparable to that of instantaneously recalculating the optimal trajectory at each time sample.

Automated sequencing and merging with dynamic aircraft arrival routes and speed management for continuous descent operations

In this paper, we present a novel methodology to manage arrival traffic in terminal airspace. We define two areas around the airport, aiming to efficiently schedule incoming traffic. A four-dimensional (4D) trajectory negotiation/synchronization process between the air traffic control officer (ATCO) and the aircraft is performed in the pre-sequencing area, while the aircraft are still in the en-route phase of flight. On the other hand, in the dynamic-trajectories area, the ATCO, with the help of a ground support tool, generates dynamic arrival routes that automatically adapt to the current traffic demand. These arrival routes allow the aircraft to fly neutral continuous descent operations (CDOs, descents with idle thrust and no speed-brakes usage) and to ensure a separation throughout the arrival procedure. We choose a mixed-integer-programming approach to generate the arrival routes, while we formulate and solve an optimal control problem to generate a set of candidate CDOs per aircraft. Results show that, with a sufficient look-ahead time, it is possible to assign a required time of arrival (RTA) within each aircraft-arrival time window that would allow to efficiently schedule traffic even in the most challenging and dense scenarios. Besides improving efficiency of current operations in terminal airspace, the methodology presented in this paper could become a technical enabler towards an extended arrival manager (E-AMAN) with extended capabilities and, ultimately, to a fully deployed trajectory based operations (TBO) environment.

Multi-Attributes Decision-Making for CDO Trajectory Planning in a Novel Terminal Airspace

Continuous Descent Operations (CDO) has been recognized as an effective way to significantly reduce fuel burn and noise impact. Designing efficient and flexible arrival routes for generating conflict-free and economical trajectories is a cornerstone for fully achieving CDO by high-level automation in high-density traffic scenarios. In this research, inspired by the Point Merge (PM), we design the Inverted Crown-Shaped Arrival Airspace (ICSAA) and its operational procedures to support Omni-directional CDO. In order to generate optimal conflict-free trajectories for upcoming aircraft in an efficient manner, we established a multi-objective trajectory optimization model solved by Non-dominated Sorting Genetic Algorithm with Elitist Strategy (NSGA-II). The Pareto solutions of minimal fuel consumption and trip time were achieved in single aircraft and highly complex multi-aircraft scenarios. Among all the elements of Pareto front, we obtained an unique solution with Entropy-Weights Method and TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) to strike a better trade-off among collision probability, fuel consumption, and trip time, which incorporates both air traffic controller’s and pilot’s interests. The effectiveness of CDO performance improvement and computational efficiency in different scenarios were verified. The ICSAA would be a promising structure that promotes the application of automated and flexible CDO.

Flight analyses for realization of Continuous Descent Operation in the congested airspace

Flight analyses for realization of Continuous Descent Operation in the congested airspace

Traffic synchronization in terminal airspace to enable continuous descent operations in trombone sequencing and merging procedures: An implementation study for Frankfurt airport

This paper proposes to enhance the current tromboning paradigm with a four dimensional trajectory negotiation and synchronization process with the aim to maximise the number of neutral Continuous descent operations (CDOs, descents with idle thrust and no speed-brakes usage) achieved by the arriving traffic in terminal maneuvering areas (TMAs). An optimal control problem has been formulated and solved in order to generate a set of candidate CDO trajectories per aircraft, while a mixed-integer-linear programming model has been built in order to optimally assign routes of the arrival procedure and required times of arrival (RTAs) to the arriving traffic when still in cruise. The assessment has been performed for Frankfurt am Main airport (Germany), by using arrival traffic gathered from historical data. Results show that, after assigning an RTA and a route to every arriving aircraft, it is possible to maximize the number of aircraft performing CDOs while ensuring a safe time separation throughout the arrival procedure. For low traffic scenarios, the totality of traffic can be successfully scheduled, while for high traffic scenarios this is not the case and not all aircraft can be scheduled if neutral CDOs are flown. However, by assuming different arbitrarily defined arrival times to the TMA or by considering more additional shortcuts in the trombone procedure it is possible to increase the number of aircraft scheduled. Besides improving current operations in the short-mid term, the methodology presented in this paper could become a technical enabler towards a fully deployed trajectory based operations (TBO) environment.

Feasibility study on applying continuous descent operations in congested airspace with speed control functionality: Fixed flight-path angle descent

Continuous descent operations (CDO) are an efficient descent operation for passenger/cargo aircraft and implemented at various airports worldwide. However, it is difficult for air traffic controller (ATCo) to predict the CDO trajectory and control the CDO aircraft, therefore limiting the applicable window only during the low traffic periods. To maximize potential benefits by introducing the CDO, it is required to implement the CDO into congested airspace and time window. This study introduces an augmentation to CDO application in the congested airspace, called fixed flight-path angle (Fixed-FPA) descent. The fixed-FPA descent was originally proposed and investigated only for small passenger jet aircraft; thereafter the fixed-FPA descent was introduced to large passenger jet aircraft. This proposed procedure consists of several altitude restrictions along the arrival route. By following the altitude restrictions, the aircraft flies with a specified flight-path angle. Additionally, specifying the flight-path angle facilitates the prediction of the CDO trajectory by ATCo. Moreover, by setting a shallower flight-path angle compared with the conventional CDO, the fixed-FPA descent is capable of speed control. The preceding studies conducted only the preliminary feasibility study of the fixed-FPA descent on large jet aircraft. In this study, a series of full-flight simulator experiments and Monte Carlo simulations were conducted to assess the operational feasibility and demonstrate the capabilities of fixed-FPA descent. Experimental results demonstrated that the fixed-FPA descent meets the requirements for integrating the CDO into congested airspace, such that the vertical path of the CDO can be predicted by the ATCo, and the speed of the CDO aircraft is controllable. Additionally, the simulation results revealed that the fixed-FPA descent has better fuel efficiency than the conventional when the descending aircraft is required to delay its arrival time.

Automation for Separation with Continuous Descent Operations: Dynamic Aircraft Arrival Routes

This paper presents a mixed-integer programming approach to compute aircraft arrival routes in a terminal maneuvering area (TMA) with guaranteed temporal separation of all aircraft arriving within a given time period. Furthermore, the aircraft are assumed to be flying according to their optimal continous descent operation speed profile with idle thrust and no speed brakes usage. The arrival routes form a merge tree that satisfies several operational constraints; for example, all merge points are spatially separated. How the continuous descent operation speed profiles for different route lengths are computed is detailed. Experimental results are presented for calculation of fully automated continuous descent operation-enabled arrival routes during 1 h of operation on a busy day at a Stockholm terminal maneuvering area. The current framework successfully generates an arrival tree, merging the traffic from all TMA entry points to the runway for 30 min intervals. For a complete 1 h period, two trees (per 30 min) are computed that differ as little as possible.

Using Broadcast Wind Observations to Update the Optimal Descent Trajectory in Real-Time

The ability to meet a controlled time of arrival during a continuous descent operation will enable environmentally friendly and fuel-efficient descent operations while simultaneously maintaining airport throughput. However, if the wind forecast used to compute the initial trajectory plan is not accurate enough, the guidance system will need to correct time deviations from the plan during the execution of the descent. Previous work proposed an onboard guidance strategy based on model predictive control, which repeatedly updates the trajectory plan in real-time from the current aircraft state and for the remainder of the descent. However, the wind conditions downstream, at altitudes not explored yet, were difficult to predict due to the lack of data. This paper shows the potential benefits of using wind observations, broadcast by nearby aircraft, to reconstruct the wind profile downstream. The wind profile in the trajectory optimization problem is modeled as a spline, control points of which are updated to fit the observations before replanning the trajectory. Results from simulations using realistic wind data show that the performance of model predictive control significantly improves when including up-to-date wind observations, in terms of time and energy errors at the metering fix and fuel consumption.

Design Factors of Guiding Aircraft Through Continuous Descent Operations: Pilot and Controller Perspectives

ABSTRACTObjective: This survey identifies the design factors needed to guide aircraft through continuous descent operation (CDO) procedures.Background: Three possible alternatives for CDO at Taoyuan International Airport (TPE) in Taiwan are presented: (a) open path-radar vectoring-based CDO, (b) open path-time control-based CDO, and (c) open path procedure permitting CDO to downwind.Method: One hundred and twenty surveys were distributed and 61 pilots and 49 controllers responded. Eight pilots and 25 controllers had experience implementing CDOs.Results: All respondents ranked altitude control as the most important design factor. Pilots with CDO experience preferred to reduce the frequency of communication in the procedure, whereas experienced controllers expected to know the approach path as early as possible.Conclusion: Altitude control is the highest priority design factor for improving the current CDO procedure at TPE.

Workload Perception of Air Traffic Control Officers and Pilots During Continuous Descent Operations Approach Procedures

Abstract. The paper examines the workload perceived by air traffic control officers (ATCOs) and pilots during continuous descent operations (CDOs), applying closed- and open-path procedures. CDOs reduce fuel consumption and noise emissions. Therefore, they are supported by airports as well as airlines. However, their use often depends on pilots asking for CDOs and controllers giving approval and directions. An adapted NASA Total Load Index (TLX) was used to measure the workload perception of ATCOs and pilots when applying CDOs at selected European airports. The main finding is that ATCOs’ workload increased when giving both closed- and open-path CDOs, which may have a negative impact on their willingness to apply CDOs. The main problem reported by pilots was insufficient distance-to-go information provided by ATCOs. The workload change is important when considering the use of CDOs.

Integration of the ground-based augmentation system in continuous descent operations

Predictability is a necessity in today's commercial flight operations if delays are to be minimized. Possible mitigations, such as the implementation of continuous descent arrivals (CDAs), may help generate the required procedural predictability to curtail these delays. However, on the basis of its individual avionics suite, each aircraft follows a different barometric vertical descent path; furthermore, the aircraft may be given additional level-off segments by air traffic control to compensate for possible deviations in the vertical profile. Therefore, aircraft flying the current descent profiles are too unpredictable and thus the procedures cannot be implemented in complex airspace structures or when traffic is moderate to high. This study introduces a mitigation to this problem by taking the global positioning system (GPS) one step further by integrating the GPS-based ground-based augmentation system (GBAS) into the new optimized continuous decent arrival procedure, subsequently, allowing for the introduction of a geometrical vertical guidance, namely, the GBASCDA, which will make the aircraft flying the descent profile predictable. With the increase in availability of GBAS aircraft equipage, specifically the GPS landing system (GLS), and the approaching amendment of the Appendix E of the Minimum Operational Performance Standards for GPS Local Area Augmentation System Airborne Equipment–RTCA DO-253D, this idea of the integration of the GBAS on the arrival/descent segment as a viable solution may be finally coming within reach.

Fuel-Efficient Trajectories Traffic Synchronization

Continuous descent operations (CDOs) with required times of arrival (RTA) have been identified as a potential solution for reducing the environmental footprint of aviation in the terminal maneuvering area without compromising capacity. This paper assesses the feasibility of replacing current air traffic control sequencing and merging techniques, mainly based on path stretching and air holding, by a control based on RTA over metering fixes on known and fixed arrival routes. Because the remaining distance to the runway threshold is always known by the aircraft crew, this would allow engine-idle CDOs that do not require speed-brake usage and where only elevator control is used to meet the RTA. The assessment has been performed for Barcelona-El Prat Airport (Spain) using historical traffic demand data. The earliest and latest trajectories at a metering fix for each inbound aircraft were computed assuming engine-idle CDOs. Given the attainable RTA window for each aircraft, the aircraft sequencing problem was solved. The results show that assigning RTA allows optimizing the landing sequence when air traffic is low. For scenarios with high-traffic loads and late RTA assignments, path stretching still was found to be necessary. The minimum distance from the runway where inbound aircraft should receive the RTA to fully remove any radar vectoring was also analyzed. It was demonstrated that the assignment of RTA well before starting the descent would favor to enable full CDOs.

Study of Point Merge technique for efficient Continuous Descent Operations in TMA

This paper provides a study addressing a methodology for the automatic generation of efficient Curved and Continuous Descent Approach (CCDA) trajectories, supported by arrival flows merging techniques, in a typical TMA, to reduce fuel consumption as well as environmental emissions. The proposed methodology has been applied, through numerical simulations, to an Italian airport, resulting in a considerable fuel saving (up to 30%) with respect to conventional standard arrival routes.