Wake Vortex Separation Research Articles

Assessment of dynamic pairwise wake vortex separations for approach and landing at Vienna airport

The Wake Vortex Prediction System WSVS (WirbelSchleppenVorhersageSystem) has been developed to tactically increase airport capacity by employing dynamically adjusted aircraft separations for approach and landing without compromising safety. For this purpose, the WSVS considers the involved aircraft type pairing, the prevailing weather conditions, and the resulting wake vortex behavior. A Monte Carlo simulation study demonstrates that the WSVS is well adjusted to a reasonable level of safety. The simulation study evaluates the probability that wake vortices still linger within defined radii around the follower aircraft and compares this probability to measurement data collected at five major international airports. The potential of the WSVS to optimize aircraft separations is assessed by employing twelve months of traffic and weather prediction data collected at Vienna International Airport. Analyses of the separation reduction potential are established and compared to current regulations. Dependencies on prevailing headwind and crosswind conditions are discussed in terms of individual wake vortex behavior and statistical distributions of wake turbulence separations. The results indicate that substantial potential for safely reduced aircraft separations exists mainly under sufficiently strong crosswind conditions for any aircraft type combination requiring wake vortex separation minima.

Simulation of Runway Operations with Application of Dynamic Wake Separations to Study Runway Limitations

This paper presents an evaluation of runway operations at Chicago O’Hare International Airport to estimate the impact of proposed wake vortex separation including Recategorization Phase II and III dynamic separations. The evaluation uses a Monte Carlo simulation model that considers arrival and departure operations. The simulation accounts for static and dynamic wake vortex separations, aircraft fleet mix, runway occupancy times, aircraft approach speeds, aircraft wake circulation capacity, environmental conditions, and operational error buffers. Airport data considered for this analysis are based on Airport Surface Detection Equipment Model X records from Chicago O’Hare International Airport from January to November 2016. Dynamic wake separations are tailored to each unique set of conditions by using environmental and aircraft performance parameters as input and allowing aircraft to be exposed to the same wake vortex strength as in Recategorization Phase II (RECAT II). The analysis shows that further reductions beyond RECAT II for aircraft pairs separated by 2 nautical miles or less is not operationally feasible. These wake separations already result in little to no wake dependency. When this is the case, the challenges in wake separation are to meet runway occupancy times and to make sure aircraft separations allow for human operational variations without resulting in aircraft turnarounds or double-aircraft-occupancy runway violations.

Improving aircraft approach operations taking into account noise and fuel consumption

While air transport brings very significant economic and social benefits to the cities and regions served by airports, aircraft noise is the single major cause of community opposition to airport operations, becoming a critical issue that affects the sustainability of future traffic growth. However, planning operations exclusively focusing on noise impact may result in an increase of fuel consumption or delays. This paper develops a suitable bi-objective model for landing aircraft, which finds a schedule that minimises noise impact, total fuel consumption and delays, under wake vortex separation and Constrained Position Shifting restrictions. The results of this model are compared with real operations in a major European airport to assess the potential level of improvements. By comparing with real data from Madrid-Barajas airport, the research shows potential improvements of up to 4.5% reduction of total fuel consumption (without increasing noise levels) only by modifying the sequence of arrivals, and up to 43% (without extra fuel consumption) of reduction in noise impact over the populations under study.

Minimizing deviation from scheduled times in a single mixed-operation runway

The dynamic nature of airports demands the development of scheduling algorithms that are computationally efficient and therefore amenable to replanning when new traffic events occur. The main objective of this research is to design an algorithm with very low computational times able to minimize delays in the scheduled times of arrival and departure flights in an airport with a mixed-operation runway, under wake vortex separation and Constrained Position Shifting restrictions. The simulated annealing algorithm obtains a 95% improvement on time delays in less than one second of computation for the test instances generated, which means that it can be used online for high-demand scenarios to reduce delays. It has also been tested in a public testbed as well as in a real environment, showing an improvement of 30% in the time delays of real operations at London Gatwick airport.

On an analytical model of wake vortex separation of aircraft

ABSTRACTA theory is presented on the effect of wake turbulence of a leading aircraft on the roll stability of a following aircraft, leading to a simple formula for the safe separation distance between the two aircraft that provides estimates of aircraft separation distances comparable to existing empirical regulations, based on experience. The formula includes the effects of flight and atmospheric conditions, and the characteristics of the leading and following aircraft; it applies to similar or dissimilar aircraft, and it indicates the parameters and conditions leading to increasing or decreasing separation. The formula is applied not only to the three International Civil Aviation Organization (ICAO) categories of aircraft (light, medium and heavy, respectively, Cessna Citation, B737 and B747) but also to ‘special’ aircraft requiring larger separation distance (Boeing 757) and to the world’s largest airliner (Airbus A380).

Radar wake‐vortices cross‐section/Doppler signature characterisation based on simulation and field tests trials

Runway operation is the limiting factor for the overall throughput of airports. Today the International Civil Aviation Organization (ICAO) imposes wake vortex separation minima between following aircrafts that are based on simple pair-wise rules. However, the lifetime of wake vortices results from a much broader basis of factors, that ranges from a large set of aircraft parameters to meteorological conditions and traffic mix. In particular atmospheric conditions can significantly reduce wake hazard, for instance, in case of strong turbulence or crosswinds. While such situations could allow a reduction of the separation minima, safety reasons and the current technical challenges of detecting and managing such scenarios leads to the strict application of the ICAO standards. With the aid of accurate wind data and precise measurements of wake vortices, more efficient intervals could be set, particularly when weather conditions turn favourable. Depending on traffic intensity, these adjustments could enhance airport capacity, and generate major commercial benefits. This study deals with recent development in the radar technology to attain such goals. It presents (i) the trials of an electronic scanning radar to be used in a future wake turbulence advisory system and (ii) theoretical and numerical analysis of the radar response in clear air and in rainy weather. Part of this work has been achieved with the support of the European ATM research program SESAR.

飞行器尾涡对的不稳定性建模

For aircrafts the wake vortex separation and the disturbance-induced vortex instability draw more and more concerns. A 1st-order approximation of the Biot-Savart law was used to build the induced motion model for arbitrarily multiple vortex pairs. Symmetric and antisymmetric modes of the induced motion of vortex pairs were deduced with the linear combination method. The properties of the modal matrix eigenvalues were obtained to describe instability of the multiple vortex pairs. The modes of 2 vortex pairs were used for validation of the proposed model, which was thereafter extended to 3 vortex pairs to give the instable modes corresponding to the modal matrices. The theoretical analysis and eigenvalue calculation show that, with the increase of the number of vortex filaments, the instability of the 3 vortex pairs will rise, and the amplification effects of the vortex system on the disturbance will highten.

An Improved MPS Algorithm for Optimal Scheduling of Aircraft Arrivals at Congested Airports

This paper presents an improved aircraft arrival sequencing and scheduling model, and designs a new efficient algorithm to optimize the arrival traffic flow at the Terminal Radar Approach Control (TRACON) area. It has three steps: Firstly the aircrafts in same route are united into groups, then the positionmatrix is created according to a series of ATC (Air Traffic Control) constraints, finally the solution space tree is built to search the optimal sequence. The algorithm also take into account Max Position Shift (MPS) and wake vortex separations. Finally the algorithm is validated with practical data, the results shows the computing scale is small and the proportion of continuous landing aircrafts in final sequence is more in contrast to other algorithms, it is more convenient for the operation of controllers.

Optimal scheduling for aircraft departures

In this work we introduce a mathematical model to improve the aircraft departures planning system. The objective is to maximize the airport performances, minimize delays in the runway operations and to support the air controller work. The followed approach is based on the combination of a single runway two stages algorithm with a multi-runway procedure to find the better departures scheduling. By means of the two stages algorithm, a complex problem dealing with multi-objective functions is split into two inter-connected one dimensional problems. In the first stage the aim is to minimize the throughput, defined as the number of aircraft in the time unit, subject to wake vortex separations constraint. An "ad hoc" control heuristic method is used to mix the pre-fixed landing arrivals slots with the departure ones outgoing from the first stage. In the second stage the class sequence, generated by the first stage, is computed in order to minimize the delays between the actual and estimated take-off time of each departing aircraft, subject to fixed calculated take off time and estimated take off times, and considering some possible departing priority. Then a multi-runway procedure is introduced, consisting of an heuristic methodology, which uses the two stage algorithm, to locate as better as possible the aircraft on each available runway. The result is the better feasible take-off sequence in a referred time window. Some simulations on typical flight strips from Milano Malpensa airport in Italy, having two runways, are shown.

Effect of Turbulence Model on Simulation of Vehicle Aerodynamic Characteristics Based on XFlow

The stability, comfort and safety of vehicles depend largely on the aerodynamic characteristics of the vehicle in high speed. As the turbulence model plays a decisive factor in the numerical simulation of aerodynamic characteristics, a simulation analysis of Ahmed model with a slant angle of is carried out by the XFlow software. Then the paper presents the changes of aerodynamic parameters relative to the experimental values with four turbulence models: Spalart-Allmaras model, WALE model, Dynamic Smagorinsky model and Smagorinsky model. It is found that the result of simulation with Smagorinsky model is in good agreement with experimental value, and the simulation of the wake vortex separation is consistent with the actual phenomenon. The Smagorinsky turbulence model has a good simulation precision.

Integrating Unmanned Aircraft Efficiently into Hub Airport Approach Procedures

Currently, most civil and military UAS operations are taking place in segregated airspace so that collision avoidance and separation with other traffic is of minor concern. To further enable the UAS operational scope, Unmanned Aircraft (UA) must be able to fly in airspace where other traffic is operating as well. This becomes increasingly important when considering the effects on efficiency and safety caused by the participation of UAS in the approaching and departing traffic at (civil) hub airports. Enabling a smooth integration of UA into the traffic stream of an airport requires the examination of two different aspects. One important aspect is the handling of UA Beyond Visual Line Of Sight (BVLOS) under the requirement of wake vortex separation and a sustained Air Traffic Control (ATC) communication. A second aspect that needs to be considered is the potential of improving current UAS approach procedures and their effect on airport capacity. In this paper, a concept is presented, in which a single generic Ground Control Station (GCS), located at or near the airport can be used to control multiple UAS and, in conjunction with advanced GBAS approach procedures, can facilitate the shared use of an airport.

Towards wake vortex safety and capacity increase: the integrated fusion approach and its demands on prediction models and detection sensors

Wake vortices and the prevention of wake vortex encounters are both an issue of safety and capacity in today’s air transportation system. Current wake vortex separations are safe but also very conservative and thus have an adverse effect on capacity of airports. This article deals with the concept of fused wake vortex prediction and detection with the objective to deliver wake vortex strength and position with a high level of accuracy and reliability. The collaboration approach aims at fusion of models and sensors available for forecast and detection of hazardous wake turbulence in order to improve the overall system performance using the complementary capabilities of the single components. Different methods of coupling models with measurements are introduced and resulting the aspect of requirements for the prediction model and measurement sensor is presented. The implementation of an error-state system is presented and compared to sole prediction and sole sensor results. The results indicate that the fusion approach delivers benefits like reduced uncertainty of prediction and increased availability of detection and thus has the ability to increase airport and air space capacity while maintaining or even improving current wake vortex safety.

The Study of Reducing the Take-Off Congestion

The problem of Take-Off congestion is studied, and then a new concept is proposed that the double direction Take-Off (DDT) can be adopted in the mode of time division alternatively on ordinary runway to solve the problem effectively. This mode does not violate the runway occupation rule which limits the only one aircraft on the runway at the same time for safety. The wake vortex separation limit is kept also. It will reduce the occupation time and the Take-Off and landing length wasted on runway. The relationship between the rolling distance and the wind speed is considered in relation to the runway length permission. This will lead to significant increase on effectiveness and utility of runway, equally on economic enhancement for aircrafts, airlines and airports.

The Wake Vortex Prediction and Monitoring System WSVBS Part I: Design

The design of the Wake Vortex Prediction and Monitoring System WSVBS is described with all its components and their interaction. The WSVBS was developed to tactically increase airport capacity for approach and landing on closely-spaced parallel runways. The WSVBS supports dynamic adjustment of aircraft wake vortex separations dependent on weather conditions and the resulting wake vortex behavior without compromising safety. Dedicated meteorological instrumentation and short-term numerical terminal weather prediction provide the input to the prediction of wake-vortex behavior and respective safety areas. The prediction tools employ a number of conservative aircraft parameter combinations that represent the medium and heavy aircraft weight categories. Safe aircraft separations correspond to times when the predicted safety areas associated with wake vortices generated by leading heavy aircraft cannot overlap the arrival flight corridor. A LIDAR monitors the correctness of WSVBS predictions in the most critical regions at low altitude.

The Wake Vortex Prediction and Monitoring System WSVBS Part II: Performance and ATC Integration at Frankfurt Airport

The performance and the ATC test integration of DLR’s wake vortex advisory system, WSVBS, for the dependent parallel runways 25L and 25R at Frankfurt Airport are described. WSVBS has components to forecast and monitor the local weather and to predict and monitor wake transport and decay along the glide paths. Integration with the DLR’s arrival manager AMAN has also been demonstrated. Every 10 minutes the WSVBS delivers minimum safe aircraft separation times for the next hour, which are translated into operational modes for runways 25L/R aiming at tactically improving capacity to reduce delays. During a performance test described herein the system was stable and the predicted minimum separation times were confirmed by measurements. Capacity-improving wake-vortex separation concepts of operation could have been used in 75% of the time and continuously applied for at least several tens of minutes. From fast-time simulations the (strategic) capacity gain for Frankfurt was estimated to be 3%, taking into account the real traffic mix and operational constraints.

Runway occupancy time as element of runway capacity

A great many factors determine airside capacity. In the firstgroup are those factors correlated with characteristics of manoeuvringarea such as number, layout and location of runwaysand taxiways. In the following group there are elements correlatedwith flight operations such as arrival, departure, touchand go operations and also the factors related to the aircraftsuch as weight, separation and wake vortex separation criteria.In the last group there are all other elements such as meteorologicalconditions and restrictions, ecological conditions, airtraffic control skills and equipment, etc.This paper presents a detailed description of runway occupancytime in arriving and departing flight operations and indicationsfor possible improvements

Full-flight simulator study for wake vortex hazard area investigation

Simplified hazard areas (SHA) can help to overcome the wake vortex problem. Avoiding these zones allows safe and undisturbed flight operations. The definition of the hazard areas is based on the nominal required roll control power. The nominal limit for this value must be chosen carefully to ensure that outside the hazard area all wake vortex effects are noncritical. For the determination of such a limit offline simulations and full flight simulator studies were conducted. For a given roll control limit the hazard area dimensions are established with the “simplified hazard area prediction” method (SHAPe). Parameterization of the input parameters makes this method universally applicable to different aircraft types. SHAPe represents an essential element of the wake vortex prediction and observation system within the DLR project Wirbelschleppe II, for the generation of safe dynamic wake vortex separations.

The Development of the Wake Vortices Warning System for Frankfurt Airport: Theory and Implementation

A Wake Vortices Warning System (WVWS) has been identified as a candidate means for increasing the capacity of Frankfurt Airport. For certain meteorological conditions, the WVWS is expected to allow for the suspension of required wake vortex separations between aircraft approaching the airport’s two parallel runways 25L and 25R. At present, the proximity of these parallel runways does not allow wake-vortex-independent operations as a standard procedure. The task of the WVWS is to model the propagation of wake vortices produced in the atmospheric boundary layer by aircraft approaching the runways, and to forecast the wake vortex transport, which is influenced mainly by the crosswind. This predicted propagation of the wake vortices is used to determine the risk for approaching aircraft that is produced by wake vortices generated in the vicinity of the two runways. On the basis of this hazard prediction, an appropriate landing/operational procedure is recommended to the controller.The development of the WVWS is based on the results of a long-term research program started in the 1980s. This program included an extensive measurement campaign at Frankfurt Airport and thorough analysis of the operational implications of a WVWS. The development of the basic algorithms for the WVWS prototype began in 1992. A project with the objective of implementing, installing, and evaluating a WVWS system at Frankfurt Airport was started in March 1995. The system integration was completed in the summer of 1996. Evaluation of the system is still in progress.The WVWS project at Frankfurt Airport will be reviewed in two papers. This paper presents the project history, the basic theory and algorithms of the WVWS, the landing procedures for operational use of the system, the WVWS design and implementation, and the testing and evaluation of the system. A future paper will present the methods used for risk analysis, costbenefit analysis, and the results obtained.

Wake-vortex separation distances when flight-path corridors are constrained

Since the vortex wakes of large transport aircraft can pose a hazard to smaller following aircraft during landing and takeoff operations, certain separation guidelines are followed while aircraft are in the approach and departure corridors at airports. These guidelines reduce the capacity of airports because the separation distances are larger than other airport factors require. This paper studies the effect that a decrease in the size of the cross-section of the flight corridors for air traffic control would have on the wake-vortex separation guidelines; e.g., when the Global Positioning System (GPS) is implemented for air traffic control. It is first shown why smaller flight corridors permit reduced spacings at airports. Several arrangements of smaller flight corridors are then presented to illustrate how differing atmospheric and airport conditions can be accommodated. These considerations indicate that a reduction is then permissible in the wake-vortex spacings while still retaining the same or an improved degree of safety.