Assessment of Wake-Vortex Encounter Probabilities for Crosswind Departure Scenarios

A IRCRAFT-GENERATEDwakevortices pose a potential risk to following aircraft in various flight phases, whereas most wakevortex encounters are reported for approach and landing and for takeoff and climb [1]. The International Civil Aviation Organization (ICAO) wake-vortex aircraft separation standards [2] established in the 1970s increasingly degrade aviation efficiency when traffic congestion limits airport capacity during landing and takeoff. Research has shown that the transport and persistence of wake vortices are highly dependent on meteorological conditions [3,4], so that in many cases the separation standards are overconservative. For single-runway operations, analyses [5–7] suggest that, above a certain crosswind threshold, vortices are blown out of the flight corridor and pose no further threat to following aircraft. The European Union (EU) project CREDOS (CrosswindReduced Separations for Departure Operations) intends to demonstrate the operational feasibility of a concept of operations that uses measures of the prevailing crosswind component to allow temporary suspension of the need to applywake turbulence separations between successive departing aircraft. The focus on the combination of crosswind and departures has significant advantages: The follower aircraft is still on the ground when the controller schedules the separation. So the controller always has the possibility to extend the separation without requiring the pilot to make a maneuver. This beneficial situation also reduces the time horizon for which crosswind conditions must be anticipated. Second, in contrast to arrival situations the leader aircraft is generally faster so that the actual separations tend to increase. WakeScene-D (Wake Vortex Scenarios Simulation Package for Departure) [8] is an extension of WakeScene, which was developed for approach and landing and is described in detail in [9]. WakeScene-D estimates the probability to encounter wake vortices in different traffic and crosswind scenarios using Monte Carlo simulation in a domain ranging from the runway to an altitude of 3000 ft above ground. In cases with potential wake encounters all relevant parameters can be provided to VESA (Vortex Encounter Severity Assessment) [10,11], a tool developed by Airbus, which may subsequently perform detailed investigations of the severity of the encounter. WakeScene-D consists of elements that model traffic mix, aircraft trajectories, meteorological conditions, wake-vortex evolution, and potential hazard area. The process and data flows are controlled and evaluated by the MATLAB-based environment MOPS (Multi-Objective Parameter Synthesis) [12]. Within CREDOSWakeScene-D is used to support the definition of suitable crosswind criteria that allow reducing aircraft separations, to identify the sensitivity and interplay of the employed submodels and parameter combinations, and to support risk analyses taking into account a broad range of variables that determine the probability and risk of a wake-vortex encounter. Related models have been developed for approach and landing: 1) WAVIR (wake-vortex-induced risk) [13] is capable of estimating frequencies of certain risk events in a given scenario. 2) ASAT (Airspace Simulation and Analysis for TERPS, where TERPS stands for Terminal Instrument Procedures) is a multifaceted computer tool for aviation-related simulations and safety evaluations that has not been specifically designed as a wake-vortex riskassessment model. Similar to WakeScene, ASAT has an interface to VESA that permits subsequent wake-vortex encounter severity assessment. 3) The Vortex Risk Analysis Tool has been employed for the risk assessment of the High Approach Landing System/Dual-Threshold Operation (HALS/DTOP) implemented at Frankfurt airport. HALS/ DTOP aims at increasing the capacity of the closely spaced parallel runway system by employing a second threshold displaced by 1500 m for the southern runway. 4) A comprehensive air traffic control wake-vortex safety and capacity-integrated platform has also been generated in the EU project ATC-Wake [14]. Reference [1] provides a comprehensive survey on operational concepts designated to increase airport capacity and the regulatory framework, which is relevant for the associated risk assessments as well as many other wake-vortex-related issues. First, this paper briefly describes the operating sequence of WakeScene-D and the employed submodels. For a detailed description of WakeScene-D, including statements of the validation work performed for the submodels and databases we refer to [8]. Received23December 2009; revision received 4March 2010; accepted for publication 4 May 2010. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0021-8669/11 and $10.00 in correspondence with the CCC. ∗Research Scientist, Institute of Atmospheric Physics; frank. [email protected]. Institute of Robotics and Mechatronics. Data available online at www.eurocontrol.int/eec/credos/ retrieved [25 March 2011]. JOURNAL OF AIRCRAFT Vol. 48, No. 3, May–June 2011