Wake Vortex Encounter Risk Assessment for Crosswind Departures

In the European research project, CREDOS (Crosswind-Reduced Separations for Departure Operations), the feasibility of a concept for reduced wake turbulence separations upon departure in crosswind conditions has been investigated. The safety assessment of this concept includes risk assessment with respect to wake vortex encounters. This paper describes the methodology developed for this assessment and its application during the project. The methodology employs two simulation tools, the Wake Vortex Scenarios Simulation Package for Departure (Wake Scene-D) and the Vortex Encounter Severity Assessment for Departure (VESA-D), which are extensions of existing tools related to the departure flight phase. WakeScene-D primarily determines the frequency of wake encounters, whereas VESA-D estimates the severity of these encounters. Both can be combined to quantify and compare wake encounter risk for various departure scenarios. In the risk assessment, departures with variable aircraft separations and varying crosswind conditions were investigated to determine which crosswind level is necessary to suspend wake-turbulence-related separations during departure without degrading safety. Monte Carlo simulations have been conducted comparing medium and heavy aircraft type departures with 2 mm. of separation to departures with a separation of 1 min. under varying crosswind strengths. The results not only give an indication of which crosswind magnitudes could be sufficient to safely suspend wake-turbulence-related separations upon takeoff, but they also reveal significant influences, such as the departure route layout and the change of wind direction with altitude, on wake encounter risk.