Engineering Notes ENGINEERING NOTES are short manuscripts describing new developments or important results of a preliminary nature. These Notes should not exceed 2500 words (where a figure or table counts as 200 words). Following informal review by the Editors, they may be published within a few months of the date of receipt. Style requirements are the same as for regular contributions (see inside back cover).

The WakeScene-D (Wake Vortex Scenarios Simulation Package for Departure) software package has been developed for comprehensive airspace simulations of takeoff and departure. WakeScene-D consists of modules that model traffic mix, aircraft trajectories, meteorological conditions, wake-vortex evolution, and potential hazard area. The software package 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. A comparison with measured vortex tracks of about 10,000 departures from runway 25R of Frankfurt airport indicates good agreement of global wake-vortex transport characteristics in ground proximity. The standard departure situation employing a 2 min aircraft separation is compared with scenarios with reduced departure separations and various crosswind conditions. Comprehensive sensitivity analyses have been conducted that are briefly recapitulated. Effects related to departure-route combinations and wind-direction sectors are reported in more detail. Finally, an advanced scenario with an asymmetric crosswind criterion is introduced.

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 (WakeScene-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 min. 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.

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Ground Based Augmentation Systems (GBAS) for the precision approach of aircraft have never been so close to support automatic approach and landings under CAT IIIc conditions as they are today. However, as one key requirement for certification, it has to be demonstrated that the required integrity, continuity and availability allocations for GBAS are met, even under the most unfavorable circumstances. As for ILS/MLS, the performance of the total system (GBAS, the aircraft and its automatic landing system) is the key to eventual certification. Contrary to ILS/MLS-based guidance, at this moment no standard models and parameters for navigation errors and disturbances have been defined yet for assessing automatic landing performance based on GBAS. This raises the questions (1) how well does the integrated system perform with state of the art GBAS error models, and (2) for a given performance level reached with ILS/MLS, how much error could be tolerated when using GBAS instead? In this paper we have made a preliminary step to find an answer to the first question. To this end we have taken an existing, flight tested automatic landing system, tuned for use with DLRs fly-by-wire test bed ATTAS (Advanced Technologies Testing Aircraft System), which is representative for EASA Part 25-class aircraft. The landing system was adapted for use with GBAS and an advanced GBAS error model was incorporated in the simulation model. With this set-up, we performed the same Monte-Carlo simulations as were originally done with ILS. Initial results indicate that, based in the adopted error models, CS-AWO criteria can be met with more ease than with ILS/MLS-based guidance. It is expected that performance of GBAS-autoland systems can be further improved by exploiting new features that GBAS has on offer, tolerating larger NSE errors or possibly allowing operational autoland limitations, like maximum crosswind, to be relaxed 978-1-4244-5037-4/10/$26.00 ©2010 IEEE