Guidelines for Avoiding Vortex Wakes During Use of Closely-Spaced Parallel Runways

Abstract

This paper proposes a reliable method for estimation of the movement and spread of lift-generated vortex wakes as a function of time to better enable aircraft arriving at airports to avoid the hazards associated with the wakes of preceding aircraft. Operations on closely-spaced parallel runways illustrate how the method may be applied. An overview presents the aerodynamic mechanisms that cause the hazardous parts of lift-generated wakes to spread as a function of time. A computational method developed for determination of the spread of vortex wakes as a function of time is then applied to operations of aircraft as they approach closely-spaced parallel runways. The results suggest guidelines for efficiently and effectively avoiding the vortex wakes of preceding aircraft. Because the theoretical tools developed and the measurements of the components of the time-averaged wind and its gust magnitudes contain uncertainties, flight tests are recommended to confirm and to refine the guidelines presented, and to verify the techniques used to measure the atmospheric parameters that control wake intrusion.

Interaction of Aircraft Wakes From Laterally Spaced Aircraft

“…3,7,8 A concept by Rossow 9,10 proposes precision approaches that follow individual compact flight corridors. In this concept, a wake-zone fast-time model 11 is used to manage the wake vortex risk, 12 and the corridors are navigated with systems that utilize global positioning satellites (GPS). Rossow's concept also allows for new runways to be paved between existing ones, thus further improving capacity by adding new runways on existing airport property (Fig.…”

Effect of Jet-Exhaust Streams on Structure of Vortex Wakes

“…The results are probably not needed, however, when engines are throttled down, as for approach and landing configurations near airports. Guidelines derived previously [7,18,19] for the motion and spread of vortex wakes for aircraft on approach to an airport are then correct as derived for avoiding vortex wakes of preceding aircraft, and need not be modified. The study did not determine the effect of jetexhaust streams on the decomposition and decay of lift-generated vortex wakes.…”

“…For these reasons, classical roll-up theory was believed to be sufficiently accurate for the estimate of the maximum and the distribution of wake-induced rolling moments in lift-generated wakes of aircraft at cruise altitudes and in the airport environment [3][4][5][6][7][8][9][10].…”

“…For this reason, theoretical and experimental studies of lift-generated vortex wakes have usually not included the effect of jet-exhaust streams on wake structure and on the spread or movement of the hazardous region posed by the vortices in the wake [1][2][3][4][5][6][7]. To be sure that such a neglect was tolerable, a study was made of the effect of engine thrust on maximum measured wake-induced rolling moments on aircraft when they encounter the wakes of preceding aircraft [8].…”

Evaluation of Fast-Time Wake Vortex Prediction Models

“…13,14,15,16,17;18 • Wake zone fast-time models -predict bounded area where wake vortex may reside; may be based on worst case conditions, 19 or could be a deterministic fast time model with bound predictions that are based upon anticipated environmental and aircraft uncertainties; 20 • Probabilistic fast-time models -predict the probability that a wake vortex will be a particular distance from the flight path and the probability that the wake vortex has weakened below a specified strength. Probabilistic models can be entirely data driven or use either a single or an ensemble of deterministic models as its basis.…”