Abstract
To mitigate the risk of wake vortex encounters during final approach, so-called plate lines have been developed. Data collected during a six-month measurement campaign at Vienna International Airport are used to assess the potential for reducing minimum aircraft separations facilitated by plate lines during approach and landing following the re-categorisation (RECAT-EU) methodology for revised wake turbulence categorisation. To ensure that no other parameters controlling wake vortex decay bias the analysis, it is verified that wind speed, atmospheric turbulence, thermal stratification and flight altitude reside in similar ranges with and without the plates. The analysis follows the steps of the RECAT-EU method to generate non-dimensional so-called reasonable worst-case circulation decay curves; one as a reference for nominal operations without plates and one representing the accelerated wake vortex decay brought about by the plate lines. The difference between the two circulation decay curves corresponds to the non-dimensional time-based aircraft separation reduction potential that can be translated into distance-based separation gains. Depending on the particular RECAT-EU category combination, the attained aircraft separation reduction potential ranges between 12% and 15%. Constricting the analysis to wake vortices generated by one aircraft type representing the Upper Heavy RECAT-EU category, the separation reduction potential amounts up to 24%.
Highlights
As an unavoidable consequence of lift, every flying vehicle generates counter-rotating regions of turbulence known as wake vortices
As the re-categorisation initiative (RECAT)-EU safety case has been approved by authorities and as it is applied in operations at several airports, the approach of the current assessment of the aircraft separation reduction potential facilitated by plate lines is to adopt the RECAT-EU methodology as closely as possible
During a six-month campaign at Vienna International Airport, the wake vortex behaviour of approximately 9500 landings with and without plates was measured simultaneously by three lidars complemented by a comprehensive suite of meteorological instrumentation
Summary
As an unavoidable consequence of lift, every flying vehicle generates counter-rotating regions of turbulence known as wake vortices. Savaş (2005) provides an overview on experimental investigations on wake vortex alleviation starting in the 1970s with various concepts investigated by NASA comprising mass injection, oscillating devices, wing tip modifications, vortex interactions and end plates In total he lists more than 30 references that can be categorised either as passive schemes enhancing inherent instability mechanisms of vortex systems or as active systems that rely on hastening selected instabilities by forcing the vortices individually or as a system. Plate lines accelerate the circulation decay of wake vortices that may rebound into the flight path of following aircraft due to their interaction with the ground surface (Holzäpfel et al, 2016; Stephan, Holzäpfel, & Misaka, 2013, 2014; Stephan et al, 2014). A comparison of the initial circulation values estimated independently from lidar measurements and Mode S data is presented
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