Analysis of potential wake vortex encounters at a major European airport

Abstract

Potential wake vortex encounters are investigated that were reported in the timeframe of the years 2013 to 2015 at a major European airport. Almost all of these encounters occurred in close ground proximity such that most pilots conducted a go-around. Wake vortex predictions employing the Probabilistic Two-Phase Wake Vortex Decay and Transport Model (P2P) are used to investigate the incidents in detail and to distinguish whether they actually were wake vortex encounters or whether other effects like wind shear or turbulence might have caused these events. Flight data recorder data was available for the two cases that took place in 2015 such that a very detailed analysis of the incidents could be conducted. In both cases wake vortex encounters appear highly plausible and the flight tracks through the vortices could be reconstructed in good agreement with wake vortex predictions and recorded aircraft reactions. In two further cases in the year 2014 the types of the involved aircraft as well as the encounter altitudes were known whereas for seven other cases the flight altitudes were not known exactly and had to be assumed. In total, 8 of the 12 investigated encounters appear plausible or are at least possible whereas 4 cases have to be excluded. In 5 of the 8 plausible wake vortex encounters the meteorological situation was characterized by weak crosswinds combined with tailwinds. This combination is deemed favorable for encounters because on one hand weak crosswind may compensate the self-induced lateral propagation of the upwind vortex, such that it may hover over the runway directly in the flight path of the following aircraft. On the other hand, tailwinds limit the propagation of so-called end effects – disturbances caused by the breakdown of lift during touchdown traveling against flight direction and weakening the vortices in ground proximity.