Overview of wake-vortex hazards during cruise

A large amount of research effort has been devoted to the hazard posed by l ift-generated vortex wakes of subsonic transport ail-craft during approach and departure at airports. In contrast, only a smell amount of effort has g one into the corresponding potential hazard at cruise attitudes. Because mo re frequent encounters with wakes may occur as the density of aircraft incr eases with time, improved knowledge is needed of the persistence and magnit ude of the hazard posed by lift-generated wakes at cruise altitudes. The pu rpose here is to review and then to extend previous work to characterize pr operly the hazard posed by vortex makes at cruise altitudes. Photographs ar e presented of the various fluid dynamic stages that vortex wakes usually g o through as they age. Estimates made of the potential hazard that each sta ge poses indicate that the rolling-moment hazard during an axial encounter of a vortex wake can be as severe at cruise as far approach at airports; ho wever, as in the airport-approach case, the hazard only persists for severa l minutes (about 20 n mile) behind the generating aircraft. However, the ha zard posed by the downwash in the wake persists for up to tens of minutes ( about 200 n mite) behind the generating aircraft. The downwash hazard is re alized as severe vertical loads. ii technique for avoiding vortex wakes at cruise altitude is described.