Overview of wake-vortex hazards during cruise

A large amount of research effort has been devoted to the hazard posed by lift-generated vortex wakes of subsonic transport ail-craft during approach and departure at airports. In contrast, only a smell amount of effort has gone into the corresponding potential hazard at cruise attitudes. Because more frequent encounters with wakes may occur as the density of aircraft increases with time, improved knowledge is needed of the persistence and magnitude of the hazard posed by lift-generated wakes at cruise altitudes. The purpose here is to review and then to extend previous work to characterize properly the hazard posed by vortex makes at cruise altitudes. Photographs are presented of the various fluid dynamic stages that vortex wakes usually go through as they age. Estimates made of the potential hazard that each stage 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; however, as in the airport-approach case, the hazard only persists for several minutes (about 20 n mile) behind the generating aircraft. However, the hazard 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 realized as severe vertical loads. ii technique for avoiding vortex wakes at cruise altitude is described.