Reduction of uncertainties in prediction of wake-vortex locations

Lift-generated vortex wakes of subsonic transport aircraft are known to pose a rolling-moment hazard to in-trail following aircraft. Hazardous wake encounters are now avoided by maintaining in-trail separation distances that are larger than needed for other operational considerations. To increase airport capacity, considerable effort has been devoted to the development of techniques and procedures by which vortex wakes can be accurately located as a function of time, so that following aircraft can avoid them with less in-trail spacings. To improve the accuracy with which vortex wakes can be located, a study of the uncertainties associated with the determination of the time-dependent location of vortex wakes and on ways to reduce the uncertainties are reported. It is found that it is beneficial to reduce the uncertainties as much as possible by application of technology currently available for aircraft guidance and for measurement of wind velocity along the flight corridor by aircraft. It appears, however, that the growth in, and spreading of, the size of the hazardous region surrounding wake vortices is so rapid that it currently prevents sizeable increases in the capacity of runways at airports as they now operate. Therefore, if airport capacity is to be significantly increased, it is concluded that it will be necessary to also introduce some other system of sequential flight corridors such as the ones illustrated here, for example, to provide more lateral and vertical distance between the flight paths of aircraft so that wake encounters are avoided.