LASER-BASED ANALYSIS of aircraft wake-vortices at London Heathrow Airport suggests that there is little hope of increasing runway capacity by reducing separations.

Researchers believe that real-time provision of vortex information to controllers could sometimes assist with tactical air-traffic control (ATC), but few, if any, strategic gains are realisable. Some standard longitudinal separations may even be slightly increased because of the work.

The research, commissioned from the UK Defence Research Agency (DRA) by the Civil Aviation Authority, supports earlier evidence that the Boeing 757 produces markedly stronger vortices than similar-weight older types - a tangential core velocity of 35m/s (68kt) was recorded at least once.

The DRA team used a 10micron wavelength, infrared, carbon-dioxide laser radar (lidar) of 4W power to measure vortex speeds and patterns at five different sites around Heathrow on 20 days - giving some 2,000 read-outs.

Many of the data produced confirms historical thinking, but they also highlight the occasional phenomenon of vortices, which rapidly and inexplicably collapse after about 60s. They also show up inadequacies in current mathematical models of vortices, which must be addressed if ATC procedures are to be changed.

They confirm as well the importance of crosswinds and turbulence in clearing vortices.

Further DRA work is likely, during which the CAA hopes that it will acquire aircraft-weight and flap/ slat-configuration data from airlines, together with meteorological data from the UK Met Office, to correlate with the vortex observations.

The researchers and the CAA believe that, it is almost certainly practicable to provide controllers with real time vortex information, but Heathrow ATC manager Richard Taylor says: "Any benefits would be tactical in that they could only be applied in the particular weather conditions at a given time. With our weather, we could not see a tactical advantage in terms of reductions in delays being turned into a strategic capacity advantage."

Source: Flight International