When an aircraft is in flight, counter-rotating regions of turbulence, known as wake vortices, are formed behind it. Wake vortices pose a potential threat to following air traffic. Aircraft must therefore keep to a minimum separation distance. These aircraft separations limit the capacity of congested airports in a rapidly growing aeronautical environment as expected after recovery from the pandemic.

The highest risk to encounter wake vortices prevails in ground proximity, where the vortices tend to rebound due to the interaction with the ground surface. To mitigate the risk of wake encounters and to improve runway capacity, DLR has developed the so-called plate lines. Plate lines accelerate the decay of wake vortices in ground proximity, making wake vortex encounters less likely. A plate line consists of several upright plates that are installed beyond the ends of runways underneath the approach glide path (see red dashes in aerial image at the bottom of the page).

Plate Lines Principle

Smart exploitation of vortex dynamics enables this passive, cost-effective, robust, and safe methodology: When wake vortices get close to the plate lines, strong secondary vortices are shed from the plates that actively approach the wake vortices (left top).

The secondary vortices are wrapped around the wake vortices (left bottom). Finally, the secondary vortices propagate actively along either side of the wake vortices and accelerate their decay.

A Decade of Dedicated Research

Since the first idea was drafted in 2008, the functionality of the plate lines has been demonstrated in towing tank experiments, massive parallel numerical simulations, and flight trials with the HALO research aircraft (photo on the left). A multitude of plate line designs have been elaborated to meet structural and regulatory requirements while maximizing plate line efficiency. As a result, Austrian authorities approved the installation of EASA compliant plate lines at Vienna Airport for tests during landing operations.

Safety Gains Validated at Vienna Airport

In 2019, DLR and Austro Control partnered to accomplish an extensive plate line demonstration campaign at Vienna International Airport (see photo below). Two prototype plate lines were installed underneath the glide path to runway 16 at distances of 400 m and 740 m from the threshold, as depicted in in the aerial image at the bottom of the page.

The analysis of over 1200 wake vortex pair evolutions evinces

• plate lines reduce wake vortex lifetimes as effectively as a high-turbulence regime
• a single plate line appears sufficient
• vortex lifetime reductions increase with aircraft size from 22% for A320 to 37% for B772 aircraft
• plate lines reduce circulation by 50% for Medium follower aircraft landing behind Heavies