Plate Lines – Mitigating Wake-Turbulence Risk
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
The World ATM Congress in Madrid is the largest event in the field of air navigation and air traffic control. From June 21st to 23rd in Madrid, it combines a major exhibition with a conference. Almost ten thousand specialist visitors from all over the world use this annual opportunity to familiarise themselves with the latest trends and developments in this field. AT-One will be there with several research exhibits at booth no. 351.
Ready for Permanent Installation
A plate line comprises eight upright plates that are positioned underneath the approach glide path. Each plate consists of four frangible aluminium lattice masts covered by nine aluminium sandwich panels with a honeycomb core. The plate design for permanent installation at an airport was developed in close collaboration with experts from Austro Control to ensure compliance with all airport-specific requirements.
Increasing Runway Throughput
By accelerating wake vortex decay, plate lines reduce the encounter risk during final approach. This risk mitigation can be translated into five plate line use cases.
Use case I yields an improved safety performance for arrivals just by installing plate lines underneath the glide path.
Use case II unleashes simultaneous gains of capacity and safety: The introduction of the pairwise separation scheme RECAT-EU may facilitate up to five additional landings per hour, while the plate lines fully compensate the estimated rise of uncritical encounters by 60%.
Use cases III and IV enable additional capacity gains by translating the accelerated wake vortex decay into reduced separations or by extending the application range of the so-called REDSEP scheme to situations with weak winds.
Use case V employs pairwise dynamic separations to reduce aircraft separation tactically depending on the prevailing weather conditions and the resulting wake vortex behaviour.
See our white paper at https://elib.dlr.de/185982 for more details on plate lines and their associated use cases.
SESAR Joint Undertaking Projects EARTH & SORT
The current endeavour has received co-funding from the European Union’s Horizon 2020 research and innovation programme under grant agreements No 731781 and No 874520 within the SESAR JU projects Increased Runway and Airport Throughput (PJ.02 EARTH) and Safely Optimized Runway Throughput (VLD3-W2 SORT).
As the technological pillar of the Single European Sky (SES) to modernise Europe’s air traffic management (ATM) system, SESAR is now making significant progress in transforming the performance of Europe’s ATM network. The SESAR Joint Undertaking (SESAR JU) was established in 2007 as a public-private partnership to support this endeavour. It does so by pooling the knowledge and resources of the entire ATM community in order to define, research, develop and validate innovative technological and operational solutions.