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Approach and landing are among the most labour-intensive flight phases. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) has developed the Low Noise Augmentation System (LNAS) in order to support pilots as they perform the complex procedures required for a low-noise approach. The system uses a display in the cockpit to shows the pilot exactly what action has to be performed and when in order to minimise noise. From 9 to 13 September 2019, DLR is testing the system on board its A320 Advanced Technology Research Aircraft (ATRA) during approaches to Zurich Airport. It is doing so as part of a joint research project with the Swiss SkyLab Foundation and the Swiss Federal Laboratories for Materials Science and Technology (Empa). For these flight tests, the assistance system has been extended with an additional approach procedure that enables optimised, continuous-descent approaches. This uses a high-precision algorithm that facilitates an approach that is as energy-efficient and low-noise as possible.

The optimised approach procedure is being tested during approximately 70 approaches to runway 14 (northern approach from Germany). “We need this many similar approaches to obtain a broad spectrum of data on the functioning of LNAS,” says Fethi Abdelmoula of the DLR Institute of Flight Systems. The test flights are being conducted by 25 participating airline pilots to determine the practicality of the system. The characteristics of each flight will be analysed. For safety reasons, a DLR test pilot will always be present in the cockpit. A team of researchers will be on board during the flight tests to monitor the functioning of the system.

Empa is recording the extent of the noise reduction

Researchers from the Empa Laboratory for Acoustics/Noise Reduction are recording the overflights at seven noise-measuring stations situated along the approach path. The configuration of the A320 ATRA test aircraft is being recorded on each approach, specifically engine power, flap settings, airbrake position and the landing gear deployment. All of these data will be fed into the sonAIR noise simulation program developed at Empa. Using this program, the noise pollution caused by each flight can be modelled on the computer and displayed for selected locations on the ground. The simulation data can then be used to generate detailed noise maps that document the effect of the LNAS assistance system in the region around the airport and show the difference compared to conventional approaches. “SonAIR was developed specifically for noise optimisation during approach and take-off procedures,” says Jean-Marc Wunderli, Head of the Acoustics/Noise Reduction Laboratory at Empa. “This joint project with DLR and SkyLab will give us the opportunity to compare noise pollution shown on our simulations with the real data from the seven measuring stations, and thus check the accuracy of our calculations."

Reducing the number of ‘acoustic outliers’

“Constantly changing conditions such as wind and aircraft weight make the flying of precise vertical profiles in a low-noise approach procedure extremely complex,” says DLR test pilot Jens Heider, who will be sitting on the flight deck of the A320 ATRA during the flight tests. An optimal energy balance during the approach is essential to be able to land as quietly as possible. The LNAS assistance system features a display – the Electronic Flight Bag (EFB) – that shows the pilot the optimum times for deploying the flaps and for lowering the landing gear as late as possible, all intuitively and at a glance. “If the pilot follows this guidance, the approach can be carried out from cruising altitude down to the stabilisation height of 1000 feet above ground with minimum noise and the lowest possible fuel consumption,” say Abdelmoula, summarising the benefits.

“The optimal scenario would be a descent with the engines at flight-idle, almost like a glider,” explains Martin Gerber, the Project Manager at SkyLab and the initiator of the further development of LNAS. “We want to use the assistance system to reduce the number of energetically suboptimal approaches and provide pilots the information they need for this purpose in an intuitive and comprehensible way.” Basic physical principles cannot be changed, but the number of acoustically unfavourable approaches can certainly be reduced.
The results of the evaluated flight tests in Zurich are expected in spring 2020. In the medium term, the intention is for LNAS to be implemented as a commercialised solution in the flight management systems used by scheduled airliners.

The research partners

The pilot assistance system LNAS (Low Noise Augmentation System) for Continuous Descent Approach (CDA) has been developed as part of a three-year project initiated by the Swiss SkyLab Foundation, in a consortium with the Swiss Federal Laboratories for Materials Science and Technology (Empa) and the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR). The project is funded by the Swiss Federal Office of Civil Aviation through special funding for air transport (in accordance with Art. 87b BV: Order on the application of the earmarked mineral oil tax for air transport measures to limit the impact of aviation on the environment), the Office of Transport at the Canton of Zurich Department for Economic Affairs, the Swiss Federal Office for the Environment (FOEN), and financial resources made available by the project partners themselves.

The following organisations are also involved: Skyguide, which will control this week’s test flights; Zurich Airport, which is supporting and coordinating the approaches; 25 pilots from Swiss International Air Lines, Edelweiss Air, Condor and Lufthansa, who are testing the new system; the Swiss Air Force, which has allowed the research aircraft to be temporarily stationed at its base in Dübendorf; and Swissport, which will provide ground services.

The SkyLab Foundation was formed in 2016 to promote the scientific, technological and academic utilisation of research flight platforms in Switzerland. SkyLab is associated with the Switzerland Innovation Park Zurich through the Space Hub at the University of Zurich (UZH). Together with the UZH, SkyLab has carried out regular microgravity research flights from Dübendorf Airfield.