Pilot assistance system reduces noise

For the flight tests, 23 pilots from the airlines Swiss, Edelweiss and Lufthansa were divided into two groups. Fourteen pilots used the LNAS assistance system and were shown the best times for extending the flaps and landing gear, thus completing an approach optimised for low noise and fuel consumption. The other nine attempted to fly as quietly and fuel-efficiently as possible without LNAS computer support. On each approach, the aircraft was flown by one of the participating airline pilots, with a DLR test pilot acting as co-pilot. Each of the 70 approaches considered began at 7000 feet (2100 metres above sea level) and 220 knots (approximately 400 kilometres per hour). Forty-three approaches were flown using LNAS and 27 without LNAS. The A320 ATRA was stationed at and operated from Dübendorf Air Base, where scientific research campaigns are regularly conducted.

The flight data evaluated by DLR shows that the pilots using LNAS flew the descent much more uniformly and precisely than the colleagues flying without the assistance system. The changes in airspeed were also significantly smoother when using LNAS. The use of noise-intensive airbrakes was completely eliminated on approaches with LNAS.

Measurement chain along the approach path to runway 14 at Zurich Airport. Graphic: Empa.

The focus of the LNAS assistance system is the reduction of acoustic outliers, which contribute disproportionately to noise pollution. Some particularly loud approaches are especially annoying for those residing near the flightpath. Using LNAS, it was possible to avoid these outliers and thus make even the loudest approaches up to three decibels quieter, which corresponds to a reduction of the perceived volume by approximately one third.

The noise emissions of the flight tests were recorded by six measurement stations located between approximately 6.3 and 18 kilometres before the touchdown point. For this purpose, measuring points were also set up on German territory in the district of Waldshut. At the most distant measurement points – Hasle and Steinrütte – located approximately 18 and 16.5 kilometres from the touchdown point, respectively, a mean reduction of around one decibel was observed. Between Kaiserstuhl and Weiach, approximately 10 to 13 kilometres before the touchdown point, the average difference in noise levels was up to 1.8 decibels.

Noise levels (integral of the entire overflight) along the approach route to runway 14 at Zurich Airport – with LNAS (blue) and without LNAS (red). Image: Empa.

By comparing the approaches performed by the two groups of pilots, the researchers also determined the average fuel savings that can be achieved with LNAS. During the last 50 kilometres before the runway, the pilots with LNAS needed an average of 8.9 kilograms less kerosene than those flying without LNAS. Extrapolated to all Swiss A320 flights (flight movements in 2017), LNAS could thus save around 500 tonnes of kerosene per year. Since the assistance system can be used at cruising altitude, that is, from 200 kilometres before the runway, the potential for savings is even greater. Conservatively calculated, the annual savings amount to 3000 tonnes of kerosene, which corresponds to about 9000 tonnes of carbon dioxide, even if only the Swiss A320 fleet were to be equipped with LNAS.

The delivery of the final report to FOCA marks the conclusion of a three-year research project involving the Swiss SkyLab Foundation, Empa and DLR. During the five-day test flight campaign, the Swiss Air Force made its Dübendorf Air Base available for the stationing of DLR’s ATRA research aircraft. Skyguide provided advice and assistance during the development phase and enabled the large number of approaches to be conducted.

Simulation of aircraft noise on the basis of measured data using Empa’s sonAIR simulation program. Dotted line: with LNAS; solid line: without LNAS. At 24 kilometres from the runway, in the middle of the southern Black Forest, a significant noise reduction is apparent (dark blue). Graphic: Empa