Approach and landing are among the most complex phases of a flight. In order to enable pilots to fly as quietly as possible, the German Aerospace Center (DLR) has developed a new pilot assistance system that uses a display in the cockpit to show pilots exactly what action is to be taken for a low-noise approach. This is now being tested jointly with Empa researchers at Zurich Airport.
From 9 to 13 September 2019, DLR is conducting a joint research project with the Swiss SkyLab Foundation and Empa to test the new system called LNAS ("Low Noise Augmentation System") on board an A320 DLR research aircraft approaching Zurich Airport. For the flight tests, the LNAS assistance system was also extended by a further approach procedure for optimised continuous descent flights and equipped with a new high-precision algorithm to enable an approach that is as energy-optimised and low-noise as possible.
The optimised approach procedure will be tested on the basis of around 70 approaches to runway 14 (north approach, coming from Germany). "We need this number of similar approaches in order to obtain a broad database on the function of LNAS," explains Fethi Abdelmoula of the DLR Institute of Flight Systems Technology. The flights will be tested for their suitability for flight mechanics as well as from the point of view of 25 participating airline pilots. A DLR test pilot always sits in the cockpit as a safety pilot. A team of scientists accompanies the flight tests on board and monitors the functioning of the system.
With seven noise measuring stations along the approach axis, researchers from Empa’s Acoustics and Noise Reduction Department record the overflights. During each approach, the configuration of the test aircraft is recorded, i.e. the power of the engines, the position of the landing flaps, the airbrakes and the landing gear. All these data flow into the noise simulation program sonAIR developed at Empa. With the help of the program, the noise pollution caused by the flight can be modelled on the computer and displayed for individual locations on the ground. Detailed noise maps are then produced from the simulation data, documenting the effects of the LNAS assistance system in the region around the airport and showing differences to conventional approaches. "sonAIR was developed specifically for noise optimization in approach and departure procedures," says Jean-Marc Wunderli, Head of Empa’s Acoustics and Noise Reduction Department. "The joint project with DLR and SkyLab gives us the opportunity to compare the noise pollution from our simulation with the real data from the seven measuring stations and to check the quality of our calculations".
"The constantly changing conditions such as wind and flight weight make the precise flying of vertical profiles of a low-noise approach procedure highly complex," says DLR test pilot Jens Heider, who sits in the cockpit of the A320 during the flight tests. In order to be able to land as quietly as possible, an optimum energy balance during the approach is essential. The LNAS assistance system shows the pilot intuitively and at a glance on a display the optimum times for setting the landing flaps and extending the landing gear as late as possible. "If the pilot acts according to these specifications, the approach can be carried out from cruising altitude down to the stabilisation altitude of 1000 feet above ground with minimum noise development and the lowest possible fuel consumption", Abdelmoula summarises the advantages.
"A descent in neutral would be optimal, as with a glider", explains Martin Gerber, project manager and initiator of the further development of LNAS. "With the help of the assistance system, we want to reduce the number of energetically suboptimal approaches and provide pilots with the necessary information 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 flight tests evaluated in Zurich are expected in spring 2020. In the medium term, LNAS is to be implemented as an industrialized solution in the flight management system of regular scheduled aircraft. The signs are promising that the innovative solutions developed in this project will be able to fly worldwide.
As part of a three-year research project initiated by the Swiss SkyLab Foundation, Empa, the German Aerospace Center (DLR) and the German Aerospace Center (Empa) further developed the pilot assistance system LNAS ("Low Noise Augmentation System") for the Continuous Descent Approach (CDA).
Other organisations involved are Skyguide, which is in charge of the test flights during this week, Zurich Airport for support and coordination of the approaches, 25 pilots from Swiss Airlines, Edelweiss, Condor and Lufthansa, who are testing the new system, the Swiss Air Force, which is temporarily stationing the research aircraft in Dübendorf, and Swissport, which is providing ground support.
SkyLab is a foundation founded in 2016 to promote the scientific use of air platforms in Switzerland. SkyLab cooperates with the Switzerland Innovation Park Zurich via the Space Hub of the University of Zurich (UZH). SkyLab, together with UZH, has launched the regular weightlessness research flights from Dübendorf Airport.