The ATRA conducted three days of noise-minimising landing tests at Frankfurt Airport. (DLR)
Researchers in Germany have tested a new ‘pilot assistance system’ designed to reduce noise during aircraft landings while saving fuel. The tests, which were conducted as part of a joint research project by the Deutsches Zentrum für Luft- und Raumfahrt (DLR) research centre and the German airport and regional forum Umwelt- und Nachbarschaftshauses (UNH), were conducted using a modified Airbus A320 Advanced Technology Research Aircraft (ATRA) at Frankfurt Airport. UNH has contributed Euro 560,000 towards the project.
Landing an aircraft can generate a high volume of noise on the ground below depending on the speed and height of the aircraft, the thrust from the engines and the deployment of flaps, undercarriage and speed brakes. Landing is also the busiest part of the flight for pilots who have many other things to think about in addition to how much noise the aircraft is making.
To address this problem, DLR have created the Low Noise Augmentation System (LNAS) pilot assistance system which is displayed on the flight deck to show the pilot exactly when each noise-mitigation manoeuvre should be carried out. Displayed via the pilot’s electronic flight bag (EFB), the LNAS shows the pilot sees the ideal vertical approach profile separated into various phases on the display, showing when speed should be adjusted and flaps or undercarriage deployed. The LNAS can be used to guide pilots from cruising altitude down to stabilisation height 1,000 feet above the ground with minimum thrust, resulting in the lowest possible generation of noise and consumption of fuel. "If the pilot follows the instructions at the precisely calculated times, in line with the approach controller's instructions, this part of the landing phase can be completed with the engines at flight idle," explains Sven Oppermann from the DLR Institute of Flight Systems.
From PhD to flight demo
The LNAS shows the pilot what needs to be done at each stage of descent to reduce noise. (DLR)
The LNAS concept originates from a doctoral research project at the DLR Institute of Flight Systems in Braunschweig. Prior to this year’s flights using the A320, the system was tested in 2014 using the Air Vehicle Simulator (AVES) at the DLR Institute of Flight Systems. Four external pilots and three DLR test pilots each carried out 11 simulated descents into Frankfurt Airport under varying conditions, such as different wind speeds and glide slope angles.
Initial evaluations from these tests showed that using the assistance system could save up to 11kg of fuel per descent. The use of speed brakes, which generate a great deal of noise, could be avoided by using the assistance system. In addition, the approaches were more precise and the potential for reducing noise levels during descent was demonstrated.
After being tested in a simulator the LNAS was trialled in initial research flights with no surrounding air traffic. This was followed by three days of test flights conducted at Frankfurt from 26-28 September.
DLR’s ATRA Airbus A320-232 research aircraft. (DLR)
The tests were conducted using the ATRA Airbus A320-232 flying test bed which has been in service with DLR since 2008. ATRA has several cockpit interfaces, additional data links and a head-up display. The test aircraft has been modified to include energy supply and cooling systems, data system recording, air data and inertial systems, video cameras, working stations for flight test engineers and researchers, intercom system, racks for instruments, additional computers or other equipment, additional navigation and datalink antennas. There is also a ground station with data processing and telemetry links to the aircraft, as well as a full flight simulator.
The ATRA aircraft has been modified for research projects. (DLR)
In addition to testing low-noise approach and departure procedures, ATRA is also used for a number of different research areas:
- Testing of aeroelastic measurement techniques
- Research into inner space acoustics
- Airframe noise measurement
- Measurement of turbulence at the wing and at the tailplane
- Testing of new measurement techniques, such as PIV (Particle Image Velocimetry), an optical method for measuring velocity fields
- Measurement of wake vortices and research into flight control commands for passing through them
- Atmospheric and engine measurements
- Research into pilots' workload and division of work
- Testing navigation and communication technologies for aircraft
Keeping the noise down
The pilot assistance system is displayed on the pilot’s electronic flight bag screen. (DLR)
The tests comprised five test flights per day, including take-off, approach and go-around using the northwest runway at Frankfurt Airport. The flights were co-ordinated with the airport, together with the German DFS (Deutsche Flugsicherung) air traffic control service. During each flight, the DLR flight captain was accompanied by four pilots who each conducted two approaches in normal operational conditions with and without the pilot assistance system. Data was recorded from each flight showing altitude and speed and their effect on noise, fuel consumption and flight time within the constraints of real flight operations.
Landings are not the same each time, as they are affected by factors such as weather conditions, visibility, aircraft weight and instructions from air traffic control. Researchers at DLR wanted to learn how the new advice system could cope with such variables. LNAS includes preliminary path planning, runtime correction and energy-based display components. Using the data generated from the aircraft, a simplified simulation model is generated for the preliminary path planning of an ideal vertical approach profile including optimum points for deploying the flaps and landing gear, and speed setpoints. If the pilot carries out manoeuvres in line with the guidelines, the approach from cruising altitude to the stabilisation height can be carried out with minimal thrust (engines at flight idle). During the approach, the wind values are recorded at each new altitude which are used to improve the wind profile for the entire approach. Should the pilots carry out an action too early or too late or there are new instructions from the approach controllers, the recommended sequence of actions can be constantly adapted and changes made to the individual action timings. The optimisation goals for the adjustments adhere to the stabilisation conditions at the 1,000-foot gate, the lowest possible engine speed and the avoidance of spoiler deployment.
Independent verification of the effectiveness of the system in reducing noise was provided by a network of noise measurement stations set up around Frankfurt airport. The results of the project are to be presented at the fourth International Conference on Active Noise Abatement (ICANA 2016) to be held in November.
Greener by Design
The Society will be hosting its annual Greener by Design Conference on 17-18 October 2016 where noise and air quality issues will be discussed. Book your place to attend and hear from leading aircraft manufacturers, researchers and airport directors.