The objectives

To support the full scope of noise monitoring activities required by the European Environmental Noise Directive (END) 2002/49/EC as well as the impact assessment of future aircraft noise policies, an adequate noise modelling capability that encompasses all types of aircraft is required.

The current international guidance on aircraft noise modelling (e.g. ICAO Doc 9911, ECAC Doc 29, or Directive 2015/996) is limited to fixed-wing aircraft, thus not covering rotorcraft noise although these are within the scope of the END. Helicopters are generating local noise nuisances and, in the near future, drones and new urban mobility aircraft could create additional ones in densely populated areas. Defining a validated noise modelling methodology for these transport modes is therefore a high priority for the EU.

Between 2015 and 2017, the European Commission DG MOVE tendered the contract MOVE-C2-2014-269 to start addressing this modelling gap, with technical support from EASA. Under this contract, a methodology to compute rotorcraft noise was defined. A generic test plan to acquire helicopter data for noise-modelling purposes was designed and subsequently data was acquired for eight small and medium-size helicopter types that are representative of the bulk of the helicopter fleet operating in Europe. Lastly, a software prototype ‘NORAH’ was developed to compute the noise on the ground for different flight conditions for a single event and for multiple helicopter operations.

The purpose of this framework contract is to build on and extend the work of contract MOVE-C2-2014-269 towards developing and validating a full-fledged noise modelling capability for all rotorcraft,   representative of today’s and of future operations. This will include the underpinning modelling methodology, the corresponding modelling software and the experimental datasets required to address the intended coverage. The experimental tests will include large helicopters to complement previous campaigns, and the further development of the NORAH prototype into a tool which Member States, the European Commission and EASA can use to perform noise impact assessments.

The main tasks and deliverables

Within this framework contract, the following tasks are planned:

• Extend NORAH noise propagation modelling capabilities, e.g. to account for urban environment, for varried terrain and vegetation, and weather effects; 
• Enhance NORAH source modelling capabilities, covering a wider range of flight conditions than available in the noise database;
• Prepare for the rotorcraft noise tests, including: optimisation and update of the generic noise test plan to cover additional flight modes (e.g. hover), identification and prioritisation of the rotorcraft for the noise tests (including EVTOL) ensuring a good coverage of European fleet, investigation of the availability and costs for renting rotorcraft and test sites;
• Expand the helicopter types in the NORAH hemisphere repository by dedicated noise testing;
• Implement the revised noise modelling methodology into a new software;
• Validate the NORAH modelling method against benchmark data.

Research Project Report SC01: Rotorcraft noise modelling method

The first part of the project was completed in September 2021. The main deliverable consists of a revised rotorcraft noise modelling method which covers a broader range of flight conditions and sound propagation effects. The method is available in the report.

A prioritised selection of new helicopter types for inclusion in the NORAH model was developed, together with a generic noise test plan for those. This test plan takes into account the lessons learned from the earlier NORAH noise test campaign such that new data can be acquired in a more cost-effective manner.

The next phase of the project will run until the first quarter of 2024. It will include noise tests for the identified high-priority rotorcraft and the development of a new NORAH software prototype in line with the revised rotorcraft noise modelling method.

Research Project Report SC02: Determination of a human dose-response with respect to single events of Urban Air Mobility-type vehicles

This study presents dose-responses relationships for a new class of aircraft vehicles, namely four drones and one air taxi. Also, a small fixed wing aircraft has been included, and two helicopters that can be considered as reference measurements. A-weighted Sound Exposure Level (SEL) has been used to determine the input sound levels (‘dose’) for the stimuli.

Stimuli have been presented using a headphone as a mono sound on both ears, so no binaural representation was used.

Results from the measurements show expected reported higher annoyance rates for increased SEL values for each vehicle. Differences can be seen between the highly annoyance scores of the helicopters on one hand (lower), and the other vehicles on the other hand (higher), especially in SEL values above 70 dB(A).

For more information, please review the study.

Research Project Report SC03: Upgrading the software tool to NORAH2 and extending the noise hemisphere database

In this specific contract, the contractor applied the new methods and algorithms identified in Specific Contract SC01 for creating a new version 2.0 of the NORAH software. The contractor also updated the NORAH noise hemisphere database with the data collected from dedicated flight tests, using helicopter types that are representative of the bulk of the helicopter fleet currently operating in Europe, such as the Guimbal Cabri G2, the AugustaWestland A109 and the Sikorsky S-92.

NORAH2 software prototype and noise data

The NORAH2 software prototype and noise hemispheres database is a tool that estimates the noise on the ground generated by rotorcraft operations. It was developed as part of this project, which is funded by the European Union's Horizon 2020. The NORAH2 software prototype runs on Windows computers and does not require any installation. More information on how to use the prototype can be found in the User Manual that comes with it, as well as in the NORAH2 video tutorials.

The NORAH2 software prototype and any data contained therein are the intellectual property of the European Union Aviation Safety Agency (EASA) and are licensed free of charge to users. Please note that by downloading the NORAH2 software prototype and data you agree to all of the following terms and conditions:

• To provide the name of your organisation/academic institution, if any, to EASA for statistical purposes.
• To mention that the prototype and any data contained therein originates from EASA in case of use in published studies.
• Not to share the prototype or any data contained therein outside your organisation/academic institution, including by embedding it in other tools or publications, without prior consent from EASA.
• That EASA will not be held liable for any loss or damage resulting from the provision of the NORAH2 prototype and data included therein, or from any use of the NORAH2 prototype (or any part thereof) by you, your organisation/academic institution or your employees. By downloading this document, you release EASA to the fullest extent from any such liability, loss, damage or claim. In particular, no liability can result from differences between the noise results obtained from the NORAH2 software prototype (or any part thereof) and those from other data sources, including any differences with noise measurements.
• To indemnify, defend, and hold harmless EASA officers, employees, and agents from and against any and all claims (including third-party claims), demands, actions, suits, expenses (including attorney’s fees) and damages (including indirect or consequential loss) resulting from your actions.
• That the NORAH2 software prototype and/or the data are offered without any express or implied warranty, including as regards quality and suitability for any purpose. They are in particular not suitable to benchmark rotorcraft from a noise standpoint.
• That you are not entitled to any maintenance or technical support under this license.
• That any dispute regarding this licence shall be subject to the jurisdiction of the Courts of Cologne, Germany, and shall be governed by European Union law, complemented, where necessary, by the national substantive law of Germany.

Please fill in the webform and tick the ‘Agreement to NORAH2 terms and conditions’ box to receive a link for downloading the NORAH2 software prototype and noise data (230 MB).