Noise Integrated Routing System (NIRS) & NIRS Screening Tool (NST)

Noise Integrated Routing System (NIRS) Version 6.1

The Noise Integrated Routing System (NIRS) is a noise-assessment program designed to provide an analysis of air traffic changes over broad areas. It is intended to work in conjunction with other Air Traffic modeling systems that provide the source of routes, events, and Air Traffic procedures such as altitude restrictions. In March 2012, NIRS was replaced by AEDT version 2a for analysis of air traffic airspace and procedure actions.

The outputs of NIRS include population-impact and change-of-exposure reports and graphics. Population centroids are evaluated as improved or worsened based on their change of exposure. A hierarchy of rules based on FAA guidance and local requirements are then employed to determine if an airspace alternative is likely to be controversial based on noise considerations. Where possible, the system identifies the principal source of the change of exposure. Having identified the route set responsible for an increase, the air traffic planner can begin the evaluation of possible mitigation alternatives.


NIRS was first developed in 1998 and efficiently addressed the large scale requirements of modeling aircraft noise effects over multi-state regions. In March 2012, NIRS was replaced by AEDT version 2a for analysis of air traffic airspace and procedure actions. Capabilities provided by NIRS are:

  • Altitude-control logic that enables NIRS aircraft to follow user-specified tracks in three dimensions, or to follow “standard” profiles wherever these are consistent with the airspace design;
  • Annualization logic that enables NIRS to mix traffic from different operational configurations in the ratios appropriate to represent average annual airspace and runway usage;
  • The NIRS impact table and impact graph to quantitatively assess differences in noise impacts between alternative airspace designs using specific FAA noise-impact criteria;
  • Change-analysis logic that enables NIRS to specify which traffic elements (out of the many hundreds in regional studies ) are causing significant noise impacts;
  • Various map-based tools for display and query of the underlying track and noise data

NIRS functions and provides familiar menu options. It is intended to have the same look and feel as other window-oriented applications. The main window provides the interface to all of the NIRS programs that:

  • Build and organize a study;
  • Provide error checking of all inputs and outputs;
  • Performs the noise computations;
  • Enable the user to analyze impacts and trace their causes; and
  • Format the output for reports and graphics that may be used in applications such as Microsoft Word, Microsoft Excel and Microsoft PowerPoint.

Model Inputs

NIRS applications are organized as projects. A NIRS project contains all of the input files, output files, reports, and graphics necessary to complete the noise analysis. NIRS utilizes the following inputs:

  • Runway Data
  • Population Census Data
  • Grid Data
  • Scenarios or Design Alternatives
  • Airspace Routes
  • Traffic Files

System Requirements

The current version of NIRS is designed to work on a PC compatible computer with the Linux or Microsoft Windows operating system. The Linux operating system must be either the RedHat 9.0 or greater distribution or an equivalent alternative Linux distribution. The Windows operating system must be Windows XP SP2 or greater. At least 512 MB of RAM are suggested. Approximately 4 MB of free space are necessary to install the NIRS software. Smaller projects may require less than 100 MB of disk space, but larger ones may require more. The noise computation engine has been ported and run on many systems including personal computers, all ranges of workstations, and super-computers.


NIRS was replaced by AEDT 2a in March of 2012.

NIRS Screening Tool (NST) Version 6.1

The NIRS Screening Tool (NST) is an application designed to provide guidance in evaluating potential noise impacts as a result of changes in airport arrivals and departures above 3,000 feet above ground level (AGL). This is accomplished by screening the proposed changes to determine whether there is the potential to increase noise levels over communities beneath the aircraft route. NST has been replaced by the Aviation Environmental Screening Tool (AEST).


Although change actions above 3,000 feet AGL are categorically excluded from FAA Order 1050.1E, Environmental Impacts: Policies and Procedures, new noise introduced over noise sensitive areas has the potential to be highly controversial on environmental grounds. In these instances, the exclusion does not apply and the action should be the subject of a determination of extraordinary circumstances in accordance with Order 1050.1E and an environmental assessment (EA) must be prepared.

In order to assist with this process FAA issued Notice N7210.360, Noise Screening Procedure for Certain Air Traffic Actions Above 3,000 Feet AGL, on September 14, 1990. This notice contained a series of decision tables that airspace planners could consult to determine the potential impact of a proposed change.

In August 1995 the decision tables from Notice N7210.360 were automated in the release of the Air Traffic Noise Screening Model (ATNS) Version 1.0. The ATNS was designed to analyze a single route change at a time. It was not designed to analyze the effects of large-scale airspace changes.

In July 1998, FAA released the Noise Integrated Routing System (NIRS) Version 1.0. NIRS was designed to analyze the effects of large-scale airspace changes over a broad area. It has the ability to assess multiple airports, and thousands of tracks and operations.

The NIRS Screening Tool (NST) is a revision and update of the ATNS. It encompasses the ease-of-use of the ATNS with the noise computing capabilities of NIRS.


NST applies only to simple air traffic changes affecting aircraft actions above 3,000 feet AGL over noise sensitive areas. It is applicable for changes involving aircraft route, aircraft altitude, aircraft mix, number of operations, time of day, or even operational procedures. If a change action involves aircraft departing at altitudes above 10,000 feet AGL, or arriving above 7,000 feet AGL, a noise screen is not needed. (Note: However, if the change is above a national park or wilderness area, it is recommended that screening be conducted up to 18,000 feet AGL.) See ATA-300 memo dated September 15, 2003, for more information.

The NST guides the user step-by-step through the noise screening procedure, performs the calculations, and prepares the report on the findings. Some preparation by the user is required to compile information about the proposed change and the communities that may be affected by it.

Screening Criteria

To determine the possibility for impact, the NST allows the user to compare a baseline and an alternative scenario. For each scenario, all population in the study area is divided into three categories: (1) those receiving an increase in noise exposure relative to the baseline, (2) those receiving a decrease, and (3) those having no change. The rules defining the increase, decrease, and no-change categories and the sources for each rule are given in the following table.

NIRS Screening Tool Impact Criteria
DNL Noise Baseline Exposure Compared to Alternative Exposure
  65 dB or higher 60 to 65 dB 45 to 60 dB
Minimum Change in DNL with Alternative 1.5 dB 3.0 dB 5.0 dB
Level of Impact Significant Slight to Moderate Slight to Moderate

These criteria have been established in accordance with FAA Order 1050.1E, the Federal Interagency Committee on Noise (FICON), and the Final EIS for the Expanded East Coast Plan.


NST has been replaced by the Aviation Environmental Screening Tool (AEST). AEST, like NST before it, is currently available only for use by FAA employees. To obtain AEST, persons in FAA service areas or facilities may contact the Environmental Program Group for information.