Decisions related to reducing the environmental impact at airports, mainly related to noise and emissions, are usually based on operational changes. These are often made on the basis of a wide range of strategic, economic, capacity and impact-related information. Considering interdependencies or trade-offs of the proposed action(s) and/or alternatives is essential when using results to influence decision-making or conduct an environmental assessment in order to avoid, where possible, any unintended consequences.

To better illustrate the above: the airports need to assess the benefits (e.g. noise reduction) vs disadvantages (e.g. more fuel burn/carbon) when operational changes are adopted. Yet, the approach could be for trading fewer emissions with (more) noise. Therefore, answers need to be provided on when to conduct a trial on interdependencies and how to do it, what actors to involve, what results to expect, what tools to use, etc.

It is important to realise that aircraft operations involve many stakeholders – airlines, authorities/regulators, Air Navigation Service Providers, the airports, residents, associations. Each of these stakeholders looks at operational and environmental aspects differently.

Annex B.1 Stakeholders and CEM and B.6 Decision making process (PDF) provides more detailed information on stakeholders and decision-making involved in the airport operations.

A review of Tools used for noise or/and emissions, screening existing knowledge

Various information is required for the development of environmental studies and/or assessments, including trajectories, flight plans, aircraft engine specifications, aircraft performance data, as well as statistical data regarding, for example, aircraft schedules and the number of the population living in the proximity of airports.

Almost all necessary and relevant data regarding interdependencies' studies can be grouped into three categories: flight information, noise and emissions outputs (that characterise the main focus) and the use of methods to determine impacts (e.g. metrics, models, tools, databases).

However, to assess interdependencies, the use of a tool that integrates all environmental consequences is needed. Here, more research is required to develop an environmentally friendly, easy to use tool that will assess noise and emissions at the same time.  

It is important to underline that whilst some tools do exist (e.g. the FAA’s Aviation Environmental Design Tool and EUROCONTROL’s IMPACT tool) they are quite complex and generally used by the most experienced airports. What is needed is a more user-friendly set of tools that go beyond quantifying noise and emissions outputs to assessing impacts (e.g. on health) in a common framework

Information on aircraft operations, noise and emission outputs and assessment tools/metrics, associated with noise and emissions trade-offs can be found in Annex B.2 Operations.

The academic study and the airport survey results show that interdependencies between noise and emissions often involve operational procedures in the Landing and Take-off (LTO) phases. Most of these deal with departure procedures, where the noise versus emissions trade-off is better illustrated.

Figure 1 provides a schematic overview of departure and arrival procedures. Though the figure is on noise mitigation opportunities, it should be emphasised that emissions also play a role here, being linked to aircraft operations.

For departures, (changes in) the following operational procedures are relevant:

• Reduced or flexible thrust;
• Noise Abatement Departure Procedures.

For arrivals, (changes in) the following procedures are relevant:

• Continuous Descent Operation (CDO);
• Low power/low drag;
• Reduced landing flaps.

The effect on noise and emissions of the above procedures are further elaborated in Annex A Academic study and Annex B Airport review - operations - metrics and tools. Illustration on Catania case-study is provided at Annex C Catania Airport case study. The examples given through ANOTEC and NLR research provide different angles to assess noise and emissions trade-offs.

Figure 1. Overview of different departure and approach procedures (Source: Sustainable Aviation, 2017)

More detailed information on noise and emissions interdependencies in airport departure, arrival and ground operations is provided in Annex B.2 Operations.

The academic study undertaken by ANIMA (Annex A Academic study) was a detailed assessment of archived, peer-reviewed academic literature in order to present a snapshot of current knowledge and understanding of the interdependencies between aircraft noise and exhaust emissions and the subsequent impact on communities. Examples of interdependencies between CO₂(fuel) and NO_x(AQ) are provided.

The study primarily confirms that noise and emissions are frequently considered independently and not in a holistic way. Indeed, it appears that only a few academic studies have sought to quantify the trade-offs, though a number have provided a qualitative/hypothetical assessment. This reflects the approach of regulators, who also set independent standards for noise and emissions. Such approaches and the increasingly stringent noise and emission standards have been successful in reducing the overall environmental impact of aviation. The recent peer review and accessible industry literature contain little evidence of a comprehensive noise/emission trade-off analysis.

Generally, published studies that have examined the effect of changes to how aircraft operate in and around airports have focused on saving CO₂ or NO_x. Only recently, particulate matter (PM) has been factored into the equation primarily through the application of FOA3 (Methodology to estimate particulate matter emissions from certified commercial aircraft engines. Wayson et al., 2009) rather than the actual emission of nvPM (mass and number). There is also little evidence that existing work has considered secondary PM formation, which could be an order of magnitude larger than the primary emission. This may have profound implications when considering operations with low thrust settings (i.e. taxi operations).

The existing literature is also relatively silent on examining any trade-offs or interdependencies between the impact of noise and emissions. Arguably, it impacts aircraft noise and emissions, which is essential and should be factored into future trade-off/interdependency analysis. Though, it is recognised that this is not a simple or straightforward task and may go beyond many airports' capability.