By Adeniyi Onifade
Aircraft noise can be disturbing to those who live around airports. For decades, the industry has been working to reduce noise, with significant progress: noise levels have halved in the past 10 years. It is estimated that the noise footprint of each new generation of aircraft is at least 15% lower than previous models.
In 2013, the International Civil Aviation Organization (ICAO), the United Nations’ intergovernmental body on aviation, introduced Chapter 14, a new standard in noise reduction. It stipulates that new aircraft models need to be at least seven decibels quieter than those built to the previous Chapter 4 standard. This ensures the quietest technology will be used on future aircraft.
The certification was one of several measures to reduce engine noise. In fact, ICAO estimates that between 1998 and 2004, the number of people exposed to aircraft noise around the world was reduced by 35%. It advocates a balanced approach to noise reduction. This combines noise reduction at source with land-use planning and management, operational improvements and flight restrictions. The aim is to maximise the environmental benefit, while minimising cost.
Technology
Research into noise reduction has been extensive, examining factors like the amount of air travelling through the engines, the size of the fan blades in the engine, the position of the engine on the aircraft body and even the size and number of flaps that help control the wing shape. The latest large aircraft, the Boeing 787 and Airbus A380, have remarkably small noise ‘footprints’. The new Bombardier CSeries makes use of new Pratt & Whitney ‘geared’ turbofan engines, which further cut noise and emissions.
The industry has been working hard to make aircraft a further 50% quieter. There is a powerful incentive to continue tackling this issue, as concerns over noise pollution can – and do – affect the viability of airport expansion plans.
Air traffic management
Controlling where planes fly during take-off and landing has an important impact on noise pollution. The placement and use of runways is fundamental, for example, planes travelling at night can travel over seas or lakes to reduce the impact of noise.
Air traffic management maps out flight tracks that avoid the most densely populated areas. Recent developments in navigation performance mean that aircraft can now follow precisely designated tracks. This avoids track spreading and the resulting ‘spaghetti’ radar flight track maps but can mean that a smaller number of residents are subjected to a higher number of flyovers. Air traffic management therefore needs to be undertaken in close consultation with community groups. Issues such as the relative benefits of track concentration versus track dispersion need to be considered.
With support from the air navigation service providers and airport operators, airlines and pilots can implement noise reduction procedures, such as reduced thrust take-off, displaced landing thresholds and continuous descent operations.
Land-use planning
In parallel with aircraft noise reduction, land-use planning is crucial for minimising the number of people exposed to aircraft noise. Airports need to work with local authorities to implement zoning rules in affected areas. Effective land-use planning can discourage or prevent inappropriate new residential, health or educational developments, and encourage developments that are not sensitive to aircraft noise, such as light industry or storage areas. In some areas, sound insulation and ventilation is required for new or existing homes to reduce indoor noise levels.
Unfortunately, in most cases airport operators have no control over land-use planning off the airport site and can only encourage local government to consider airport noise when approving plans for residential and other noise sensitive land use. The industry encourages governments to take a long-term proactive planning approach to land use around airports to ensure that no future development will be negatively impacted by excessive aircraft noise.
A balancing act
In tackling environmental issues, some compromises need to be made. For example, the aviation industry and governments must choose between shortening routes to reduce fuel use and reducing noise, as sometimes the shortest route into an airport flies over communities. This is a delicate balancing act.
Improving air quality
Airports are major business sites with many employees in addition to passengers visiting on a daily basis. Despite aircraft movements being a highly visible part of airport life, local air quality often is more impacted by ground-based emissions from cars, trucks and busses than the emissions of aircraft.
Around airports, the chemical emissions that cause the greatest concern include; nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO) and particulate matter (PM). The impact of other trace emissions, such as sulphur dioxide (SO2), hydroxyl radicals, nitrous and nitric acids, still requires better understanding, but it is currently believed to be negligible.
Cleaner aircraft technology
Since the 1960’s, technical developments mean today’s new aircraft emit 50% less carbon monoxide and 90% less smoke and unburned hydrocarbons than those made 50 years ago. Nitrogen oxide (NOx) levels have also been cut, and modern aircraft now emit 40% less nitrogen oxide than in 1981. As a result of these technological improvements, aircraft can often have less impact on local air quality around airports than road traffic: in some cases, 95% of the local particulate matter comes from cars, trucks and other ground vehicles, rather than aircraft. The International Civil Aviation Organization (ICAO) sets standards for nitrogen oxide emissions and regularly tightens these for each new generation of aircraft. However, there is still more to be done, and the industry has a number of projects underway to reduce its effects around airports further.
Limiting the impact at airports
Aircraft emissions are reduced further when airports provide fixed electrical ground power and pre-conditioned air supplies at the terminal gates. These enable aircraft to switch off their auxiliary power units at terminal gates, reducing fuel burn and pollutants. Taxiing and holding times may be reduced by creating more direct taxiways and holding aircraft at the gate until departure slots are confirmed, generally reducing congestion.
Other sources of emissions that affect local air quality around airports include power plants, ground service equipment and vehicles. Mitigation measures taken by airports and their partners include modernising power plants, ground equipment and vehicle fleets. Diesel and petrol vehicles are being replaced at many airports with those using alternative fuels such as liquid petroleum gas, compressed natural gas, hydrogen, electricity and even compressed air!
Many airports are working with the local authorities to introduce measures to reduce road traffic, improve ground traffic flow and encourage cleaner, greener methods of transport to and from the airport. Airports work with local road and transit authorities to help develop roads and public transport including rail, trams and buses.
Outlook
In the meantime, the aircraft and engine manufacturers are introducing further targets to reduce aircraft emissions, including an additional 80% cut in nitrogen oxide. Airports are also working with the aircraft and engine manufacturers to further reduce emissions and noise impact on local communities. In addition, the efficiency targets to reduce fuel consumption and cut emissions of greenhouse gases will lead to a further reduction in pollutants such as nitrogen oxide and carbon monoxide.