Australia has one of the most modern and quietest fleets of aircraft operating in the world. Despite this, airlines still continually seek ways to minimise the noise impact of their aircraft through noise abatement procedures.
Aircraft operating in Australia have to meet international noise standards. Many airline operators have purchased quieter aircraft in response to community concerns, or have re-organised their fleets so that quieter aircraft operate at sensitive times, such as at night or weekends. Some airlines have invested in high technology navigation aids that ensure, as far as possible, aircraft avoid flying over densely populated areas.
Where able, airline operators also undertake, a Continuous Decent Approach (CDA) this enables aircraft, through the use of technology, to glide into the airport in one smooth descent.
This minimises power settings, reduces engine noise and allows landing gear to be deployed later, thereby reducing noise. However, in heavy traffic conditions, it is not always possible to deploy CDA.
Aircraft travel along designated corridors or ‘flight paths’. These can be a number of kilometres wide – not the straight lines from one point to another often indicated on maps. At most major airports, flight paths are determined by air traffic control. This ensures that aircraft safely avoid noise sensitive areas (where possible) as well as obstacles and other aircraft.
Every runway will have a number of flight paths. These will be used depending on the type of aircraft, the volume of traffic, type of navigation aid being used, and current weather conditions. Changes to flight paths are made for a variety of reasons, including safety and the environment. However, changes are not easy to make as they have to take into account the impact it will have on the airport terminal airspace and why aircraft fly where they do.
Take-off and landing
Wind is a predominant factor in choosing the runway that an aircraft may use, given that, for safety reasons, aircraft arrive and depart into the wind. Prevailing winds in many Australian cities are seasonal, which means that one runway may be heavily used during certain months and rarely used at other times of the year. This is also why many Australian airports have more than one runway facing in different directions.
By landing into the wind, aircraft can go slower over the ground and need less runway to slow down. During take-off, headwinds actually help aircraft take off faster. This is because air moving rapidly over the wing gives the aircraft more lift. Taking off or landing with a tailwind is not the preferred procedure. Maximum tailwind limits are set by the manufacturer and the Civil Aviation Safety Authority (CASA).
Arriving aircraft will generally approach a runway in a straight line from around three to four kilometres from the runway end. Residential areas under these approaches, will also be under the flight path of aircraft taking off, and will be those most affected by aircraft noise. Therefore, the choice of which runway to use at any given time will determine which area is exposed to aircraft noise.
Approaching the runway
Pilots occasionally deviate from normal flight paths for safety reasons or upon a request from air traffic control. Generally, this is to avoid bad weather or other aircraft. Aircraft normally come in for landing at a three degree angle. This three degree ‘glide path’ follows a line that descends about 100m every two kilometres.
Fly neighbourly agreements
Many general aviation airports have developed ‘Fly Neighbourly’ agreements. These are voluntary codes of practice negotiated between aircraft operators and communities or authorities that have an interest in reducing disturbances caused by aircraft within a particular area. They may include limitation on flying heights, frequency and areas of operation.
Another aircraft operation that may create noise is ‘ground running’. This is when an aircraft engine is tested while the aircraft is stationary on the tarmac. This allows engineers to verify that aircraft engines are working properly. During ground running, engine settings are increased from idle to a higher power in order to simulate what would happen in a flight. For safety purposes, engine ground running requires facing the engine into the wind. Therefore, the direction of the aircraft and its engine noise will change with wind direction. Due to airline operating schedules, ground running tends to take place at night, although at most airports, engine ground running locations are situated away from the closest residences to reduce noise impacts.