Each runway in use at an airport has its own set of flight paths, and each flight path will affect different areas. As the runway in use changes, the flight paths in use will change, and so too do the suburbs affected by aircraft movements.

The runway in use at any given time and the direction of the traffic flow will vary primarily according to the wind conditions at the airport. This is because aircraft must take off and land into the wind for safety reasons. Generally, this means that in:

• Northerly wind conditions at the airport (including north-westerlies and north-easterlies), north flow will be used.
• Southerly wind conditions at the airport, including south-westerly and south-easterly conditions, south flow will be used.

However at times a runway direction may be used with a small amount of tailwind as long as it does not exceed the Civil Aviation Safety Authority’s limits for downwind (tailwind) and crosswind.

When the wind at the airport is calm or light, other factors are taken into account in selecting the runway that will be used. For example, the location of the terminals and the positioning of the taxiways can influence the decision.

At Sydney Airport, the proximity of the terminals to the northern end of the westernmost parallel runway means that in busy periods when south flow is being used, there is not always enough space on the taxiways between the terminals and the runway end for all the waiting aircraft to queue for take-off.

To manage this, some aircraft may need to be held at the departure gate until space becomes available. This can result in delays and create knock-on effects around the country. For this reason, if the wind is not a factor in the decision, north flow will usually be preferred over south flow during peak periods.

The proximity of the terminals to the runway at northern end of Sydney Airport means there is limited space on the taxiways for queuing. Below right: There is much more room for queuing aircraft on the taxiways at the southern end of the Airport.

Our page on Runway Selection discusses how decisions are made about which runway to use.

There is a flight path for aircraft arriving into Sydney from northern ports that brings aircraft through the Sydney heads and southwards down the coast, over water, to arrive on the easternmost parallel runway. This flight path is used when the parallel runways are being used in a northerly direction (“north flow”).

There are times when air traffic controllers need to take aircraft off this flight path to ensure they remain safely separated from other traffic and/or can be efficiently sequenced with aircraft arriving from the east, south and west for landing. When there is poor weather, or in peak periods when there is a high volume of traffic in the airspace, this is more likely to occur.

The image at right shows actual tracks of aircraft arriving into Sydney from the north and travelling southwards to land on the easternmost parallel runway.

When aircraft are diverted from the usual flight path they must be directed over land, and will pass over suburbs such as Rose Bay, Dover Heights and Point Piper. It is not possible to divert these aircraft further east, over the water, because this would create potential conflicts with aircraft that are departing from the easternmost parallel runway and heading north-east. The conflicts could occur because the departures and the arrivals would be at similar altitudes when their paths crossed.

The image below is a zoomed in view of the tracks of aircraft arriving from the north. Aircraft on the usual flight path can be seen flying through the heads and down the coast over water. Aircraft that have been taken off the normal flight path can be seen flying over land.

Aircraft taken off the usual flight path will generally be in the altitude range of 6,000 to 8,000 feet as they pass over the eastern suburbs. This is around twice as high as the jet aircraft that depart over the area.

Air traffic controllers are aware of potential noise implications for the community and do not take aircraft off standard routes unless it is operationally necessary. Unfortunately, when operationally required, this cannot be avoided.

Aircraft that fly over the Blue Mountains from Sydney Airport depart from the westernmost of the parallel runways and turn towards the north-west. They are tracking towards a waypoint located over Katoomba. A waypoint is a set of co-ordinates in the air. This waypoint replaces a non-directional beacon which was a ground-based navigational aid that had been in this location since the 1950s.

Departure flight paths are organised so as to efficiently move aircraft onto their routes. The flight path that passes over the Blue Mountains is assigned to aircraft that are heading for destinations to the west, north and north-west such as Dubbo, Perth, Adelaide, Darwin, Broome, Singapore, Kuala Lumpur, Dubai, Abu Dhabi, Hong Kong and Shanghai, for example.

While this is not a new flight path, advances in navigation technology used by modern aircraft mean that aircraft are now able to fly flight paths more precisely and this has resulted in increased concentration of flight paths over the years, including this one.

Altitudes

The altitudes of traffic departing Sydney Airport will vary according to which runway the aircraft has departed from because this affects the number of track miles the aircraft has flown before it reaches the Blue Mountains. The more track miles flown, the more time the aircraft has had to increase altitude and the higher it will be over your area.

Altitudes will also vary according to other factors such as the weight of the aircraft and how heavily laden it is. For example, long-haul aircraft departing for Dubai will be much heavier than smaller aircraft heading to Perth or Adelaide due to fuel load and aircraft size and these differences in weight alone will affect an aircraft’s climb rate.

Even the atmospheric conditions at the time can play a part. When the weather is warm, the air is less dense and therefore there is less lift and the aircraft climbs more slowly. Due to these variable factors the altitudes quoted below are not limits and some aircraft may be higher and some lower that the ranges given.

Jet aircraft departing towards the north will generally be within the altitude range of 10,000 to 20,000 feet. Turbo-prop aircraft that have departed Sydney Airport may range from 7,000 to 15,000 feet.

For aircraft departing towards the south, jets will generally be from 15,000 to 25,000 feet. Turbo-prop aircraft will usually be from 10,000 to 15,000 feet.

Many Blue Mountains residents have told us they feel jet aircraft are lower now than in the past. We conducted an investigation into this question, looking at altitudes of aircraft that passed within a five kilometre radius of Blaxland in January of each year from 2012 to 2018. The investigation found variation in altitudes between different aircraft types but relatively little variation within the same aircraft type. The variation in altitudes between aircraft types can be attributed largely to the differing maximum take-off weight of each type. Heavier jets demonstrated a poorer climb performance than lighter jets.

The investigation also found a marked increase in airlines using A380-800 aircraft – from 23 flights in January 2012 to 126 flights in January 2018. As the A380 is the heaviest jet and as the study indicated that they have the lowest average altitude, the increased use of this aircraft type is likely to be a major contributing factor to the community’s perception that altitudes over Blaxland have decreased.

Prospects for change

Airservices has investigated whether it would be feasible to move the Katoomba waypoint. The investigation found that this would adversely impact on safety and would not be operationally feasible due to the constraints of military airspace restrictions and air traffic control sector boundary and route segregation requirements. It would also negatively impact on communities closer to Sydney Airport where the noise levels would be higher than those currently experienced in the Blue Mountains.