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Motorway in the Sky

In pretty much every discussion and article about this runway someone will say something along the line of “it’s all very technical”. One of the “very technical” things that is crucial to this whole discussion is the flight paths or departure tracks being flown by the aircraft, especially on take off which is the noisiest part of any flight.

To use an analogy, flight paths are effectively motorways in the sky. When you plan, design and get permission for a runway a portion of the exercise is the actual concrete structure on the airfield. The rest of it is about where the aircraft will go when they leave the ground on departure (take-off) and approach the ground on arrival. In this way it’s not like when you build a building, it’s more like a motorway.

In the case of the north runway at Dublin Airport the DAA has changed the departure tracks leading to what they describe as residents being “unexpectedly overflown”. What has happened to residents is that a “motorway” has “unexpectedly” been built through their front gardens.

The DAA said that flight paths would be in an entirely different place anywhere from 2km to 10km away from where they actually built them. If it was indeed a road that was built, it would be utterly unacceptable to put it somewhere other than where the planning permission stated. The principle is exactly the same for the flight paths.

There is an important difference between motorway in the wrong place and flight paths in the wrong place that makes this much easier to fix. The concrete doesn’t need to move, only lines on a chart

This is what the charts look like for pilots and ATC. To simplify and declutter them, they ignore almost everything on the ground. In the next section we try to show the history of the tracks DAA has worked up over the years and the effect the changes have on the people who live under the Motorway in the Sky they define.

So what does that look like on the ground?

This is the area to the north of the new runway 28R (Runway numbering explained here). Aircraft departing were supposed to follow this blue line (cyan for the graphic nerds). Our randomly chosen example house (not my house!) is 3.5km from the closest point on that track. This was their expectation when the planning was granted. They will hear the aircraft take of, but it is not destructive to their ability to live in their home. Note: this shows only runway 28 departures as this is well over 70% of departures from Dublin Airport due to the prevailing wind.

In 2016 DAA published a noise consultation for their proposed modification of the departure track. This included an immediate 15 degree turn for departing aircraft to allow simultaneous departures from 28R and 28L. All aircraft except transatlantic flights were proposed to use this turn. Now our example house is 1.7 km from the flight path; a lot noisier and the turn reduces climb efficiency of the aircraft so they will now be closer to the ground too. Keep in mind that while DAA carried out this “public consultation”, the planning permission has not been changed to reflect the routes they intend to use.

We’re told that literally at the last review before opening the runway, DAA were told they had missed a safety requirement for operating parallel runways. This requires that the missed approach for 28L (landing traffic on the old runway) and the departure track for 28R must diverge by 30 degrees. Instead of changing the missed approach for 28L (Approximately 1 flight per day on average “goes missed”), they turned every one of the 300+ flights departing 28R shown here on the magenta line.
Our example house is now directly under the flight path and again with lower climb efficiency in a 30 degree turn, the aircraft is much lower to the ground. You may also note the extra track with an additional 60 degree turn to the north meaning within 5km of leaving the runway all eastbound aircraft (the majority) are turned 90 degrees to the runway where no one ever expected them to be.

This is what it looks like for only a handful of departures. Think about 300+ per day! This makes it look like Ashbourne misses it but most of the tracks (heading into mainland Europe and the UK) get within 2km of where 14,000 people live at 3,500 to 4,500ft while operating at climb power (maximum noise). Ratoath (12,000 people) actually has a waypoint (DW991) right on top of it. It’s mostly used by flight heading south; these ones were going to Lanzarote. Yes, we’re turning them north, climbing over 30,000 people to fly south!

This image makes it look like just a few flights, so what’s the big deal, right? Have a look at what 360 flights in 24 hours looks like.

Our Proposal

So what’s the answer. Our proposed departure track is shown here in yellow. The immediate 15 degree turn that the 2016 noise study proposed is not necessary. The yellow track is from the same (ICAO) international standards document: Fly straight ahead <2 nautical miles and then turn 10 degrees. This increases the efficiency of the climb by keeping the wings level longer and then minimizes the turn required.
This permits take off from both runways at the same time, increasing the airport’s departure capacity by at least 50%. This works because all landings occurring on 28L (the old runway) can have take offs in between. This is exactly how it operated before the new runway was built, so DAA and ATC know how to do this already. This will also allow destinations to the south to take off from the south runway and those heading transatlantic, or east to Northern Europe to use the north runway.

So now the airplanes will fly over high density neighborhoods along that pink line, right? Yes, but … Each day 

  • 300+ airplanes will fly along the yellow line while climbing out from a standing start on the runway and climbing all the way making maximum noise.
  • 1 airplane will fly along the pink line and remember these are aircraft that failed to land on 28L and are executing a “missed approach” so they are already flying at least 130 knots at the start of the runway while already 200+ ft in the air so they get to altitude much quicker. They are also only climbing to 4000ft at which point they level off which makes them much quieter. The magenta area is industrial so the first residential areas is reached after 5km.
  • The proposal has already been flight tested in the training simulator for the aircraft that use Dublin Airport and every one can do it on one engine!

Who are we and why do we think we know how to come up with a proposal?

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