A parallel runway adds capacity. Land on one and take off from the other, and each runway does one job: more flights, and easier to run. At the busiest times, go further: planes off both runways at once.
But a parallel runway isn’t just one more runway. It changes an airport so much that it has a manual all its own, from ICAO, the United Nations’ aviation agency in Montreal, which writes the international standards. Each way of using the two runways comes with a safety rule in it.
Planes taking off from both runways at once must go different ways. Their tracks must split by at least 15 degrees.
Landing on one and taking off from the other has a rule too. Now and then an arriving plane has to abandon the landing and go around. It must not run into a plane taking off from the other runway. So the go-around and the departure must split by at least 30 degrees.
That’s how Heathrow runs its two runways, landing on one and taking off from the other. In 2024 it carried 83.9 million passengers. Dublin carried 34.6 million.
The splits provide the capacity. The capacity requires the splits.
The rules say the tracks must “diverge”. Remember that word. They don’t say which one has to turn.
In 2016 daa, the airport operator, consulted the public on the North Runway’s routes. Its display panels said international standards require the planes to diverge by at least 15 degrees, “approximately one nautical mile after take-off”. The maps showed a gentle 15-degree split, because that was “the minimum requirement”. The booklet never mentioned Meath, which is where the planes go now (story 2 has who was asked).
In 2017 daa’s noise consultants wrote it up. The Irish Aviation Authority, they said, would require a divergence of 15 degrees or more. The turn would come at about a mile from the end of the runway, which they “considered the earliest point that a turn is likely to be possible”. That mile was an assumption. The ICAO manual says “immediately after take-off”.
Fifteen degrees at a mile is over mostly empty fields and solar farms.
Thirty degrees appears nowhere in anything the public was shown.
In August 2022 the runway opened. The planes turned early, by 30 degrees, and some by 75. The neighbours had been told 15 degrees at a mile, and 75 for some (story 2 has the 75).
So 15, 30, whatever, right? Thirty degrees is a straight line to Ratoath, where over 10,000 people live, and the routes pass within 3 km of the centre of Ashbourne, around 16,000 people.
Where did 30 come from? The second rule. Not the planes leaving together at the busiest times: the rare plane that abandons its landing on the other runway.
Must split. Not: the departure must turn.
In November 2023 the Aviation Authority wrote to an Oireachtas committee. “In principle, the missed approach procedure for 28L could turn left to ensure a divergence of at least 30 degrees from aircraft departing on runway 28R which continue straight ahead.” (The missed approach is the go-around. 28R is the North Runway, 28L the other one.)
Straight ahead. As assessed. As permitted.
In March 2026 the Authority’s witness said it again, to the committee’s face. The go-around could turn 30. Or the go-around and the departure could take 15 each. “There are many different ways to do it.”
But by the time it reached the Department of Transport, the rule had already been rewritten. In April 2023 the Minister’s officials, passing on what daa and the Aviation Authority had told them, explained it to his office: “To operate parallel runways safely, flightpaths must diverge by a minimum of 30 degrees northwest after take-off.”
Northwest. The ICAO manual has no compass in it. Somewhere between Montreal and the Minister’s office, “diverge” picked up a direction, and the direction was over towns.
And the 15? That was for both runways sending planes off at once, the busy-time capacity. When the runway opened, that was the plan: by March 2023, “Dual Departure operations from Runways 28R and 28L”. In September 2023 it was “CANCELLED WITH IMMEDIATE EFFECT”. No reason given. Nothing replaced it.
So the split the public was shown went with capacity nobody uses. The turn they got came with Heathrow’s kind of capacity, and Dublin uses less than half of it. It stayed.
Meeting the rules and doing the least harm is engineering. It starts with counting who lives under each option. Nobody did (story 3 has the four bodies we asked for it).
So, here’s where we’ve landed. A safety rule says a departure and a go-around must diverge. It doesn’t say which one turns. The rare plane that abandons a landing could do it, or the two could split it between them. The regulator says there are many ways to do it. Somewhere between Montreal and the Minister’s office, “diverge” picked up a direction: northwest. So day after day the departures do the turning, over people nobody asked, and nobody counted who lives under them. And the capacity the two splits are for? Planes off both runways at once, the airport doesn’t use at all. Landing on one and taking off from the other, it uses less than half of.
See the pictures: What is a missed approach?, It’s a Safety Requirement and Motorway in the Sky.
Sources
- International Civil Aviation Organization (ICAO), Manual on Simultaneous Operations on Parallel or Near-Parallel Instrument Runways (SOIR), Doc 9643, Second Edition, 2020: Chapter 3 (independent departures, tracks to diverge by at least 15 degrees “immediately after take-off”) and Chapter 4 (segregated operations, a departure track to diverge by at least 30 degrees from the missed approach track of the adjacent approach); the First Edition, 2004, has the same two provisions. Available from ICAO by title
- daa, public consultation “Consultation on Flight Paths and Change to Permitted Operations”, display panels and brochure, October 2016 (15 degrees “approximately one nautical mile after take-off”; maps illustrated at 15 degrees “as this is the minimum requirement”). Reproduced in Appendices A and B of daa’s report on the consultation, February 2017: https://www.dublinairport.com/docs/default-source/north-runway-downloads/public-consultation-report–flight-paths-and-change-to-permitted-operations.pdf?sfvrsn=b06d628_2
- Bickerdike Allen Partners for daa, Dublin Airport North Runway: Investigation into Noise Impact of Potential Departure Routes, report A9843-R04-DC Final, 12 July 2017 (the Aviation Authority’s requirement of 15 degrees or more; the turn at about 1 nautical mile, “considered the earliest point that a turn is likely to be possible”). Released to NRTG under AIE request 2615 (daa), on internal review, 7 August 2026
- AIP Ireland (published by the Irish Aviation Authority, now by AirNav Ireland), Dublin Airport Runway 28R standard instrument departure charts, EIDW AD 2.24-13.1, as published for the North Runway’s opening in August 2022 (turns of 30 degrees, and about 75 degrees on some routes, from the end of the runway) and as revised in 2023. Current edition: https://www.airnav.ie/air-traffic-management/aeronautical-information-management/aip-package; NRTG holds copies of the 2022 and 2023 editions
- Irish Aviation Authority, letter to the Joint Committee on Transport and Communications, “Flightpaths at Dublin Airport”, 7 November 2023 (“In principle, the missed approach procedure for 28L could turn left …”). NRTG holds a copy
- Joint Committee on Transport, evidence of the Irish Aviation Authority, 24 March 2026 (“There are many different ways to do it”). Official report: https://www.oireachtas.ie/en/debates/debate/joint_committee_on_transport/2026-03-24/
- Department of Transport, email from officials to the Minister’s office, 26 April 2023, relaying information provided by daa and the Irish Aviation Authority (“flightpaths must diverge by a minimum of 30 degrees northwest after take-off”). Released to NRTG under FOI request FOI-2025-0110 (Department of Transport), 24 July 2025