Route 4 historical information

Here we explain about the historical changes that have been made to Route 4 over the years. At the bottom of this page, there is a graphic which illustrates the changes to the departure track density from 1996 to 2017.

New global mapping system introduced (1999)

To prevent positioning errors and to improve consistency between different countries’ air traffic control systems, a single global mapping standard for navigating and tracking aircraft was adopted in 1999, using the World Geodetic System (WGS), the reference system used for GPS.

Locally, following the introduction of this new navigation system an anomaly was introduced that shifted the Route 4 Standard Instrument Departure route and altered the track of aircraft north of the legally defined Noise Preferential Route (NPR) (See Summer 2000 in animation below).

Correction 1 – December 1999

Later in 1999 an anomaly was identified in that aircraft were no longer able to fly over ACORN - a waypoint point built into the design of Route 4 which aircrews are required to advise ATC when passing over. In order to correct the error the position of the ACORN waypoint was moved north in December 1999; it was not recorded whether this change was instigated by NATS, BAA or the CAA.

This remedy however failed to address the issue with the change in the easterly track moving north of the NPR. The CAA has not been able to find any information on the thinking or process behind the shift north of the ACORN waypoint.

Fundamentally these historical events coming to light was the reason why the CAA decided to have their 2017 Route 4 decision quashed. 

Introducing new satellite-based navigation (2014 to 2015)

In 2014 new navigation (RNAV) routes were introduced that, because of the design criteria employed, led to a concentration of flight paths, in contrast to the more dispersed flight paths that led from conventional navigation. 

Furthermore the RNAV design criteria used at the time dictated that aircraft taking off on Route 4 make the tightest possible right hand turn which compounded the error as these concentrated flight paths were north – and just outside the NPR – so that new communities were impacted by an increase in overflight and noise (See Summer 2014 in animation below). 

Correction 2 – traffic moved back into the NPR (2015 to present day)

The situation was corrected (See summer 2016 of animation above/ below) – in that the majority of aircraft now flew the track of the Noise Preferential Route – however communities living under this flight path had become used to less aircraft noise over the last 10 to 15 years, and had never experienced overflight at the concentrated levels that the new satellite-based navigation delivered.

The CAA ratified this route following their Post Implementation Review (PIR) in April 2017, but following an application for a judicial review of its decision by a local action group, Plane Justice, and the coming to light of the pre-1999 events the CAA agreed to a court order quashing their PIR decision in January 2018.

As such, Route 4 RNAV Standard Instrument Departure routes remain in place but are subject to review as was the case prior to the CAA’s decision in April 2017.Route 4Next steps

Gatwick will continue to follow CAA guidance through this process and will work closely with them. The airport is focused on following the correct procedure to achieve an end result as soon as possible. This required rigorous legal process does however mean that a final outcome is likely to take up to two years to achieve.

Gatwick will be developing an airspace change proposal for the redesign of Route 4 in due course and we will consult widely so communities will have the opportunity to contribute and influence the eventual outcome.