Route 4 is a departure route for aircraft taking off from Gatwick toward the west. Soon after take-off aircraft wrap 180 degrees round to the right and heads east, flying close to areas of South Holmwood, Leigh, Redhill and Reigate.

The CAA decision on the Route 4 Standard Instrument Departure (SID) routes Post Implementation Review in April 2017 has been quashed by the Court at the request of the CAA. 

The process to date has been complex. Before outlining what the court action means, it is worth explaining step by step how the current situation arose and why airspace around Gatwick - including Route 4 - has been redesigned.

Why does airspace need to be redesigned?

UK airspace was originally designed over 50 years ago and current capacity is approaching its limits.  To ensure that the UK can meet future demand, the Government Future Airspace Strategy sets out a plan to modernise airspace by using modern satellite technology for air navigation, as opposed to ground-based beacon technology.   

What does this mean for Gatwick Airport?

Gatwick – and all other UK airports – have or are in the process of redesigning their departure routes to be in line with UK policy so that aircraft can use new satellite-based navigation technology.

As such, in 2013 we sought the CAA's approval to implement changes to all nine of our departure routes and these changes were approved by the CAA in August 2013, following our airspace consultation.

Post Implementation Reviews

Following CAA approval of new route designs – and after they have been flown for a period of time – the CAA performs Post Implementation Reviews of all new routes.  This is done to assess whether the anticipated impacts and benefits of the airspace changes happened in practice.

In 2015 the CAA reviewed all nine of our redesigned departure routes and approved the majority.  They did however find that Route 4 had not delivered the aim of the airspace change and required Route 4 to be modified.  Minor changes were also required to two other departure routes.

Following the CAA’s finding on the redesigned Route 4, we submitted an amended Route 4 proposal which the CAA ratified following their Post Implementation Review in April 2017.

Legal challenge

A community group – Plane Justice – however sought a judicial review that challenged the CAA’s Post Implementation Review decision to ratify the revised Route 4 departure route. 

And following ‘detailed and lengthy investigations’ the CAA asked the court to quash their previous decision which brings us up to the present day.

Why did the CAA reverse their previous decision?

The reason the CAA felt it could not allow their Post Implementation Review decision to stand was that during the process of responding to litigation the CAA discovered that the historical changes to the conventional route were not for entirely the reasons originally identified.

The formal notification issued to us by the CAA is available to read online.  The letter states that during their investigation ‘it became apparent that magnetic drift was not the predominant factor causing displacement of Route 4 from the Noise Preferential Route (NPR). The CAA considered that it could not allow its decision to stand where such decision was based upon a misunderstanding of the relevant facts.’

Because this information was not previously available to either the CAA or Gatwick, the CAA considered that we could not have conducted a proper consultation in 2016 and therefore it could not allow their decision to stand.

What is happening now? 

On 6 May 2020, the CAA published the CAP 1912 Post Implementation Review Report in which they confirmed the decision that required us to remove all temporary Route 4 satellite-based departures routes - RNAV1 Standard Instrument Departures (SIDs) - that were introduced on 26 May 2016.

Following the publication of the CAA decision, alongside our partners, we began to prepare the necessary changes for the safe withdrawal of the temporary Route 4 RNAV1 SIDs, taking into account the complexities of reverting from a more technically advanced to a legacy route structure (a revision not previously undertaken in the UK).

We met with the CAA and with the air traffic control service providers (NATS and ANSL) in July and August to provide further details on our plans to implement the requirements of CAP 1912.

The plans proposed by Gatwick, NATS and ANSL aimed to mitigate the safety and operational risks and issues identified and is described in some detail in the consolidated notes of these meetings which are available here

On 9 September 2020, the CAA wrote to us outlining their position in response to our plan.  The CAA acknowledged the increased complexity and safety risks due to changes in the route connectivity and the need for the conventional SIDs - which have been little used in recent years - to be truncated to connect seamlessly to the airways structure above southern England. The CAA also accepted that a series of airspace changes implemented over a short period of time to effect this change was not desirable due to an increased safety risk and therefore agreed to a single date on which all associated changes would be implemented.  Consequently, the implementation aimed for 25 February 2021 was agreed. The CAA's letter is available here.

All changes required by CAP 1912 and our subsequent plan were implemented successfully on 25 February 2021. 

The RNAV1 SIDs FRANE, LAM, BIG and ADMAG have been removed; the Clacton (CLN) and Dover (DVR) conventional SIDs have been truncated into FRANE and MIMFO conventional SIDs; and the changes published in the UK Aeronautical Information Publication (AIP).  All air traffic control systems and procedures have been updated successfully.

Following the removal of the RNAV1 SIDs, as per CAP 1912, airlines continue to fly Route 4 SIDs, with the track over the ground guided by a satellite-based coded overlay of the conventional SIDs.  Because coded overlays are created outside of the regulated process - and without reference to us - it is not possible to predict the variations in aircraft track that may result.  With this in mind the separation between departures using Route 4 has been temporarily increased to ensure the safe separation between departing aircraft.

In order to assess the potential hazards identified during the assessment of likely performance of aircraft flying conventional SIDs in the first turn on Route 4, we completed a period of detailed track keeping performance with ANSL to monitor  aircraft in the first turn on Route 4. ANSL is reviewing the results from the monitoring exercise. A summary of the data from the Route 4 track monitoring exercise is available here. We continue to closely monitor track performance across all our departure routes and reports track keeping performance via our quarterly and annual noise performance reports.

2018 Airspace Change Proposal - considering the implementation of Performance Based Navigation on Route 4

At that meeting, held in March 2020, the CAA explained it was not satisfied that the existing pattern of traffic - using the temporary RNAV1 routes - provided an adequate baseline or do nothing option against which to assess the proposed route options developed during stage 2 through engagement with industry and local stakeholders.

Following this, we have actively sought to address the problem of the baseline data option and engaged CAA to seek a workable solution.

In February 2021, CAA confirmed that the conventional route track, after the RNAV1 SIDs have been removed on 25 February 2021, is the appropriate route pattern to be used to determine the baseline or ‘do nothing’ option as part of this airspace change proposal.

The added difficulty was generated by the highly disruptive impact of COVID-19 on traffic patterns, both locally and Europe wide.  This meant that for the purpose of establishing a baseline, current volumes and patterns are not representative.

To address this issue, we have proposed to use the average conventional route track, post 25 February 2021 after the RNAV1 SIDs have been removed, as the route over the ground and apply the traffic volumes and SID destinations using the historical (2019) traffic volumes.  This approach would provide a more representative ‘do nothing’ option as required by the CAA airspace change process.

In October 2021, CAA reviewed and endorsed this proposal.

Given the delay created by the need to reconsider the traffic baseline and 'do nothing' options and the impact of COVID-19, our plans for progressing this airspace change have been significantly delayed. We have revised our airspace change timelines and proposed a new Stage 2 Gateway in May 2022.

You can read more about this airspace change, including a record of the meeting with the CAA on the CAA Airspace Change Portal.

Route 4 historical information