CAA points the way to interim solution on Route 4

The CAA have published a letter to Gatwick suggesting the way to an interim solution on Route 4. This follows the successful conclusion of Plane Justice’s judicial review claim in January, which saw the CAA concede the case on all grounds.

This interim solution would focus on conventional navigation prior to November 2013 (i.e. pre-RNAV). As the CAA have observed in their letter, the pre-RNAV conventional route over ground can be updated (see note 1 below), and with goodwill and good faith on all sides this would open the way for all commercial aircraft on Route 4 to fly in their historical location, before the RNAV changes introduced in 2013.

This may not mean aircraft would return to flying using ground-based conventional navigation, but would instead adopt a sat-nav emulation of conventional navigation known as a ‘coded overlay’ (see note 2 below). Coded overlays have been in use at Gatwick for a number of years now.

Whether true conventional or coded overlay technology is deployed, the CAA letter makes clear an interim solution is available which could be capable of implementation in a matter of months – one which brings into much earlier sight an end to flying an unlawfully imposed route, and honours assurances previously given.

We call on Gatwick to take the lead and begin work immediately on implementing this interim solution for all commercial aircraft using Route 4, to bring desperately-needed relief to the communities affected by the current route.


  1. On 9 February 2018 the CAA wrote to Gatwick setting out a number of practical steps they envisaged in the wake of the JR. The CAA’s letter is available here The fifth paragraph of this letter (highlighted) suggests the way to an interim solution, based on designs which track over the ground the route being flown by aircraft using conventional navigation technology in effect in 2012 (subject to taking into account any 2017 obstacle data, e.g. any new building structures, masts etc).
    (The significance of the 6th April 2017 date in the CAA’s letter, is that it takes into account the nullifying of the CAA’s decision which was made the next day; and see note 3 above).
  2. A coded overlay is a conventional instrument flight procedure which has been coded by an airline’s coding house for use by an aircraft Flight Management System (FMS) – in other words it’s a form of emulation using sat-nav. In replicating the conventional procedure design, the FMS coding can be slightly different according to airline and coding house procedures. This can result in varied track dispersion and potentially better emulation of a conventional flight pattern.