NAVAID rationalisation

Heathrow, like most UK airports, has traditionally relied upon ground-based navigational aids (or ‘beacons’) to direct aircraft. These aeronautical beacons are located at sites around the UK, including at some airports, and provide radio signals to aircraft as reference points for arrival, departure and en-route procedures. However, they use old technology and are coming to the end of their serviceable life. NATS En-Route (NERL), as the provider of air traffic control services for aircraft flying ‘en-route’ in UK airspace, is leading a UK-wide programme to remove the beacons, known as NAVAID Rationalisation.

Aircraft arriving and departing Heathrow do not currently use these ground-based navigational aids, and instead rely upon coded “overlays” within the aircraft’s Flight Management System (FMS). These overlays are designed to replicate the same track over the ground the aircraft would have taken if it relied on the beacons. Instead of using information gleaned from the beacons, GPS waypoints are coded into the aircraft’s FMS and this method of navigation is known as Area Navigation or “RNAV”. Aircraft have been using this method of navigation for many years across the UK, including at Heathrow, and NERL’s rationalisation programme requires Heathrow to now formalise the use of RNAV overlays.

To formalise the use of RNAV overlays, airports are required to submit an Airspace Change Proposal (ACP) under the CAA’s formal airspace change process, known as CAP1616. Our ACP will not change the routes used by arriving or departing traffic at Heathrow.

This new ACP is separate to our current airspace change proposal for airspace modernisation at Heathrow, and our intention is that the formalised RNAV overlays will be introduced as a temporary measure ahead of the more significant changes envisaged under our Airspace Modernisation Programme.

Further information is available in the CAA’s Guidance for the use of RNAV Substitution (CAP1781).