PR NAV FAQs
The following are a number of questions raised so far by respondents to our consultation on the proposed implementation of nine departure routes, which replicate current (ground based navigation beacon defined) routes, using a new ‘P-RNAV’ global positioning system standard of navigation.
1. What is P-RNAV?
RNAV (Area Navigation) is the ability of an aircraft’s Flight Management System (FMS) to navigate by means of waypoints defined by latitude and longitude, rather than by conventional ground based navigational aids. Basic Area Navigation (B-RNAV – navigational accuracy ± 5 nautical miles) capability is mandated in UK controlled airspace.
Airline operators are eager for the potential advantages offered by existing equipment to be fully utilised. It is anticipated that the deployment of RNAV will realise a number of operational benefits. These will be dependent upon the type of RNAV application and the target environment. Potential generic benefits include reduced controller and pilot workload, improved situational awareness, noise reduction, reduced emissions, fuel savings and decreased engine maintenance costs.
The Precision Area Navigation (P-RNAV) standard is intended for use in terminal airspace (around airports) and requires that an aircraft is capable of a track-keeping accuracy of ±1 nautical miles for 95% of its flight time.
CAA policy is that Precision Area Navigation (P-RNAV) should be the standard applied in terminal airspace, and in accordance with this, P-RNAV capability is expected to be mandated in the future for flight in the London Terminal Airspace (LTMA) and conventional navigation procedures (including SIDs) will be withdrawn from around 2018 onwards.
2. Why do we want P-RNAV?
The CAA’s policy on future airspace strategy requires the use of P-RNAV and Gatwick is intending to be at the forefront of this changeover to more modern and accurate standard of navigation. Our proposal to implement P-RNAV standard on a gradual basis, rather than in one single withdrawal of conventional routes and replacement with P-RNAV standard, has been agreed with CAA as acceptable as we are early adopters of this policy. The gradual migration over to P-RNAV standard at Gatwick is aimed at making the impact of the change in concentration a similarly gradual one with the establishment of an ongoing review process.
Implementation of P-RNAV standard of navigation does NOT provide any additional increase runway capacity at Gatwick. Hence the proposed change to P-RNAV would not change the number of flights arriving at and departing from Gatwick.
In future, it may be possible to design P-RNAV routes using the increased accuracy of the flight profile and resultant narrower swathes of departure tracks to improve the avoidance of centres of population to greater effect than that achieved by the current NPRs.
3. How are we consulting?
Gatwick has been running a P-RNAV trial for several years in order to gain operational data to enable the CAA to make a decision as to whether this type of advanced navigation is operationally possible at Gatwick using existing noise preferential routes through replication of existing standard instrument departure routes (SIDs). This trial is due to come to an end on 20 April 2013. We are consulting with affected local Communities over a 12 week period; this began on 19 July 2012. The date for acceptance for feedback from the public has now been extended to 12 November 2012.
The purpose of this consultation is to allow stakeholders to provide feedback on these proposals to convert extant SIDs to the P-RNAV standard. There is no proposal to change any existing controlled airspace boundaries (see Q8 below).
There is no proposal to change air traffic control practices (see Q 9), only the method by which certain procedures (SIDs) are defined within the UKs Aeronautical Information Publications (AIP) and the on board navigation system of aircraft operating from Gatwick. Subject to the consultation process following submission of an airspace change proposal to the CA, and subsequent regulatory approval, the P-RNAV SID procedures will be implemented in parallel with current conventional SID procedures from Gatwick and a continual review process, agreed from the feedback of this consultation, will be followed with the aim to withdraw conventional SIDs within five years of implementation.
This consultation is being progressed in line with CAA guidance on the process for airspace change as detailed in their CAP725 document, and with reference to agreed process requirements established through briefings on the development to the CAA.
4. How will P-RNAV be implemented?
The current P-RNAV trial has been conducted on four of the airport’s existing noise preferential routes (NPRs) and was run with aircraft crews making the final decision as to whether or not they fly a P-RNAV route. If P-RNAV is granted approval by the CAA then again it will be the decision of the aircraft crew as to whether a P-RNAV departure route is followed, however it is expected that as this will not be under trial circumstances, these types of departures will become more common and that over a period of up to five years following implementation, all aircraft at Gatwick will use this technique.
During this time if the change to P-RNAV navigation causes significant change in the noise impacts on the local community, then the fall back position is to withdraw the P-RNAV route and return to the conventional SID while the P-RNAV SID is redesigned/consulted.
5. How will the proposed P-RNAV routes affect me?
We have created a series of detailed maps to illustrate the centreline of current departure routes (SIDs) and how the tracks of aircraft flying on these SIDs are concentrated over the ground. We have also provided the same map information to show the centrelines of each proposed permanent P-RNAV defined route in relation to the centreline of the conventional route on which it is based, so that they can be seen in relation to locations on the ground.
Four of the proposed routes have already been flown under trial and for these routes (route 1, 2, 3, and 4) we have also provided information on the maps as to how the tracks of aircraft flying on these P-RNAV defined routes have been concentrated over the ground. These maps can be viewed and downloaded here.
6. Who are we consulting with?
In developing our consultation process we have ensured that the CAA and NATS have been involved. It was agreed with the CAA that the consultation would be launched through the Gatwick Airport consultative committee GATCOM, which was done on 19 July 2012. We agreed with the CAA that all affected communities and pressure groups would be represented by the current GATCOM membership. However, in order to ensure everybody was aware of the consultation, the airport has also written to all surrounding local authorities and parish councils. GATCOM will be presenting a GATCOM response to the consultation but this does not preclude GATCOM members or groups they represent from responding separately.
The consultation is available here and on GATCOM’s website. We have also issued a news alert to all local media outlining the consultation process and the deadlines for feedback. We are also presenting P-RNAV to communities around the airport in order for people to have the opportunity to ask questions and seek clarification. We plan to visit Dormansland Parish Council, Leigh Parish Council and Capel Parish Council.
7. How can I be sure that Gatwick has followed the correct consultation process and is adhering to the CAA’s guidance on the application of the airspace change process?
The CAA guidance document CAP725 is primarily concerned with the content of final Airspace Change Proposal (ACP) submission that must be made to the CAA’s Directorate of Airspace Policy (DAP) eg statements of what a submission MUST be included relate to the ACP not to the consultation document. The required contents of the consultation material and ACP was agreed with the CAA. Every ACP is different and the DAP treats each on a case-by-case basis. As such CAP725 requirements can be waived subject to agreement by the DAP. This is recorded formally in the framework briefing record of agreement and is subject to final review by CAA (DAP) when the ACP submission is made to them by Gatwick Airport Ltd. The submission will include all responses received from individuals or groups as part of the consultation.
Should you believe that the correct process has not been followed, you may raise this directly with CAA at the following address:
Business Coordinator Directorate of Airspace Policy
CAA House, 45-59 Kingsway London, WC2B 6TE
This address is also included at the foot of our P-RNAV consultation response form
8. If P-RNAV based procedures lead to a significant narrowing/concentration of flight paths, albeit within the boundaries of existing NPRs, isn’t this a change to existing airspace boundaries?
There is no proposal to change the boundaries of any airspace. All airspace is classified according to ICAO airspace Classes. The airspace around Gatwick is classified as Class D from the surface to 2500ft and Class A above 2500ft. All of the extant and proposed SIDs in question are contained within the existing controlled airspace, and no boundaries of this airspace are proposed to change. 9. If a new standard of navigation (P-RNAV) is being used to replicate current routes, isn’t this a change to existing air traffic control practices? Air traffic control and the airline pilots they work with will continue to use exactly the same procedures and ATC practices. The CAA Aircraft Navigation Capability Survey undertaken in 2011 indicated that approximately 95% of airframes operating from Gatwick are RNAV1 (P-RNAV) equipped. Hence the majority of aircraft are already equipped to fly P-RNAV procedures, and many of them are currently flying conventional SIDs using P-RNAV equipment, to P-RNAV performance tolerances. The proposed subtle change in the definition of SIDs enables these aircraft to make best use of the sophisticated navigation equipment that they are fitted with. It does not constitute a change to air traffic control procedures or practices.