New Southern Sky and Performance Based Navigation
The introduction of navigation procedures that use accurate data from the Global Network of Satellite Systems (GNSS) will mean shorter, more direct flights.
What is performance based navigation and why is it different?
Air Navigation involves planning, directing and monitoring the movement of an aircraft from point of departure to destination. Today most operations under Instrument Flight Rules (IFR) use a network of land-based aids to navigate along fixed routes and to conduct instrument approaches and departures from aerodromes.
Performance Based Navigation (PBN) is a globally recognised term for navigation procedures that rely on GNSS equipment meeting specific performance standards. These standards are required because some systems do not provide sufficient accuracy, integrity, continuity or functionality to ensure flight safety in a PBN environment. PBN route, departure and arrival procedures enable more accurate navigation than those utilising traditional ground-based navigation aids, such as VORs and NDBs, and allow for shorter, more direct flights as well as for flexible routing. Aircraft equipped with GNSS receivers can identify their positions accurately at every point along their journey, and this means greater flexibility during flight.
PBN will become the primary method for IFR flight in the future. New Southern Sky is deveoping required performance specifications for GNSS equipment, so that IFR operations can realise the potential of PBN. To make a safe transition to the PBN environment, operators will need to ensure that their equipment, procedures and training meet acceptable standards. These standards will be further developed in rules and guidance.
PBN routes are expected to reduce emissions, with less fuel burn and fewer carbon emissions. Widespread change to air navigation routes, approaches and departures may result in changes to overall noise patterns resulting from more accurate tracks over particular areas. This is most likely to affect areas close to aerodromes with more accurate flight paths. New Southern Sky supports Airways NZ and airport companies’ engagement with their communities on the implications of PBN for them.
The Global Navigation Satellite Systems Sole Means Recommendation Report considers the role of GNSS here in New Zealand.
Current Technologies - What do we already know?
There are two types of PBN performance specifications:
- RNAV (aRea NAVigation) A method of navigation that permits aircraft operation on any desired flight path within the coverage of ground or satellite-based navigation aids or within the limits of the capability of self-contained aids, or a combination of these. RNAV is a navigation specification designation that does not include requirements for on-board performance monitoring and alerting.
- RNP (Required Navigation Performance) allows an aircraft to fly a specific path between two points in space that are defined in three dimensions. RNP is a navigation specification designation that includes requirements for on-board performance monitoring and alerting. This notifies a pilot of any reduced satellite integrity – making for a more robust system. For example, GNSS with Receiver Autonomous Integrity Monitoring (RAIM) meets the required standards.
RNAV instrument approach procedures can be augmented with lateral and vertical guidance called Approach Procedures with Vertical guidance (APV). These do not meet the requirements established for precision approach and landing operations.
The following diagram illustrates the ICAO RNP and RNAV specifications:
ICAO Navigation Specifications
How accurate is area navigation (RNAV) and required navigation performance (RNP)?
RNAV and RNP generally mandates a certain level of equipment and assumes you have a 95% chance of keeping to a stated level of navigation accuracy. RNAV 1 and RNP 1 both say you have a 0.95 probability of staying within 1 nm of course. RNP will let you know when the probability of you staying within 2 nm of that position goes below 0.99999 (on-board alerting).
Therefore, RNAV 2 and RNP 2 both say you have a 0.95 probability of staying within 2 nm of course, and so on.
Upgrade costs and practicality
Aircraft operating in New Zealand airspace currently have a diverse range of navigational capabilities. This diversity, coupled with a wide mix of aviation activities, a high level of non-commercial operations and an older aircraft fleet, mean that not all operators will be equipped to meet future requirements and the cost of upgrading will vary.
To ensure an effective transition to the PBN environment, New Southern Sky will:
- Encourage early uptake of the technology.
- Ensure that there is sufficient time allowed for aircraft to be equipped, and operators, pilots and air traffic controllers to be trained in the new modes of navigation.
- Collaborate with instrument procedure design organisations, aircraft aerodrome operators and affected communities to ensure a smooth transition.
- Accommodate mixed-equipage operations until a full PBN environment is in place.
- Ensure implementation of the navigation portion of the CNS/ATM system is capable of supporting the operational airspace concept.
- Limit the number of equipment types required in aircraft and on the ground to reduce costs.
Aviation navigation today
In 1997, New Zealand was one of the first countries in the world to implement rules to allow instrument flight procedure operations using GNSS. These rules need to be updated to reflect the modern use of navigation using GNSS, and PBN in particular.
In 2009, ICAO resolved that all States should develop a PBN Implementation Plan. In response New Zealand published its PBN Implementation Plan. It was one of the first to be produced and was internationally recognised as a model for others to follow.
The agreed concepts for New Zealand continue to be implemented through a three-phase process with target implementation dates of 2017 and 2020. Through this process, all Air Traffic Service routes (including Standard Instrument Departures–SIDs and Standard Arrival Routes–STARs) will be enabled by RNAV (or RNP where required). All runway ends with instrument approach procedures will be enabled by RNP.
The Plan adopted the following standards for New Zealand domestic PBN:
- RNAV 2 for en-route operations.
- RNAV 1 for all terminal routes with surveillance services and Basic RNP 1 for routes without surveillance services.
For approach operations – RNP APCH. The legacy RNAV (GNSS) arrivals, RNAV (GNSS) SIDs, and RNAV (GNSS) approach procedures currently used in New Zealand are being replaced with the above specifications as they are reviewed.
As a result of this early planning, design and implementation of RNAV routes and procedures is well advanced. Existing ground-based navigation aids remain in operation and operators currently have a choice between the existing navigation systems and PBN procedures in many parts of the country.
The following procedures are already promulgated:
- RNP 10 (RNAV 10) and RNP 4 in Auckland Oceanic airspace.
- All domestic RNAV Air Traffic Service (ATS) routes were designated RNAV 2 on 15 November 2012.
- Arrival and departure procedures.
- RNAV (GNSS) approach procedures at most aerodromes to replace or complement existing ground-based instrument procedures.
- RNAV (GNSS) arrival and departure procedures (RNP 1 application) at selected regional aerodromes.
- Approach with vertical guidance based on Barometric Vertical Navigation (Baro-VNAV) criteria at all international airports.
- RNAV Standard Instrument Departure Routes (SIDs) and Standard Arrival Routes (STARs) being implemented at Auckland, Wellington, and Christchurch aerodromes.
- RNP AR APCH procedures at selected terrain challenged locations e.g. Queenstown and Rotorua.
New Southern Sky will make changes to the regulatory framework to streamline the process for approvals. These will include an amendment to AC 91-21 and a new Rule. The CAA’s current regulatory framework for PBN equipment and operations comprises:
- Civil Aviation Rule 91.501(2)
- Civil Aviation Rule 91.519
- Civil Aviation Rule 121.353
- Civil Aviation Rule 125.353
- Civil Aviation Rule 135.353
- Civil Aviation Rule 19 (Sub-part D)
- Advisory Circular AC 91-21, Rev 0.3 PBN (Operational Approvals)
Operators must gain approvals for all PBN navigation equipment and procedures:
- Maintenance procedures (including navigation database maintenance)
- Pre-flight planning requirements
- General operating procedures
- Contingency procedures
- Training requirements
- Airworthiness approvals
Pilots may conduct PBN operations only if they have an appropriate instrument rating for the navigation system and meet the currency requirement.
Airways has a PBN implementation plan for all controlled aerodromes. It is scheduled for completion in 2017 and includes instrument procedure design and associated air traffic controller training.
Some large operators, including Air New Zealand, have also developed their own PBN implementation plans.
The New Southern Sky Safety Group ensures that all safety issues related to bringing in new procedures are addressed from a systems perspective.
It will focus on ensuring:
- Operators wishing to use the new routes have certainty about expectations and the equipment capabilities, operational procedures and training to manage the new routes.
- PBN is effectively implemented into the air traffic management system.
- Navigation databases are accurate, reliable, and from an approved provider using approved data transfer protocols.
- Meteorological information supports PBN use.
Reliability of the satellite navigation system – contingency
New Southern Sky will ensure:
- At least one ground based instrument approach procedure is retained for each main runway end at controlled aerodromes.
- A ground-based navigation aid contingency system is in place so that in the event of a GNSS outage, all airborne aircraft can land safely, and that service can be continued on the main trunk routes.
- Instrument landing systems will be retained at international airports and their alternates.
PBN routes are expected to reduce emissions, with less fuel burn and fewer carbon emissions. Widespread change to air navigation routes, approaches and departures may result in changes to overall noise patterns resulting from more accurate tracks over particular areas. This is most likely to affect areas close to aerodromes with more accurate arrival and departure flight paths. When dealing with the potential impact of aircraft noise, New Southern Sky will take note of the provisions of the ICAO Standards and Recommended Procedures for Environmental Protection – Aircraft Noise, Annex 16, Volume 1.
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