Project AS 08/12 - Amendments to MOS Part 172 and legislative instruments under CAR 174A and 179A
The parameters used by ATC for separation based on Global Navigation Satellite System (GNSS) position are quite conservative when compared to the demonstrated accuracy and reliability of GNSS in flight operations. For instance, a tolerance of 14NM (26km) must be applied to the reported GNSS position, and separation is then based on the extremities of this circular tolerance area (known as Circular Error of Position [CEP]). Accordingly, for two (2) aircraft reporting position via GNSS, minimum lateral separation must be the sum of the both aircraft's CEP plus a buffer factor of 1NM (1.8), giving a lateral separation minimum of 29NM (54km). Simply put, two aircraft at the same cruising level will only achieve minimum lateral separation if they are flying on different air routes spaced at least 29NM (54km) apart.
This lateral spacing requirement severely limits the options for efficient and fail-tolerant route structures between airports, particularly in the more remote areas of Australia that are not well provided with traditional navigation aides (VHF Omni Range, non-directional beacon etc) and which are outside of radar surveillance coverage. One area so affected is regional Western Australia. Airservices Australia has conducted a series of reviews into the airspace and air route structure in Western Australia, and has identified the need for comprehensive changes to the air route structure in order for the system to better cope with current and projected traffic levels.
The proposed changes to the Western Australia air route structure are based in part on research, conducted both in Australia and the international aviation community, which has determined it is possible to reduce the current 14 NM CEP value to 7NM, whilst maintaining an adequate level of safety. The International Civil Aviation Organization (ICAO) is in the process of adopting the revised CEP value into the manual of international standards for air traffic control (ICAO Procedures for Air Navigation Services - Air Traffic Management [PANS-ATM] Document 4444).
However, due in part to the requirement for ICAO to consult with all 190 contracting states, the process for amending the PANS-ATM will take at least two (2) years. The implementation date (20 November 2007) is well past the point at which revisions to the Western Australian airspace structure need to be in place.
Airservices Australia has already conducted extensive risk assessment and industry consultation on both the airspace/air route changes and the revised CEP standard. The only limiting factor at this point is the absence of a relevant CEP standard from either international standards or CASA regulatory standards (normally contained within the Manual of Standards [MOS] Part 172).
Accordingly, to permit the implementation of the revised Western Australia airspace structure within project timelines, it is necessary for Australia to introduce the revised GNSS CEP value in advance of ICAO. To enable this to happen, CASA proposes changes to MOS Part 172 under the Notice of Proposed Change (NPC) process. The NPC will include the revised CEP value, and conditions for use, including a revised reporting requirement for Receiver Autonomous Integrity Monitoring (RAIM) outages, failures (from current 10 minutes to proposed 5 minutes). The proposed standards will also require amendments to Civil Aviation Advisory Publication (CAAP 179-1(1) and legislative instruments on the use of GNSS issued under Civil Aviation Regulation (CAR) 1988- 174A and 179A.
To establish an Australian regulatory standard, and associated operating procedures, for a 7-nautical mile Circular of Error of Position (CEP) tolerance, based on GNSS position, to be used for ATC separation.
The project was approved by Peter Cromarty, General Manager, Airspace and Aerodrome Regulation Group on 7 August 2008.
Project Leader:Jan Goosen
RDMB Programme Manager: Andrew Ward
Project Sponsor: Peter Cromarty, General Manager, Airspace and Aerodrome Regulation Group
Standards Consultative Committee (SCC)
|Consultation updates in 2008|
Project AS 08/12.
|Amendments to MOS Part 172 were issued under CASA miscellaneous legislative instrument Manual of Standards Part 172 Amendment (No. 1) 2008. The amendments became effective on 20 November 2008.||2 Dec 2008|
|This NFC has been published.||2 Dec 2008|
|NPC 172/03 - Proposed Amendments to Manual of Standards (MOS) Part 172 - Air Traffic Service Providers and Flight crew requirements for use of Global Positioning System (GPS)||Comments to this Notice of Proposed Change (NPC) closed on 20 October 2008||18 Sep 2008|
|Project AS 08/12 - Amendments to MOS Part 172 and legislative instruments under CAR 174A and 179A||This project has been approved and information is now available.||
8 Aug 2008