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Note: - Continued development within ICAO of the concept of navigation performance specifications is leading to the future replacement of the current system of RNP with a “Performance Based Navigation (PBN)” philosophy. Within this new philosophy, navigation specifications not requiring automatic monitoring and alerting will be known as RNAV. Navigation specifications which do require monitoring and alerting will be known as RNP. With current technology, on-board performance monitoring can only be carried out by aircraft fitted with GPS. Hence, GPS will be mandatory for RNP airspace. MNPS airspace navigation does not require an on-board automatic monitoring and alerting function. Instead pilots must remain vigilant and employ rigorous routine manual monitoring procedures.
8.1.3 MNPS was devised and implemented in the NAT Region long before the RNP concept was developed. MNPS was established primarily with the NAT OTS environment in mind. The defining waypoints of OTS tracks are specified by whole degrees of latitude and, using an effective 60 NM lateral separation standard, most adjacent tracks are separated by only one degree of latitude at each ten-degree meridian. The traffic density in the OTS is higher than in any other oceanic airspace. In such a densely populated flexible track system (one that changes twice every day), it is essential that crews avoid (whole degree) waypoint insertion errors. Such errors in the NAT MNPSA will inevitably result in a conflict with traffic on an adjacent track. For this reason Minimum Navigation Performance Specifications had to include not just the technical navigation accuracy of the Long-range Navigation Systems used on the aircraft but also the crew navigation procedures employed. The MNPS statement thus involves both cockpit/flight deck procedures and crew training requirements. In the early days of the RNP concept, it was these additional requirements that separated MNPS from RNP. However, RNP has come a long way since its inception and the development of the RNP-10 approvals for PAC operations have brought it much closer to the original MNPS concept. The ICAO Air Navigation Plan for the North Atlantic Region states that the intention in the future is that navigational performance is expected to be tied to a level of RNP. This will probably require the carriage of dual GPS to allow the required on-board performance monitoring and alerting which would be necessary for the closer track spacing then envisaged.
NORTH ATLANTIC MNPSA OPERATIONS MANUAL CHAPTER 8
NAT MNPS 41 Edition 2009
(For more detailed information on RNP and MNPS see the following ICAO Documents: Doc 9613 – „Performance Based Navigation Manual‟ and NAT Doc 001 – „Consolidated Guidance and Information Material concerning Air Navigation in the North Atlantic Region (available at http://www.nat-pco.org /.)
8.1.4 Obviously, there are several combinations of airborne sensors, receivers, computers with navigation data bases and displays which are capable of producing like accuracies, and which with inputs to automatic flight control systems provide track guidance. However, regardless of how sophisticated or mature a system is, it is still essential that stringent navigation and cross checking procedures are maintained if Gross Navigation Errors (GNEs) are to be avoided. A GNE within NAT Airspace is defined as a deviation from cleared track of 25 NM or more. Some of these errors are detected by means of long range radars as aircraft leave oceanic airspace. Other such errors may also be identified through the scrutiny of routine position reports from aircraft.
8.1.5 All reported navigation errors in North Atlantic airspace are thoroughly investigated. Records show that navigation equipment or system technical failures are now fortunately rare. However, when they do occur they can be subtle or progressive, resulting in a gradual and perhaps not immediately discernible degradation of performance. Chapter 11 of this Manual provides guidance on detection and recovery when such problems are encountered.
8.1.6 Unfortunately, human failings produce the vast majority of navigation errors in the North Atlantic Region. As indicated above, while the flexible OTS structure and the employment of a 60 NM lateral separation standard, provide for highly efficient use of NAT airspace, they also bring with them a demand for strictly disciplined navigation procedures. About half of NAT flights route via an OTS track and a large portion of the remaining random flights follow routes that at some point approach within one or two degrees of the outermost OTS tracks. One consequence of this is that a single digit error in the latitude of one significant point of an aircraft‟s route definition will very likely lead to a conflict with another aircraft which is routing correctly via the resulting common significant point. Ironically, the risk of an actual collision between two aircraft routing via a common point, as is the case when such errors are made, is further exacerbated by the improved technical accuracy of the modern navigation equipment employed.
　
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