World Air Ops | NAT | Doc 007 MNPS Guidance

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Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 8CHAPTER 8:MNPS FLIGHT OPERATION & NAVIGATION PROCEDURES8.1 INTRODUCTION8.1.1 The aircraft navigation systems necessary for flying in NAT MNPS Airspace are capable ofhigh-performance standards. However, it is essential that stringent cross-checking procedures are employed,both to ensure that these systems perform to their full capabilities and to minimise the consequences ofequipment failures and possible human errors.8.1.2 Navigation systems are continually evolving and early editions of the NAT MNPSAOperations Manual concentrated on offering specific guidance on the use of individual approved long rangenavigation systems. The current philosophy within ICAO is to specify the navigation system performancerequired for operations within a given airspace. This concept is referred to as “Performance BasedNavigation” (PBN). Within this philosophy some navigation specifications, in addition to stating theaccuracies to be achieved, also require on-board automatic integrity monitoring and alerting functions. Suchspecifications are referred to as RNP-X, where X represents an accuracy of 95% containment in X Nms.However, specifications requiring the same accuracies but not requiring on-board monitoring are referred toas RNAV-X.8.1.3 MNPS has been in use in the NAT Region for more than thirty years. It does not require onboardautomatic monitoring and alerting functions. Instead, pilots must remain vigilant and are required toemploy rigorous routine manual monitoring procedures. In the 1990’s a navigation requirements system wasintroduced for use originally in the Pacific Region. Like the MNPS, it too does not include any requirementfor on-board automatic monitoring. Its introduction was long before the PBN concept was developed and itwas then annotated as “RNP-10”. Large numbers of aircraft worldwide are now in receipt of “RNP-10”approvals. To conform with the PBN standard terminology, as indicated above, this system should actuallybe designated as “RNAV-10”. However, it has been recognised that re-classifying such a widespreadexisting approval designation would create significant difficulties for both operators and State regulators.Consequently, it has been agreed that this designation of “RNP-10” will remain as such, even though thenavigation specifications here are, in PBN terminology, effectively “RNAV-10”.8.1.4 With current technology, on-board automatic performance monitoring can only be carriedout using GPS. Hence GPS is mandatory for true RNP airspace (e.g. RNP-4) but is not required for RNAVairspace, including that historically and still designated as “RNP-10”.8.1.5 MNPS was established primarily with the NAT OTS environment in mind. The definingwaypoints of OTS tracks are specified by whole degrees of latitude and, using an effective 60 NM lateralseparation standard, most adjacent tracks are separated by only one degree of latitude at each ten-degreemeridian. The traffic density in the OTS is higher than in any other oceanic airspace. In such a denselypopulated flexible track system (one that changes twice every day), it is essential that crews avoid (wholedegree) waypoint insertion errors. Such errors in the NAT MNPSA will inevitably result in a conflict withtraffic on an adjacent track. For this reason Minimum Navigation Performance Specifications had to includenot just the technical navigation accuracy of the Long-range Navigation Systems used on the aircraft but alsothe crew navigation procedures employed. The MNPS statement thus involves both cockpit/flight deckprocedures and crew training requirements. In the early days of the RNP concept, it was these additionalrequirements that separated MNPS from RNP. However, RNP has come a long way since its inception andthe development of the RNP-10 approvals for PAC operations brought it much closer to the original MNPSconcept. The ICAO Air Navigation Plan for the North Atlantic Region states that the intention in the futureis that navigational performance is expected to be tied to a level of RNP. This will probably require theNAT Doc 007 44 Edition 2010
Guidance concerning Air Navigation in and above the NAT MNPSA CHAPTER 8carriage of dual GPS to allow the required on-board performance monitoring and alerting which would benecessary for the closer track spacing then envisaged.Note: For more detailed information on RNP see ICAO Document Doc 9613 – ‘PerformanceBased Navigation Manual’8.1.6 Obviously, there are several combinations of airborne sensors, receivers, computers withnavigation data bases and displays which are capable of producing like accuracies, and which with inputs toautomatic flight control systems provide track guidance. However, regardless of how sophisticated ormature a system is, it is still essential that stringent navigation and cross checking procedures are maintainedif Gross Navigation Errors (GNEs) are to be avoided. A GNE within NAT Airspace is defined as a deviationfrom cleared track of 25 NM or more. Some of these errors are detected by means of long range radars asaircraft leave oceanic airspace. Other such errors may also be identified through the scrutiny of routineposition reports from aircraft.8.1.7 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 immediatelydiscernible degradation of performance. Chapter 11 of this Manual provides guidance on detection andrecovery when such problems are encountered.8.1.8 Unfortunately, human failings produce the vast majority of navigation errors in the NorthAtlantic Region. As indicated above, while the flexible OTS structure and the employment of a 60 NMlateral separation standard, provide for highly efficient use of NAT airspace, they also bring with them ademand for strictly disciplined navigation procedures. About half of NAT flights route via an OTS track anda large portion of the remaining random flights follow routes that at some point approach within one or twodegrees of the outermost OTS tracks. One consequence of this is that a single digit error in the latitude ofone significant point of an aircraft’s route definition will very likely lead to a conflict with another aircraftwhich is routing correctly via the resulting common significant point. Ironically, the risk of an actualcollision between two aircraft routing via a common point, as is the case when such errors are made, isfurther exacerbated by the improved technical accuracy of the modern navigation equipment employed.8.1.9 Today in North Atlantic operations the predominant source of aircraft positioninginformation is that of GPS. This includes aircraft that use stand-alone GPS equipment and aircraft whereGPS positioning information is integrated into the system navigation solution (e.g. a GPS / IRS mix). Theaccuracy of GPS navigation is such that the actual flight paths of any two GPS equipped aircraft navigatingto a common point will almost certainly pass that point within less than a wingspan of each other. Given thatthe North Atlantic is the most heavily used oceanic airspace anywhere in the world, it must therefore beappreciated that even a single digit error in just one waypoint can result in a significant conflict potential.8.1.10 The importance of employing strict navigation system operating procedures designed toavoid the insertion of wrong waypoints or misunderstandings between pilots and ATC over cleared routescannot be over-emphasised. The principles embodied in many of the procedures described in this Chapterare aimed squarely at the prevention of such problems.8.1.11 Many of the procedures listed in this Chapter are not equipment specific and others may notbe pertinent to every aircraft. For specific equipment, reference should be made to Manufacturers' andoperators' handbooks and manuals.8.1.12 There are various references in this material to two pilots; however when carried, a thirdcrew member should be involved in all cross check procedures to the extent practicable.NAT Doc 007 45 Edition 2010
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