4.4 Acceptable Means of Compliance for MNPS General 4.4.1 In developing the application of the concept of MNPS, it was recognised that an indication of an "Acceptable Means of Compliance" would be needed, with specifications in terms of aircraft equipment. However, equipment specification is only one part of the total quality of performance required. Certification for operations in NAT MNPS Airspace requires a) attention to crew training and operating drills as described in the "NAT MNPS Airspace Operations Manual b) attention to equipment installation and maintenance procedures can assurance that the ICAO Annex 6 (Operation of Aircraft) requirement for navigation equipment redundancy is satisfied and d) the use of equipment that is suitable. 4.4.2 This section addresses only one of these aspects, namely the navigation equipment fits that justify consideration. 4.4.3 It is unsatisfactory for NAT MNPS Airspace operations to rely on intermittent updates of aircraft position. The standard requires for navigation equipment that continuously provides indications to the flight crew of adherence to or departure from track, to the required degree of accuracy, at any point along that track. To this end, it is highly desirable that the navigation system in use is coupled to the autopilot so that continuous steering guidance is provided. The Horizontal Navigational Performance Requirement 4.4.4 There are two navigational requirements for aircraft planning to operate in NAT MNPS Airspace. One refers to track-keeping accuracy and the other refers to standby equipment with comparable performance characteristics (ICAO Annex 6, Chapter 7 of Parts I and II, refers). To justify consideration for State approval for unrestricted operation in NAT MNPS Airspace, an aircraft needs to be
