Navigation Specification 1 Introduction

As the en-route design often involves route realignments, to maintain sensor-specific routes and procedures would be inflexible and costly. To overcome the constraining elements, reflected through the inflexibility of route alignments often caused by a current conventional navigation infrastructure, other navigation solutions should be considered. The performance based navigation, may pose either as a strong enabler, or as one of the navigation assumptions, for the airspace design solutions.

6.6.2 Navigation specifications options

The navigation specification presents a set of aircraft and crew requirements needed to support performance based navigation operations within a defined airspace.

Depending on the type of airspace, and possibly to accommodate closer route spacing, adequate navigation enablers are proposed referring to airborne navigation equipment and the Navigation Specifications prescribing their performance.

Once it is established that a certain sub-set of navigation functionalities are needed to enable an Airspace Concept and that the fleet is appropriately capable, what remains is to select a navigation specification from the PBN Manual (ICAO Doc 9613) that matches, in terms of navigation performance, the ones required for the Airspace Concept.

Selecting navigation specification is a simple step if preceding airspace design phases have been done in an integrated manner. Assumptions identification has to be done carefully when it comes to fleet analysis whilst giving due consideration to an ICAO Navigation Specification. This match could be difficult to achieve because it is seldom cost effective to select a navigation specification that would require a significant proportion of fleet to retrofit RNAV systems to provide specific functionality.

The Navigation Specification can either be RNAV or RNP. The difference between the two is that RNP specification includes a requirement for on-board, self-contained, equipment for performance monitoring and alerting.

6.6.3 Navigation functional requirements

Both specifications, RNAV and RNP, include requirements for certain navigation functionalities that should be taken into account when airspace design proposals are developed. Some of the functionalities associated to a navigation specification may influence, not only route spacing and separation minima, but the airspace concept as such. When proposing airspace design solutions, one should take into account the following set of navigation functionalities, as a minimum:

 continuous indication of aircraft position relative to track to be displayed to a pilot flying, on a navigation display;

 display of distance and bearing to the active (To) waypoint;  display of ground speed or time to the active (To) waypoint;  navigation data storage;

 appropriate failure indication of the RNAV system.

A strategic objective concerning the airspace improvements will allocate requirements to various system components, such as communication, navigation, ATS surveillance, air traffic management and flight operations. Navigation functional requirements, in the context of performance-based navigation, need to be identified.

Requirements determination

The process should start from the airspace users’ needs and consequently airspace requirements. When it comes to determining airspace users’ requirements, a balance amongst overall safety, capacity and efficiency should be established. Trade-offs between competing requirements will have to be made.

An important step towards the determination of the users’ and airspace requirements should be assessment of aircraft fleet capability. Namely, owing to the fact that some five generations of aircraft may be simultaneously using the airspace in question, the proposed airspace solutions should accommodate them all.

It is important to know the characteristics and level of equipage of the fleet operating in the airspace. Several characteristics to be observed are listed hereafter:

 aircraft equipped with GNSS capability;

 failure of GNSS could be mitigated by other means of navigation (DME based RNAV, conventional navigation, ATS surveillance);

 IFR approved aircraft carry VOR and DME integrated into RNAV system;  extent of need for aircraft inertial systems to cover potential navaids signal

gaps.

Handling traffic with mixed navigation equipage, depending on the level of mixed equipment and operations, adversely affect capacity of the airspace and place additional workload on controllers.

Navaid infrastructure assessment is also an important step since the majority of current route network is supported by ground-based navaids, Nevertheless, the use of RNAV is expanding allowing operators to take advantage of on-board systems.

A full transition to RNAV-based en-route should be considered. However, it may take years for GNSS to be used by a significant majority of operators, so ground-based navaids should be considered as an alternative input to RNAV systems, as a support to reversionary conventional navigation or even to use them for the provision of conventional navigation environment for non-RNAV-equipped users.

The following should be taken into account when assessing navaid infrastructure for the given airspace:

 rate at which operators using the airspace in question, equip with GNSS- capable avionics;

 extent of the requirement to retain some ground navaids for operators not equipped with GNSS, or as a back-up to GNSS;

 the existing navaid infrastructure and its age.

Implementation of RNAV applications must not be a cause for installing new navaid infrastructure. RNAV applications should ideally result in moving some of the existing infrastructure (DMEs removed from VORs, etc.).

6.7 Flight Procedures

6.7.1 Terrain and Obstacle Clearance

The design principles addressed in this document refer to the conceptual design of the Airspace structures (routes, holds, ATC sectorisation etc.). PANS-OPS addresses the final stage of this design process by assuring the desired structures are clear of obstacles considering the criteria in ICAO Doc 8168.

The details of Flight Procedure design in accordance with obstacle clearance criteria are outside the scope of this document. For details on the safe design of procedures with respect to terrain and obstacle clearance, refer to ICAO Doc 8168 and consult a qualified PANS-OPS designer.

In logical steps, PANS-OPS design is done after the conceptual design, assessment of the design concept, assessment of the design validation and the implementation planning. For En-route applications, PANS-OPS criteria are generally not as restrictive as in Terminal Airspace because of the higher altitudes of the route segments.

6.8 Sectorisation