A-rnp Approach

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Aug 3, 2024, 4:39:17 PM8/3/24

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Advanced Required Navigation Performance (A-RNP) is the latest navigation specification in the evolution of Performance Based Navigation (PBN). The following information is intended to provide a basic understanding of A-RNP and required aircraft capabilities.

PBN is comprised of two kinds of navigation specifications: RNAV and RNP (figure 1). The important difference between the two is that the RNP specification requires on-board performance monitoring and alerting as part of the avionics functionality. The use of RNP systems offer significant safety, operational, and efficiency benefits. While RNAV and RNP applications will co-exist for several years, a transition to RNP is being made as the proportion of aircraft equipped with RNP systems increases and the cost to transition is reduced.

A-RNP is simply a combination of several Navigation Specifications, along with additional functions described in detail further below. A-RNP encompasses all phases of flight from departure and en route to arrival and approach. The A-RNP specification is intended to provide for an internationally harmonized standard. For the operator, it provides specific criteria used to qualify for operations on RNP routes, SIDs, STARs or approaches.

A-RNP recognition is based on navigation systems meeting the performance and functional criteria for RNP-2, RNP-1 and RNP APCH to LNAV minima. Additional to the RNP requirements, AC 90-105A and ICAO PBN Doc 9613, list the following six functional capabilities that also define A-RNP eligibility.

Radius-to-fix (RF) leg capability allows for a constant radius turn starting and ending on a fix or waypoint. The FMS computes the actual flight path, providing for repeatable and predictable turn performance. RF legs are currently used in terminal and approach procedures.

RNP scalability refers to the avionics systems ability to automatically retrieve and display the required RNP value for each leg segment of a route or procedure from the navigation database. RNP values are depicted on the primary flight display and the CDI is scaled to the RNP value for the current leg. Two-dot (full scale) deflection of the CDI equals the RNP value displayed on the PFD for the current leg. RNP scalability is applicable for all SIDS, STARS, approaches and en route airways defined by an RNP requirement.

FRTs are waypoint turn transitions between en route segments using a defined radius. FRTs are like fly-by turns, but use a fixed radius track with performance boundaries, creating a predictable, repeatable path associated with RNP. The purpose is to apply closer route spacing along turns on airways, or to transition from one airway to another.

TOAC is an advanced function of the FMS designed to calculate and adjust the speed of the aircraft in an attempt to arrive at a point within a defined time limit. This function is not yet well defined for either equipment requirements or airspace implementation. Currently, no Honeywell FMS can claim TOAC capability. This is referenced in Service Information Letter (SIL) D201707000018, which states Honeywell Flight Management System (FMS) PBN capabilities in accordance with AC 90-105A.

For a detailed listing of Honeywell avionics platforms by aircraft type that currently meet or do not meet the requirements for A-RNP under AC 90-105A and ICAO PBN Manual 9613, please reference SIL D201707000018 on the Pilot Gateway.

In summary, A-RNP applications allow qualified aircraft to take full advantage of their navigation and performance capabilities. This will allow the development of more efficient and safer terminal procedures and a higher capacity en route structure.

PBN consists of two kinds of navigation specifications: RNAV and RNP. The important difference between the two is that the RNP specification requires on-board performance monitoring and alerting as part of the avionics functionality. The use of RNP systems offer significant safety, operational, and efficiency benefits. While RNAV and RNP applications will co-exist for several years, it is expected that there will be a gradual transition to RNP applications as the proportion of aircraft equipped with RNP systems increases and the cost to transition is reduced.

FAA has published changes to the AIM effective 28 February 2019. You can download the PDF that lists the changes and includes all of the updated text. The updates of most interest to general aviation pilots focus on the following sections.

The specific capabilities of the GNSS (GPS) in your panel are described in the AFM Supplement and operating handbooks for the equipment (as updated when new system software is installed). You can find more information about RNAV and RNP specs in AC 90-105 and at RNP Procedures and Typical Part 91 Pilots here at BruceAir.

(5) RNP 1. RNP 1 requires a lateral accuracy value of 1 for arrival and departure in the terminal area, and the initial and intermediate approach phase when used on conventional procedures with PBN segments (for example, an ILS with a PBN feeder, IAF, or missed approach). RF turn capability is optional in RNP 1 eligibility. This means that your aircraft may be eligible for RNP 1 operations, but you may not fly an RF turn unless RF turns are also specifically listed as a feature of your avionics suite.

Required Navigation Performance (RNP) is a family of navigation specifications under Performance Based Navigation (PBN) which permit the operation of aircraft along a precise flight path with a high level of accuracy and the ability to determine aircraft position with both accuracy and integrity. RNP offers safety benefits by means of its precision and accuracy and it reduces the cost of operational inefficiencies such as multiple step-down non-precision and circling approaches.

Under the PBN concept, in addition to the RNP navigation specifications there exists the area navigation (RNA) family of navigation specifications. RNAV and RNP navigation specifications are substantially very similar; they only differ in relation to the performance monitoring and alerting requirement which applies to RNP navigation specifications. This means that if the RNP system does not perform the way it should then an alert should be provided to the flight crew. In practical terms what this means is that air traffic control (ATC) can have greater confidence in the track keeping performance of the aircraft and this greater confidence translates into being able to place routes closer together.

RNP refers to the level of performance required for a specific procedure or a specific airspace block. An RNP of 0.3 means the aircraft navigation system must be able to calculate its position to within a circle with a radius of 3 tenths of a NM. The aircraft is required to have both aircraft and operational approval for RNP and the operator must know the level of monitoring provided. FMS equipment with GPS multi-sensor capability meeting TSO-C146 (SBAS/WAAS GPS) meets basic RNP requirements, when installed in an RNP-compliant aircraft installation. The FMS is a key component of an RNP compliant installation. The aircraft operator has to ensure that the aircraft meets the requirements for the specific approval being sought. An operational approval issued by one certification agency will typically be accepted by all, but the operator should ensure that the aircraft meets the requirements for the specific approval being sought or risk denial of access or violation.

RNP 4 is for oceanic and remote continental navigation applications. RNP 2 is for en-route oceanic remote and en-route continental navigation applications. RNP 1 is for arrival and initial, intermediate and missed approach as well as departure navigation applications. Advanced RNP is for navigation in all phases of flight. RNP APCH and RNP AR (authorisation required) APCH are for navigation applications during the approach phase of flight. RNP 0.3 is for the en-route continental, the arrival, the departure and the approach (excluding final approach) phases of flight and is specific to helicopter operations.

The on-board performance monitoring and alerting requirements for RNP 4, RNP 2, Advanced RNP, RNP 1 RNP APCH and RNP 0.3 have common terminology and application. Each of these RNP specifications includes requirements for the following characteristics:

.1,.2,.3 RNP are commonly what you will see out there with more on the way as PBN (performance based navigation) becomes the way. LPV approaches have pretty similar minimums at most airports, just no RF legs.

They are pretty neat to fly in the terrain rich environments. We still have a few tailor made approaches into CYXX and CYLW specific to the 737NG/MAX that we developed. Thing of beauty whatching that terrain display as it goes LNAV/VNAV path all way to mins.