Appendix H H-1 APPENDIX H. ADVANCED REQUIRED NAVIGATION PERFORMANCE (A-RNP) H.1 Introduction.
H.1.1 Performance and Functional Requirements. This appendix provides guidance on the performance and functional requirements for the U.S. A-RNP operational implementation and related operations of:
• Required Navigation Performance (RNP) 2 (domestic or offshore en route),
• RNP 1 instrument departure procedures (DP),
• RNP 1 (RNP Obstacle Departure Procedures (ODP), and Standard Instrument Departures (SID)), and
• RNP 1 Standard Terminal Arrival Routes (STAR).
H.1.2 A-RNP Operations. A-RNP also applies to RNP approaches within the U.S. National Airspace System (NAS) where domestic air traffic control (ATC) procedures are applied.
Additionally, this appendix provides guidance for oceanic and remote continental Areas of Operation where RNP 2, RNP 4, or RNP 10 routes may apply.
Note: This appendix does not address all requirements that may be specified for particular operations. These requirements are specified in other documents, such as national operating rules, Aeronautical Information Publications (AIP), and the International Civil Aviation Organization (ICAO) Doc 7030, Regional Supplementary Procedures (SUPPS). Operators and pilots must adhere to the operational requirements of the appropriate state or regional authority before conducting flights outside of the U.S. NAS.
H.2 Applicable Operators. This appendix applies to all operators conducting A-RNP operations under Title 14 of the Code of Federal Regulations (14 CFR) parts 91, 91 subpart K (part 91K), 121, 125, 129, and 135 within the U.S. NAS or offshore airspace areas.
H.3 Application of A-RNP.
H.3.1 Navigation System Requirements. Navigation systems must have foundational RNP capability (Required Navigation Performance Approach (RNP APCH) to lateral navigation (LNAV), RNP 1, and RNP 2) as a prerequisite to implementing any A-RNP functions.
H.3.2 RNP Functions. Table H-1, RNP Functions, below lists RNP functions beginning with those that are required for the A-RNP qualification in the United States (Scalability, Radius to Fix (RF), and parallel offset). Fix radius transition (FRT) and Time of Arrival Control (TOAC) are optional capabilities that may be included in bundling authorizations discussed in Chapter 12, Bundling Concept, of this advisory circular (AC). Scalability is uniquely an A-RNP function and therefore described in detail in this appendix. The remaining RNP functions are described in Appendix I, Additional Capabilities. It is
Appendix H H-2 necessary to distinguish scalability from the other RNP functions because RF and parallel offset are not uniquely A-RNP functions and are used with other authorizations.
Those operators already qualified to perform RF and/or parallel offset are not required to be A-RNP qualified.
H.3.3 Requirement for A-RNP in the United States. The requirement for A-RNP in the United States is to be operationally and functionally capable of performing scalability, RF, and parallel offset.
H.3.4 Qualification. A-RNP qualification per AC 20-138( ), Airworthiness Approval of Positioning and Navigation Systems, means the aircraft navigation system performs all six A-RNP functions (RF legs, parallel offsets, Area Navigation (RNAV) holding, Scalable RNP, FRTs, and TOAC).
Note: Other States may choose to implement a different subset of functions, or all six functions for their advanced RNP definition.
Table H-1. RNP Functions RNP Function Reference Application Required/Optional Scalability H.5 Appendix A, See Table 5-1 Required for U.S.
Radius to Fix (RF)* I.2 Appendices: A, C, D Required for U.S.
Parallel Offset* I.3 Appendices: E, F Required for U.S.
Fixed Radius Transition (FRT) I.5 Currently not used in U.S. Optional Time of Arrival Control (TOAC) I.6 Currently not used in U.S. Optional Note 1: In addition to RNP functions, higher continuity may be required where specified.
Note 2: *Required for A-RNP in the United States.
H.3.5 Scalable Lateral Navigation. The requirement for scalable lateral navigation accuracy invoked in this AC (optional in the ICAO navigation specification (Nav Spec)) leverages existing aircraft equipage. This functionality, coupled with mandatory RF capability, supports the design of beneficial procedures, especially at locations with high-density traffic or challenging terrain. A-RNP allows for the bundling of approvals across flight phases, improving efficiencies during initial certification and operational use.
H.3.6 Design. A-RNP is designed for operation in oceanic/remote continental airspace, on the domestic or offshore en route structure as well as on arrival, approaches, and DPs.
H.3.7 Multiple Operational Approvals. An A-RNP aircraft qualification may be applied to multiple operational approvals without the need for re-examination of aircraft eligibility.
This enables an operator’s approved procedures, training, etc. to be common to multiple approvals. The A-RNP aircraft qualification will also facilitate multiple operations specifications (OpSpecs).
Appendix H H-3 H.3.8 Features and Requirements. For A-RNP, some features/requirements may be required in one flight phase and optional or unnecessary in another. No distinctions are made regarding flight phase association in providing a general set of criteria spanning all phases and navigation applications. Where such differences are deemed important or the operational need is for one application, a specific operational approval (e.g., RNP 1), is expected to be used instead.
H.3.9 Area Navigation Capability. The area navigation capability required for A-RNP will encompass the lateral aspects of the desired flightpath. The predictability and performance monitoring and alerting for the lateral flightpath will support a number of applications including closely-spaced procedures/routes and operations in terrain-challenged areas.
H.4 Aircraft and System Requirements for A-RNP.
H.4.1 RNP Capability. Navigation systems must have foundational RNP capability (RNP APCH to LNAV, RNP 1, and RNP 2) as a prerequisite to implementing any A-RNP functions.
Note: The system must allow for a means to become established prior to the final approach fix (FAF) on an instrument landing system (ILS) or Ground Based Augmentation System (GBAS) Landing System (GLS) with minimal overshoot or undershoot.
H.4.2 System Requirements. AC 20-138( ) defines the system requirements for A-RNP functions.
H.5 RNP Scalability.
H.5.1 Definition. RNP scalability refers to the ability of the RNP system to automatically retrieve and set the RNP value for each leg segment of a route or procedures from the onboard navigation database. When a change occurs to a smaller RNP value
(e.g., from RNP 1 to RNP 0.3), the change must be completed by the first fix defining the leg with the smaller RNP value requirement. The timing of this change must also consider any latency in alerting from the RNP system.
Note: When the RNP system cannot automatically set the RNP value for each leg segment, operational procedures necessary to manually set the RNP value must be identified.
H.5.2 Usage. Scalable RNP is intended for legs on RNP routes or procedures where ATC, terrain, and/or obstacle considerations provide a benefit on selected legs to using RNP values other than RNP 2 or RNP 1. RTCA/DO-236C, paragraph 3.2.6 provides equipment requirements for assigning an RNP value to a leg and transitions between legs (See Appendix A and Table 5-1).
Appendix H H-4 H.5.3 When Entering into the RNP Navigation System. The RNP scaling, monitoring, and alerting value for scalable legs must be entered into the RNP navigation system automatically from the database. RTCA/DO-236C provides an order of precedence for entering leg RNP values.
Note: Manually entered RNP values for legs are allowed, provided the equipment also changes the scaling, monitoring, and alerting consistent with the RNP value.
H.5.4 Displaying and Entering Values. The RNP system must provide the ability to display and enter RNP values in tenths of a nautical mile (NM) between 0.3 and 2.0.
H.5.5 Small RNP Values. It is acceptable to have a smaller RNP value entered in the RNP navigation system than the leg requires. As an example only to illustrate the point, it is acceptable to have the RNP system set to RNP 1 for a leg that requires RNP 2.
H.5.6 Path Steering Performance. The Original Equipment Manufacturer (OEM) must identify any conditions or constraints on path steering performance (e.g., autopilot (AP)-engaged, flight director (FD) with map display, and/or course deviation indicator (CDI)/map scaling criteria). This is particularly true for RNP values less than RNP 1.
H.5.7 Alerts Prior to an Upcoming Waypoint. The RNP navigation system must provide an alert prior to an upcoming waypoint when the system cannot support the next RNP value.
H.5.8 Deviation Guidance Cues. The deviation guidance cues must be scaled to the RNP value.
H.5.9 Alerts for Failure Modes. The RNP navigation system must provide an alert for any failure mode that potentially affects the navigation performance relative to the selected RNP value. Failure modes may include loss of electrical power, loss of signal reception, and RNP equipment failure, including navigation performance degradation, resulting in a loss of RNP containment integrity. The applicant should verify that a visible alert occurs within the flightcrew’s primary field of view (FOV) when loss of navigation capability and/or loss of integrity are experienced.
H.6 Operational Approval for A-RNP Operations.
H.6.1 Certification and Recognition. Airworthiness certification and recognition of A-RNP aircraft qualification alone does not authorize A-RNP operations. Operational approval is also required to confirm the operator has acceptable normal and contingency procedures for A-RNP operations.
H.6.2 Aircraft Qualification Documents. The aircraft or avionics manufacturers should develop aircraft qualification documentation that shows compliance with the applicable criteria.
H.6.3 Performance Requirements Review. Prior to application, operators and manufacturers of their equipment should review all performance requirements. Installation of equipment by itself does not guarantee operational approval or permit operational use.
Appendix H H-5 H.7 FAA Acceptance of Documentation.
H.7.1 New Aircraft/Equipment. The aircraft/equipment qualification documentation can be approved as part of an aircraft certification project and reflected in the Airplane Flight Manual (AFM) and related documents.
H.7.2 Existing Aircraft/Equipment. For installations/equipment not previously approved to conduct A-RNP procedures, the aircraft or avionics manufacturer should submit the A-RNP documentation in accordance with AC 20-138( ). The operator will submit the RNP operational application package (if required) to the Federal Aviation Administration (FAA).
H.8 Operational Considerations.
H.8.1 RNP Operations within the U.S. NAS. For systems with receiver autonomous integrity monitoring (RAIM)-based integrity, a RAIM prediction must be performed prior to departure. This capability can be a ground service and need not be resident in the aircraft’s avionics equipment. Preflight integrity checks and the various capabilities that can be utilized to perform them can be found in Chapter 9, Flight Planning, of this AC.
H.8.2 RNP Operations in Oceanic and Remote Continental Areas. The operator must have an approved Global Navigation Satellite System (GNSS) availability prediction program ensuring the requisite availability of the GNSS fault detection and exclusion (FDE) function. Prior to conducting RNP operations in oceanic or remote continental areas, the operator must use this prediction program prior to dispatch.
H.8.3 General In-Flight Considerations. At system initialization, pilots must confirm the navigation database is current and verify that the aircraft position has been entered correctly. Pilots must not fly an RNP procedure unless it is retrievable by name from the onboard navigation database and conforms to the chart. An RNP route, RNP SID, RNP STAR, or RNP APCH should not be used if doubt exists as to the validity of the procedure in the navigation database.
Note 1: For flexible route structures, manual entry of waypoints (i.e., latitude and longitude), may be permitted provided the potential for entry error by pilots is mitigated by adequate flightcrew procedures. The manual entry or creation of new waypoints, by manual entry of latitude and longitude or rho/theta values for fixed, published routes is not permitted. The pilot may modify the route through the insertion or deletion of specific waypoints in response to ATC clearances.
Pilots must not change any database waypoint type from a flyby to a flyover or vice versa.
Note 2: Flightcrew may notice a slight difference between the navigation information portrayed on the chart and their primary navigation display.
Differences of 3 degrees or less may result from equipment manufacturer’s application of magnetic variation and are operationally acceptable.
Appendix H H-6 H.8.3.1 The pilot must confirm the correct procedure is selected. This process includes confirmation of the waypoint sequence, reasonableness of track angles and distances, and any other parameters that can be altered by the pilot, such as altitude or speed constraints. A navigation system textual display or navigation map display must be used.
H.8.3.2 Determine cross-track (XTK) error/deviation. More specifically, the maximum deviations allowed to support A-RNP must be understood and respected.
H.8.3.3 It is important to maintain the published path and maximum airspeeds while performing A-RNP operations with RF legs or FRTs.
H.8.3.4 For A-RNP procedures, pilots must use a lateral deviation indicator, FD, or AP in LNAV mode. Pilots of aircraft with a lateral deviation display must ensure lateral deviation scaling is suitable for the RNP value associated with the procedure.
H.8.3.5 The pilot must be able to use RNP equipment to follow flight guidance for LNAV no later than 500 feet above the airport elevation.
H.8.3.6 Some aircraft do not display or compute a path during flyby turns. As such, pilots of these aircraft may not be able to adhere to half the lateral navigation accuracy during turns but are still expected to satisfy the standard during intercepts following turns and on straight segments. This does not apply to the execution of either FRT or RF procedures.
H.8.3.7 Operational qualification for RNP procedures requires flightcrew monitoring of lateral and, if installed, vertical deviations on the pilot’s primary flight displays (PFD) to ensure the aircraft remains within the bounds defined by the procedure. The deviation must be monitored, and action taken to minimize errors during all RNP operations.
H.8.3.8 If ATC issues a heading assignment taking the aircraft off a procedure, the pilot should not modify the primary flight plan in the RNP system until a clearance is received to rejoin the route or the controller confirms a new route clearance. The specified accuracy requirement does not apply when the aircraft is not on the published A-RNP procedure.
H.8.3.9 The flightcrew must be able to assess the impact of equipment failure on the anticipated RNP operation and take appropriate action.
H.8.3.10 Whenever possible, RNP routes should be extracted from the database in their entirety, rather than loading RNP route waypoints from the database into the flight plan individually. Selecting and inserting individual, named fixes from the database is permitted, provided all fixes along the published route to be flown are inserted. Expanded coordinates of named fixes extracted from the database should be verified.
Appendix H H-7 H.8.3.11 Pilots of aircraft with RNP input selection capability should select the smallest RNP value for the route or procedure that ensures the RNP system offers appropriate lateral deviation scaling permitting the pilot to monitor lateral deviation and meet the requirements of the A-RNP operation.
H.8.3.12 If the navigation system does not automatically retrieve and set the RNP value from the onboard navigation database for each leg segment of a route or procedure, the flightcrew’s operating procedures should verify the appropriate RNP value for the route or procedure is manually entered into the RNP system.
H.8.4 Prior to Commencing the A-RNP Procedure. In addition to normal operating procedures, prior to commencing the procedure, the flightcrew should accomplish the following:
1. The flightcrew must confirm that the correct procedure has been selected. This process includes confirmation of the waypoint sequence, reasonableness of track angles, distances, and any other parameters that can be altered by the pilot. A procedure must not be used if validity of the navigation database is in doubt. A navigation system textual display or navigation map display must be used.
2. For multisensor systems, crew must verify that the correct sensor is being used for position computation.
H.8.5 Contingency Procedures. The pilot must notify ATC of any loss of the RNP capability (integrity alerts or loss of navigation), together with the proposed course of action. If unable to comply with the requirements of an RNP procedure, pilots must advise ATC as soon as possible. The loss of RNP capability includes any failure or event causing the aircraft to no longer satisfy the RNP requirements of the route.
H.8.6 Scalability Considerations. The RNP system should automatically retrieve and set the RNP value for each leg segment of a route or procedure from the onboard navigation database. When a change occurs to a smaller RNP value, (e.g., from RNP 1 to RNP 0.3), the change must be complete by the first fix defining the leg with the smaller RNP value requirement. The timing of this change must also consider any latency in alerting from the RNP system. When the RNP system cannot automatically set the RNP value for each leg segment, any operational procedures necessary to accomplish this must be identified.
Note: RNP scalability is an FAA requirement for A-RNP operators.
H.8.6.1 One acceptable means to meet this requirement may be to require the flightcrew to manually set the smallest RNP value the route or procedure uses before commencing the route or procedure (i.e., prior to the initial approach fix (IAF)).
H.8.6.2 If the RNP value for the RNP system has been set manually by the flightcrew and following an RNP system change to the RNP value required (e.g., the next
Appendix H H-8 flightpath segment contains a different RNP value), the RNP system should provide an alert to the flightcrew.
Note: One means by which this can be achieved is as described in RTCA, Inc., DO-283A, Minimum Operational Performance Standards for Required Navigation Performance for Area Navigation. Another means is to develop lateral deviation displays and alerting as per RTCA, Inc./European Organization for Civil Aviation Equipment (EUROCAE) Minimum Aviation System Performance Standard (MASPS) DO-236C/ED-75.
H.8.6.3 The RNP system must provide lateral deviation displays and alerting appropriate to the selected RNP value and application.
H.8.6.4 It is recognized that aircraft and equipment based upon Global Positioning System (GPS) standards such as RTCA DO-208 and DO-229( ) have RNP capabilities for lateral deviation and alerting that are generally associated with navigation accuracies of 0.3, 1.0, and 2.0 NM only. Such capability exists in a large portion of the aircraft fleet, but may not be extended to other navigation accuracies or the means of compliance specified herein. Additionally, some of this fleet does provide the capability to select other navigation accuracies.
Therefore, before a manufacturer implements or an operator applies this functional capability, it is recommended that they determine the effects of the resolution of a number of issues including:
1. How their aircraft and systems will be affected or accommodated operationally when different navigation accuracy requirements are needed,
2. Is there a basis for implementing improved functionality or operating procedures, and
3. How such systems will need to be qualified, used by the flightcrew and operationally approved.
H.9 A-RNP Aircrew Training. A-RNP training should include the following:
1. Demonstrate continuity of RNP systems as part of contingency procedures,
2. Retrieve and fly a RF procedure,
3. Retrieve and fly a parallel offset, and
4. Demonstrate RNP scalability (The RNP system must be capable of manual or automatic entry and display of RNP value requirements).
Appendix I I-1 APPENDIX I. ADDITIONAL CAPABILITIES I.1 Introduction.
I.1.1 Guidance. This appendix provides guidance on the performance, functional and additional operational requirements for Required Navigation Performance (RNP) systems containing additional capabilities.
I.1.2 Applicability. This appendix applies to all operators conducting RNP operations under Title 14 of the Code of Federal Regulations (14 CFR) parts 91, 91 subpart K (part 91K), 121, 125, 129, and 135 within the U.S. National Airspace System (NAS) or offshore airspace areas.
I.2 Radius to Fix (RF).
I.2.1 Description of RF Legs.
I.2.1.1 RF legs are an optional capability for use with:
• Required Navigation Performance Approach (RNP APCH) (Appendix A, Qualification Criteria for Required Navigation Performance Approach (RNP APCH) Operations;
• RNP 1 (Appendix C, Qualification Criteria for Required Navigation Performance (RNP) 1 (Terminal) Operations); and
• RNP 0.3 (Appendix D, Qualification Criteria for Required Navigation Performance (RNP) 0.3 (Rotorcraft) Operations).
I.2.1.2 This functionality can be used in the following:
• Initial and intermediate approach segments;
• Final phase of the missed approach;
• Standard Instrument Departures (SID); and
• Standard Terminal Arrival Routes (STAR).
I.2.1.3 The application of RF legs in the final approach, initial or intermediate phases of the missed approach is prohibited. Such procedure segments wishing to apply RF would have to use the Required Navigation Performance Authorization Required (RNP AR) specification (Refer to Advisory Circular (AC) 20-138( ), Airworthiness Approval of Positioning and Navigation Systems, and AC 90-101( ), Approval Guidance for RNP Procedures with AR).
I.2.2 Path Definition. The RNP lateral accuracy requirement is evaluated around the path defined by the published procedure and RTCA, Inc.’s document, RTCA/DO-236( ).
Appendix I I-2 Note: Industry standards for paths can be found in RTCA/DO-236C( ).
I.2.3 Demonstration of Path Steering Performance. The navigation system must have the capability to execute leg transitions and maintain tracks consistent with an RF leg between two fixes. There is no requirement for the aircraft to include a redundant navigation capability to perform RF legs should a loss of navigation occur during the RF leg. However, type certificate (TC) or Supplemental Type Certificate (STC) applicants for RNP approval that include RF legs are encouraged to provide a redundant navigation capability on the aircraft that can maintain the RF leg track.
I.2.3.1 The Airplane Flight Manual (AFM)/Rotorcraft Flight Manual (RFM) or aircraft qualification guidance should document limitations if:
1. The aircraft cannot proceed “Direct-To” the initial fix defining an RF leg segment.
2. The aircraft cannot accept a radar vector (a heading assigned by air traffic control (ATC)) to the middle of an RF leg segment for intercepting and completing the RF leg segment from that point while sustaining the desired level of performance.
I.2.4 Flight Technical Error (FTE). System documentation should support maintenance of FTE (95 percent of the flying time) during straight and curved path segments, for each phase of flight and each autopilot (AP) and/or flight director (FD) mode requested. If documenting FTE values other than those listed in RTCA/DO-283A, the documentation must show demonstration in accordance with AC 120-29( ), Criteria for Approval of Category I and Category II Weather Minima for Approach, or AC 20-138( ).
I.2.5 Interface to Flight Guidance System (FGS). An acceptable AP and/or FD response to an RNP system failure or loss must be verified in each AP and FD mode, as applicable.
Note: If AP malfunction testing was performed for worst case failures, no further validation is required. In this case, the manufacturer must provide a statement of confirmation.
I.2.6 Failure Modes/Annunciation. System documentation should identify any failure modes potentially affecting RNP system RF leg capability. Failure modes may include loss of electrical power, loss of signal reception, and RNP equipment failure including degradation of navigation performance resulting in a loss of RNP containment integrity.
The applicant should verify that a visible alert occurs within the flightcrew’s primary field of view (FOV) when loss of navigation capability and/or loss of integrity are experienced.
I.2.7 Functional Requirements. RNP procedures with RF legs require the use of an AP or FD with at least “roll-steering” capability that is driven by the RNP system. The AP/FD must operate with suitable accuracy to track the lateral and, as appropriate vertical paths required by a specific RNP procedure.
Appendix I I-3 I.2.7.1 The aircraft must have an electronic map display depicting the RNP-computed path of the selected procedure.
I.2.7.2 The flight management computer (FMC), the FD system, and the AP must be capable of commanding a bank angle up to 30 degrees above 400 feet above ground level (AGL).
I.2.7.3 The specified bank angles comply with RTCA/DO-236C and are consistent with a common procedure design criteria that accommodates all aircraft categories; including those with the highest approach speeds. Aircraft with lower approach speeds will typically not achieve these bank angles in normal operations.
I.2.8 Maintaining Lateral Navigation (LNAV) in Missed Approach. If abandoning a procedure while on an RF leg or initiating a go-around or missed approach (through activation of takeoff/go-around (TOGA) or other means), the flight guidance mode should remain in LNAV to enable display of deviation and positive course guidance during an RF leg, including the missed approach segment. If the aircraft does not provide this capability, crew procedures must be used that assure the aircraft will adhere to the specified flightpath during the RF leg segment.
Note: For missed approaches with a RF leg, the flightcrew must be able to couple the AP or FD to the RNP system (engage LNAV) by 500 feet AGL.
I.2.9 Crew Workload Analysis. Analyze the crew workload and determine acceptability when flying and monitoring track adherence in association with RF legs during all phases of flight, including those non-normal procedures that can be evaluated in-flight.
I.2.10 Eligibility Airworthiness Documents. The flight manual or referenced document should contain the following information:
1. A statement indicating the aircraft meets the requirements for RNP operations with RF legs and has demonstrated the established minimum capabilities for these operations. This documentation should include the phase of flight, mode of flight (e.g., FD on or off; and/or AP on or off, and applicable lateral and vertical modes), minimum demonstrated RNP value, and sensor limitations, if any.
2. Any conditions or constraints on path steering performance (e.g., AP-engaged, FD with map display, including lateral and vertical modes, and/or course deviation indicator (CDI)/map scaling requirements) should be identified.
Use of manual control with CDI only is not allowed on RF legs.
3. The criteria used for the demonstration of the system includes:
• Acceptable normal and non-normal procedures,
• Demonstrated configurations,
Appendix I I-4
• Type of facilities used, and
• Any constraints or limitations necessary for safe operation should be identified.
I.3 Parallel Offset.
I.3.1 Description of Parallel Offset. Parallel offsets provide a capability to fly offset from the parent track, as defined by the series of waypoints. Parallel offset capability is required for an A-RNP qualification and mandatory for oceanic/remote continental RNP 2 (Appendix E) and RNP 4 (Appendix F) operations. The turn defined for the parent track (flyby or fixed radius transitions (FRT)) must be applied in the offset track. Parallel offsets are applicable only for en route segments and are not foreseen to be applied on SIDs, STARs, or approach procedures. The activation of an offset must be clearly displayed to the flightcrew with the cross-track (XTK) deviation indication to the offset track.
I.3.2 Usage of Parallel Offset. Parallel offsets can be used on route segments in en route and terminal areas, and are intended to replicate all of the centerline route characteristics at the desired offset to the left or right of the centerline route. Parallel offsets are not intended for approach segments, arrivals, or departures. RTCA/DO-236C, paragraphs 3.2.4.3 and 3.7.2.2.4 provide detailed requirements for implementing parallel offsets in RNP equipment.
I.3.3 Parallel Offset Considerations. The system should be capable of flying tracks offset by up to 20 nautical miles (NM) from the parent track. The presence of an offset should be continuously indicated. Tracks offset from the parent track must be continued for all Air Traffic Service (ATS) route segments and turns until either removed by the crew or automatically cancelled by:
1. Amendment of the active flight plan by executing a “Direct-To,”
2. Commencement of an approach procedure, or
3. Where a course change exceeds 90 degrees. The navigation system can be expected to terminate the offset no later than the fix where the course change occurs. The offset may also be terminated if the route segment ends at a hold fix.
I.3.4 Lateral Offset Activation. When a lateral offset is activated in the Area Navigation (RNAV) or RNP system, the aircraft will leave the defined route and typically intercept the offset at an angle of 45 degrees or less. When the offset is cancelled, the aircraft returns to the defined route in a similar manner.
I.4 RNAV Holding.
I.4.1 Usage of RNAV Holding. RNAV holding is intended to give aircraft the ability to fly either ATC-defined ad hoc or published holding patterns with the performance, monitoring, and alerting abilities associated with RNP. RTCA/DO-236C,