Appendix E E-4 operator can revert to a different navigation system and proceed to a suitable airport.
Note: Operators and pilots are required to use the specified continuity requirements of the governing state or regional authority before conducting flights outside of the U.S. NAS.
E.4.2.2 Performance Monitoring and Alerting. The RNP system, or the RNP system and pilot in combination, must provide an alert if the accuracy requirement is not met, or if the probability that the lateral TSE exceeds 4 NM is greater than 10-5 for RNP 2 operations.
E.4.2.3 Path Definition. Aircraft performance is evaluated around the path defined by the published procedure and RTCA/DO-236C.
E.4.2.4 Signal in Space (SIS). The aircraft navigation equipment must provide an alert if the probability of SIS errors causing a lateral position error greater than 4 NM exceeds 10-7 per hour for RNP 2 operations.
E.5 Maintenance Requirements.
E.5.1 LRNS. Aircraft must have established maintenance procedures for all LRNS intended for use in oceanic and remote continental area operations.
E.6 Functional Requirements of Navigation Data Displays.
E.6.1 Installation. The following navigation displays and functions are required and must be installed in accordance with AC 20-138( ) or equivalent airworthiness installation advisory material.
E.6.2 Navigation Data Displays. Navigation data, including a TO/FROM indication and a failure indicator, must be displayed on a lateral deviation display (course deviation indicator (CDI), electronic horizontal-situation indicator (EHSI)) and/or a navigation map display. These must be used as primary flight instruments for the navigation of the aircraft, for maneuver anticipation and for failure/status/integrity indication. A non-numeric lateral deviation display (e.g., CDI, EHSI), with a TO/FROM indication and a failure annunciation, for use as primary flight instruments for navigation of the aircraft, for maneuver anticipation, and for failure/status/integrity indication, should have the following attributes:
1. The displays must be visible to the pilot and located in the primary field of view (FOV).
2. The lateral deviation display scaling must agree with any alerting and annunciation limits.
3. The lateral deviation display must have a full-scale deflection suitable for the current phase of flight and must be based on the required total system
Appendix E E-5 accuracy; ±2 NM for RNP 2. It is also acceptable for the scaling to be more conservative (e.g., ±1 NM for an RNP 2 route).
4. The display scaling may be set automatically by default logic or to a value obtained from a navigation database. The full-scale deflection value must be known or must be available for display to the pilot commensurate with the required track-keeping accuracy.
5. The lateral deviation display must be automatically slaved to the RNP-computed path. It is recommended that the course selector of the deviation display be automatically slewed to the RNP-computed path.
Note: This does not apply for installations where an electronic map display contains a graphical display of the flightpath and path deviation.
6. As an alternate means, a navigation map display must give equivalent functionality to a lateral deviation display with appropriate map scales (scaling may be set manually by the pilot). To be approved as an alternative means, the navigation map display must be shown to meet the TSE requirements and be located in the primary FOV.
7. It is not necessary for navigation displays, particularly primary flight displays (PFD), to include an Actual Navigation Performance (ANP) or RNP value.
The displays only need to provide an alert if the RNP for the operation cannot be met.
E.6.3 System Capabilities. The following system capabilities are required as a minimum within any RNP 2 equipment:
1. The capability to continuously display to the pilot flying (PF), on the primary flight instruments for navigation of the aircraft (primary navigation display), the RNP-computed desired path and aircraft position relative to the path. For operations where the required minimum flightcrew is two pilots, a means for the pilot monitoring (PM) to verify the desired path and the aircraft position relative to the path must also be provided.
2. A navigation database, containing current navigation data officially promulgated for civil aviation, which can be updated in accordance with the Aeronautical Information Regulation and Control (AIRAC). The stored resolution of the data must be sufficient to achieve the required track-keeping accuracy. The database must be protected against pilot modification of the stored data.
3. The means to display the validity period of the navigation data to the pilot.
4. The means to retrieve and display data stored in the navigation database relating to individual waypoints and navigation aids, to enable the pilot to verify the route to be flown.
5. The capability to load from the database into the RNP system the RNP 2 route to be flown if applicable.
Appendix E E-6 Note 1: It is acceptable to manually load en route and terminal waypoints from the database into a flight plan page and manually set the scaling and alerting.
Note 2: Due to variability in systems, this document defines the segment from the first occurrence of a named waypoint, track, or course to the last occurrence of a named waypoint, track, or course. Heading legs prior to the first named waypoint or after the last named waypoint do not have to be loaded from the database.
6. The capability to automatically set RNP 2 from the onboard navigation database for each leg segment of a RNP 2 route or procedure.
7. For RNP 2 tracks in oceanic/remote continental airspace using flexible
(e.g., organized) tracks, a means to enter the unique waypoints required to build a track assigned by the ATS provider. Manual entry or creation of new waypoints is permitted, by manual entry of latitude and longitude.
8. The means to display the following items, either in the pilot’s primary FOV, or on a readily accessible display page:
• The active navigation sensor type,
• The identification of the active (To) waypoint,
• The ground speed and time to the active (To) waypoint, and
• The distance and bearing to the active (To) waypoint.
9. The capability to execute a “direct to” function.
10. The capability to execute a parallel offset (Appendix I, Additional Capabilities).
Note: The system must have the capability to fly parallel tracks at a selected offset distance. When executing a parallel offset (Appendix I), the RNP type and all performance requirements of the original route in the active flight plan must be applicable to the offset route. The system must provide for entry of offset distances in increments of 1 NM, left or right of course. The system must be capable of offsets of at least 20 NM.
11. The capability for automatic leg sequencing with display to the pilots.
12. The capability to automatically execute waypoint transitions and maintain track consistent with the RNP 2 performance requirements with the following Aeronautical Radio, Inc. (ARINC) Specification 424 path terminators:
• Course to Fix (CF),
• Direct to Fix (DF), and
• Track to Fix (TF).
Appendix E E-7 Note: Path terminators are defined in ARINC Specification 424, and their application is described in more detail in RTCA documents, DO-236( ) and DO-201( ).
13. The capability to display an indication of the RNP 2 system failure in the pilot’s primary FOV.
14. The capability to indicate to the crew when the Navigation System Error (NSE) alert limit is exceeded (i.e., the alert provided by the onboard performance monitoring and alerting function).
15. Capability for the crew to create, review and activate a flight plan.
Note: The system must provide the capability for modification (e.g., deletion and addition of fixes and creation of ATRK fixes), review and user acceptance of changes to the flight plans. When this capability is exercised, guidance outputs must not be affected until modification(s) is/are activated. Activation of any flight plan modification must require positive action by the flightcrew after input and verification by the flightcrew.
16. The system must provide data to enable the generation of command signals for AP/FD/CDI, as applicable. In all cases, a FTE must be defined at the time of certification, which will meet the requirements of the desired RNP operation in combination with the other system errors.
E.6.4 Database Integrity. The operator must ensure their navigation database supplier possesses a Type 2 Letter of Acceptance (LOA) in accordance with AC 20-153( ), Acceptance of Aeronautical Data Processes and Associated Databases.
E.6.5 Path Terminators. The database supplier should not substitute path terminators in lieu of those specified in the original State AIP data.
E.7 Aircraft Eligibility.
E.7.1 System Eligibility for RNP 2 Operations. Systems meeting the requirements in AC 20-138( ) are eligible for RNP 2 operations.
E.8 Operational Requirements.
E.8.1 Navigation Equipage. To satisfy the higher continuity requirement, all RNP 2 operations in oceanic and remote continental areas must have at least dual independent GPS LRNS.
E.8.2 Configuration. The equipment configuration used to demonstrate the required accuracy must be identical to the configuration, which is specified in the minimum equipment list (MEL).
E.8.2.1 The operator must have an approved GNSS availability prediction program ensuring the requisite availability of the GNSS FDE function. Prior to conducting RNP 2 operations oceanic or remote continental areas, the
Appendix E E-8 operator must use this prediction program prior to dispatch. In the event of a predicted, continuous loss of appropriate level of fault detection of more than 5 minutes for any part of the RNP 2 operation, the operator should revise the flight plan (e.g., delay the departure or plan a different route).
E.8.3 Aircraft Qualification Documentation. The aircraft or avionics manufacturers should develop aircraft qualification documentation that shows compliance with the applicable criteria, as appropriate. This is not required for aircraft with an AFM or AFMS which explicitly states that the RNP system is approved for instrument flight rules (IFR) operations with RNP values at least as low as RNP 2 and the equipment meets the performance and reliability guidance of AC 20-138( ).
E.8.3.1 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.
E.9 Operational Considerations.
E.9.1 Pilot Training and Qualification. Operators should ensure pilots are trained and qualified to operate in RNP 2 airspace.
E.9.2 Preflight Planning. The following actions should be completed during preflight:
1. Review maintenance logs and forms to ascertain the condition of equipment required for flight in RNP 2 airspace or on an RNP 2 route, and
2. Ensure that maintenance action has been taken to correct defects to required equipment.
E.9.3 Domestic Operations. For systems with RAIM-based integrity, 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.
E.9.4 Oceanic and Remote Continental Operations. RAIM availability prediction should take into account the latest GNSS constellation, Notices to Airmen (NOTAM), and avionics model (when available). The ANSP, avionics manufacturer, or the RNP system may provide this service.
E.9.4.1 In the event of a predicted, continuous loss of an appropriate level of FDE of more than 5 minutes for any part of the RNP 2 operation, the operator should revise the flight plan (e.g., delay the departure or plan a different route).
E.9.4.2 RAIM availability prediction software does not guarantee the service; rather, RAIM prediction tools assess the expected capability to meet the RNP.
Because of unplanned failure of some GNSS elements, pilots and ANSPs must realize that RAIM or GNSS navigation may be lost while airborne, and
Appendix E E-9 this may require reversion to an alternative means of navigation. Therefore, pilots should prepare to assess their capability to navigate (potentially to an alternate destination) in case of failure of GNSS navigation.
E.9.5 General In-Flight Considerations. 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.
E.9.5.1 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.
Note: 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.
E.9.5.2 For RNP 2 operations, pilots must use a lateral deviation indicator, FD, or AP in lateral navigation (LNAV) mode. Pilots of aircraft with a lateral deviation display must ensure lateral deviation scaling is suitable for the RNP 2 operation.
E.9.5.3 At least two independent LRNS capable of navigating to the RNP should be operational at the oceanic entry point. If this is not the case, the pilot should consider an alternate routing or divert for repairs.
E.9.5.4 If the navigation system does not automatically retrieve and set RNP 2 from the onboard navigation database for the entirety of the RNP 2 operation, the flightcrew’s operating procedures must manually set RNP 2. This ensures proper RNP system monitoring and alerting is available for the RNP 2 operation.
E.9.5.5 Operator in-flight procedures must include verifying the RNP value set in the FMS matches the equipment capability and authorizations as annotated in the flight plan prior to entering oceanic and remote continental airspace.
E.9.5.6 Operator in-flight operating procedures must include mandatory cross-checking procedures to identify navigation errors in sufficient time to prevent aircraft from an inadvertent deviation from ATC-cleared routes.
Appendix E E-10 E.9.5.7 Crews must advise ATC of any deterioration or failure of the navigation equipment below the navigation performance requirements or of any deviations required for a contingency procedure.
E.9.5.8 All pilots are expected to maintain centerline, as depicted by onboard lateral deviation indicators and/or flight guidance during all RNP operations described in this AC unless authorized to deviate by ATC, performing a Strategic Lateral Offset Procedure (SLOP), or under emergency conditions.
For normal operations, cross-track (XTK) error/deviation (the difference between the displayed path and the displayed aircraft position relative to the displayed path, (i.e., FTE)) should be limited to half the RNP value associated with the procedure (i.e., 1 NM for RNP 2). Brief deviations from this standard
(e.g., overshoots or undershoots) during and immediately after turns, up to a maximum of one times the RNP value (i.e., 2 NM for RNP 2), are allowable.
Note: 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 fixed radius transition (FRT) or Radius to Fix (RF) procedures.
E.9.5.9 Operational qualification for RNP procedures requires flightcrew monitoring of lateral and, if installed, vertical deviations on the pilot’s PFDs 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.
E.9.5.10 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 RNP 2 procedure.
E.9.5.11 The flightcrew must be able to assess the impact of equipment failure on the anticipated RNP operation and take appropriate action.
E.9.5.12 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.
E.9.5.13 Pilots of aircraft with RNP input selection capability should select an RNP value of 2 NM, or smaller. The selection of the RNP value should ensure the RNP system offers appropriate lateral deviation scaling permitting the pilot to monitor lateral deviation and meet the requirements of the RNP 2 operation.
Appendix E E-11 E.9.5.14 Emergency procedures for operations in RNP 2 airspace or on RNP 2 routes are no different than normal oceanic emergency procedures with one exception, crews must be able to recognize and ATC must be advised when the aircraft is no longer able to navigate to its RNP 2 approved capability.
E.9.6 Prior to Commencing the RNP 2 Procedure. In addition to normal operating procedures, prior to commencing the procedure the flightcrew should accomplish the following:
1. For multisensor systems, crew must verify that the correct sensor is being used for position computation; and
2. Where Controller-Pilot Data Link Communication (CPDLC) is used to uplink flight plan changes for routing that is not contained in the navigation database, the flightcrew should confirm the RNP in effect matches the airspace requirement. If not, the flightcrew should manually enter the RNP applicable to the route.
Appendix F F-1 APPENDIX F. QUALIFICATION CRITERIA FOR REQUIRED NAVIGATION PERFORMANCE (RNP) 4 OCEANIC AND REMOTE CONTINENTAL OPERATIONS F.1 Introduction.
F.1.1 Performance and Functional Requirements. This appendix provides guidance on the performance and functional requirements for systems used to conduct RNP 4 over oceanic and remote continental airspace. Previous authorizations in accordance with FAA Order 8400.33, Procedures for Obtaining Authorization for Required Navigation Performance 4 (RNP-4) Oceanic and Remote Area Operations, remain valid. This appendix does not address communications or surveillance requirements that may be specified to operate on a particular route or in a particular area. Those requirements are specified in other documents, such as the Aeronautical Information Publications (AIP) and the International Civil Aviation Organization (ICAO) Doc 7030, Regional Supplementary Procedures (SUPPS) and ICAO Doc 4444 PANS ATM, Procedures for Air Navigation Services, Air Traffic Management.
F.2 Aircraft and System Requirements for RNP 4.
F.2.1 Statement of Compliance (SOC). Aircraft with an SOC with RNP 4 criteria in Advisory Circular (AC) 20-138( ), Airworthiness Approval of Positioning and Navigation Systems, in their Airplane Flight Manual (AFM), Airplane Flight Manual Supplement (AFMS), pilot’s operating handbook (POH), or the operating manual for their avionics meet the performance and functional requirements of this appendix.
F.2.2 Statement from the Manufacturer. Aircraft with a statement from the manufacturer documenting compliance with the RNP 4 criteria in AC 20-138( ) meet the performance and functional requirements of this AC. These statements should include the airworthiness basis for compliance. Compliance with the sensor requirements will have to be determined by the equipment or aircraft manufacturer, while compliance with the functional requirements in this appendix may be determined by the manufacturer or by inspection by the operator.
F.2.3 Navigation Equipment Requirements. Navigation equipage for all RNP 4 operations in oceanic and remote continental areas must have at least dual independent long-range navigation systems (LRNS). Global Navigation Satellite System (GNSS) must be used as either a stand-alone navigation system, as one of the sensors in a multisensor system, or as part of an integrated GNSS/inertial system.
Note: RNP 4 operations are based on Global Positioning System (GPS) positioning. Positioning data from other types of navigation sensors may be integrated with the GPS data provided it does not cause position errors exceeding the Total System Error (TSE) budget. Otherwise, means should be provided to deselect the other navigation sensor types.
Appendix F F-2 F.3 System Performance, Monitoring, and Alerting.
F.3.1 Accuracy. The aircraft must comply with Section 2.1.1 of RTCA/DO-236( ). During operations in airspace or on routes designated as RNP 4, the lateral TSE must be within ±4 nautical miles (NM) for at least 95 percent of the total flight time. The along-track (ATRK) error must also be within ±4 NM for at least 95 percent of the total flight time.
To satisfy the 95 percent accuracy requirement, the Flight Technical Error (FTE) should not exceed 2 NM.
Note: The use of a lateral deviation indicator with 4 NM full-scale deflection has been found to be an acceptable means of compliance (AMC) integrity.
F.3.2 Integrity. Malfunction of the aircraft navigation equipment that causes the TSE to exceed two times the RNP value is classified as a major failure condition under airworthiness guidance (i.e., 10-5 per hour).
F.3.3 Continuity. For RNP 4, loss of navigation equipment function is a major failure condition. The continuity requirement is satisfied by the carriage of dual independent LRNSs (excluding Signal in Space (SIS)).
Note: Operators and pilots are required to use the specified continuity requirements of the governing state or regional authority before conducting flights outside of the U.S. National Airspace System (NAS).
F.3.4 Performance Monitoring and Alerting. The RNP system, or the RNP system and pilot in combination, must provide an alert if the accuracy requirement is not met, or if the probability that the lateral TSE exceeds 2 x RNP (8 NM) is greater than 10-5 for RNP 4 operations.
F.3.4.1 Onboard performance monitoring and alerting compliance does not imply an automatic monitor of FTE. The onboard monitoring and alerting function should at least consist of a Navigation System Error (NSE) monitoring and alerting algorithm and a lateral deviation display enabling the crew to monitor the FTE.
F.3.4.2 Path Definition Error (PDE) is considered negligible.
F.3.5 SIS. If using GPS, the aircraft navigation equipment must provide an alert if the probability of SIS errors causing a lateral position error greater than 8 NM exceeds 10-7 per hour for RNP 4 operations.
Note: For RNP systems where the architecture is an integrated, multisensor capability and where GNSS integrity is incorporated into a 2 x RNP integrity alert consistent with DO-236( ) where performance cannot be met, a separate GNSS integrity alert is not required.
Appendix F F-3 F.4 Aircraft Eligibility.
F.4.1 Detection Methods. There are two methods to recognize aircraft and system eligibility for RNP 4 operations: 1) RNP certification; and, 2) prior navigation system certification. In both cases, the aircraft must be equipped with at least two independent and serviceable LRNSs; at least one of which must be GNSS.
F.4.2 RNP Certification. RNP certification is typically documented in the AFM/AFMS for aircraft that have been formally certificated and approved for RNP operations and typically is not limited to RNP 4. The AFM/AFMS addresses RNP levels that have been demonstrated to meet the certification criteria and any related provisions applicable to their use (e.g., navigation aid sensor requirements). Operational approval is based upon the performance stated in the AFM/AFMS and pilot qualification. This method also applies in cases where certification is received through a Supplemental Type Certificate (STC) issued to retrofit equipment, such as GNSS receivers, to enable the aircraft to meet RNP 4 performance criteria in oceanic and remote continental area airspace.
F.4.2.1 This method is used to approve aircraft whose level of performance under previous standards equates to the RNP 4 criteria listed in this AC. The AFM/AFMS must indicate the aircraft is equipped with GNSS approved as a LRNS for oceanic and remote continental airspace operations.
F.4.2.2 RNP 4 operations using only GNSS is based upon a predeparture fault detection and exclusion (FDE) availability prediction program. Twenty-five minutes is the maximum allowable time for which FDE capability is projected to be unavailable on any one event. This maximum outage time must be included as a condition of the RNP 4 operational approval. If predictions indicate that the maximum allowable FDE outage will be exceeded, the operation must be rescheduled to a time when FDE is available.
1. Aircraft with Technical Standard Order (TSO)-C129( ) equipment must also document the equipment is approved for oceanic operations according to AC 20-138( ), Appendix 1.
2. TSO-C115b (or later revision) is acceptable for multisensor systems incorporating GNSS sensors.
F.4.2.3 Multisensor systems incorporating an approved inertial navigation system (INS)/(Inertial Reference Unit (IRU) can extend the maximum FDE unavailability time based upon the amount of time the system can maintain RNP 4 coasting performance without a position update. The approval must indicate the maximum GNSS FDE unavailability time.
F.4.3 GNSS Eligibility. Aircraft fitted with only GNSS for oceanic and remote continental airspace operations must meet the RNP 4 performance requirements. The acceptable technical standards are:
Appendix F F-4
1. Combination GNSS Navigation Computer/Sensor.
• TSO-C129a Class A and
• TSO-C146( ).
2. Flight management system (FMS) (TSO-C115b or later revision) with GNSS sensor.
• TSO-C129a (Class B or C),
• TSO-C145( ), and
• TSO-C196( ).
Note: GNSS equipment approved under TSO-C129a must also meet AC 20-138( ), Appendix 1.
F.4.3.1 For aircraft equipped with GNSS-only, the operator must have an approved GNSS availability prediction program ensuring the requisite availability of the GNSS FDE function. Prior to conducting RNP 4 operations in oceanic or remote continental areas, the operator must use this prediction program prior to dispatch. When using the prediction program, the maximum predicted, allowable time for a loss of FDE is 25 minutes. When the predicted loss of FDE exceeds 25 minutes, then RNP 4 operations are not available, and the operator must reschedule the flight. All RNP 4 operations approvals must document the 25-minute FDE outage limit as a condition of the operational approval.
F.4.4 Integrating Multisensor Systems. Multisensor navigation systems integrating GNSS with INS must be capable of sustaining ±4 NM lateral TSE and ±4 NM ATRK for 95 percent of the total flight time to meet the RNP 4 performance requirements. There is no requirement to use a dispatch FDE availability prediction program when the operator uses an approved multisensor navigation system that includes INS. The INS must be approved in accordance with Title 14 of the Code of Federal Regulations (14 CFR) part 121, Appendix G.
F.4.5 Demonstrations. Demonstration of aircraft performance in accordance with AC 20-138( ) does not constitute operations approval to conduct RNP operations.
F.5 Maintenance Requirements.
F.5.1 LRNS. Aircraft must have established maintenance procedures for all LRNS intended for use in oceanic and remote continental area operations.
F.6 Functional Requirements of Navigation Data Displays.
F.6.1 Installation. The following navigation displays and functions are required and must be installed in accordance with AC 20-138( ) or equivalent airworthiness installation advisory material.