Appendix 2 excursion outside the obstacle clearance volume. This includes events caused by latent conditions (integrity) and by detected conditions (continuity). When ensuring the aircraft does not exit the obstacle clearance volume, an analysis of the aircraft performance should consider the monitor limit of the alert, the latency of the alert, the crew reaction time, and any aircraft response to the alert. The requirement applies to a single approach, considering the exposure time of the operation, the navigation aid geometry, and navigation performance available for each published approach.
Note 2: This containment requirement derives from the operational requirement. This requirement is notably different than the containment requirement specified in RTCA/DO-283B and RTCA/DO-236C, Chg 1. The requirement in RTCA/DO-283B and RTCA/DO-236C, Chg 1 facilitates airspace design and does not directly equate to obstacle clearance.
e. System Monitoring.
The critical components of RNP approach procedure implementation are the RNP requirements of the approach, the ability of the aircraft navigation system to monitor its navigation performance, and to alert the pilot when RNP requirements are not being met.
A2-3. RNP AR General Requirements.
The following information reflects required functions for RNP AR aircraft qualification.
a. TAWS.
(1) The aircraft must be equipped with a Class A TAWS to conduct RNP AR operations. The intent is to ensure the flight crew/pilot has the situation awareness benefits Class A TAWS provides.
(2) To continue eligibility for RNP AR operations, the aircraft's TAWS must contain the most current operating software and the most current terrain and obstacle database offered by the TAWS manufacturer. During a formal RNP AR aircraft qualification airworthiness project, the aircraft manufacturer should establish continuing airworthiness procedures requiring the aircraft operator to keep both the TAWS operating software and the TAWS onboard terrain and obstacle database current. When these procedures are not part of the aircraft manufacturer’s documented RNP AR qualification, the operator must establish procedures to keep the TAWS operating software and terrain and obstacle database current.
The operator should include these procedures in their operational application to conduct RNP AR operations.
A2-4
Appendix 2 Note: The intent behind this paragraph is to install updates that correct software deficiencies affecting the TAWS intended function and airworthiness. There is no intent to force installation of new functions or features.
(3) The position solution for the TAWS must be sourced directly from a GNSS sensor or a tightly-coupled GNSS/inertial system without any reference to or interchange with the RNP equipment’s (e.g., FMS) position solution output.
Note: There is no intent to exclude a Kalman-filtered position solution taken directly from a tightly-coupled GNSS/inertial sensor.
(4) The TAWS should use altitude that is compensated for local pressure and temperature effects (e.g., corrected barometric or Global Navigation Satellite System (GNSS) altitude). The altitude compensation should not require flight crew/pilot action or input and must not impact the primary barometric altimeter system’s function.
b. Position Estimation.
The navigation system must estimate the aircraft’s position. This appendix identifies unique issues for the navigation sensors within the context of RNP AR instrument approaches.
(1) GNSS.
(a) The GNSS sensor must comply with the guidelines in chapter 5 of this AC.
The total system accuracy analysis may use the following sensor accuracies without additional substantiation: GPS sensor accuracy better than 36 meters (95%), and augmented GPS/SBAS sensor accuracy is better than 2 meters (95%).
Note: Sensors processing other GNSS’ may also be able to provide similar or better accuracies without further substantiation. This guidance can be updated once countries with other GNSS’ provide an assured statement of operational system accuracy.
(b) In the event of a latent GNSS satellite failure and marginal GNSS satellite geometry (e.g., horizontal protection level (HPL) equal to the horizontal alert limit (HAL) or vertical protection level (VPL) equal to the vertical alert limit (VAL)), the probability the total system error remains within the procedure design obstacle clearance volume must be greater than 95% (both laterally and vertically).
Note: GPS-based sensors output an HPL (see RTCA/DO-229D, Change 1 for definition) that is sometimes referred to as horizontal integrity limit (HIL).
The HPL is a measure of the position estimation error assuming a latent failure is present. In lieu of a detailed A2-5
Appendix 2 analysis of the effects of latent failures on the total system error, an acceptable means of compliance for GPS-based systems is to ensure the HPL remains less than twice the RNP value, minus the FTE 95%, (i.e. HPL < ((2*RNP) FTE 95%)) during the RNP AR approach operation.
(c) A TSO-C145(AR) Class 3 sensor may be used for linear (or angular) vertical guidance. The GPS/SBAS sensor must be within the GPS/SBAS service volume and in an integrity mode that outputs a GPS/SBAS-generated VPL.
Note 1: The navigation computer will adjust the HPL according to its mode. One acceptable integration is using the KH constant (described in RTCA/DO-229D, Change 1, appendix J) on the interface bus for adjusting the HPL if the sensor provides a KH output.
Note 2: GPS/SBAS vertical guidance with a 50m VAL has been shown to be consistent with the required total system performance for operations down to RNP 0.23. A 35m VAL is consistent with required performance for operations down to RNP 0.1. These values were validated through FAA technical analysis and flight test. The use of these values requires no further navigation system substantiation.
Note 3: Using GPS/SBAS vertical guidance precludes the need for independent monitoring as prescribed by AC 90-101 (latest revision), appendix 4, paragraph 3.h.
(2) IRS.
An IRS must satisfy the criteria of 14 CFR part 121, appendix G. While appendix G defines the requirement for a 2 NM per hour drift rate (95%) for flights up to 10 hours, this rate does not apply to an RNAV system after loss of position updating. Applicants may assume an IRS demonstrating compliance with 14 CFR part 121, appendix G experiences an initial drift rate of 4 NM for the first 30 minutes (95%) without further substantiation. However, aircraft manufacturers and applicants can choose to demonstrate better inertial performance.
Note: Integrated GNSS/IRU position solutions reduce the rate of degradation after loss of position updating. For “tightly coupled” GNSS/IRU’s, RTCA/DO-229D, appendix R, provides additional guidance.
(3) DME.
GNSS-updating is the basis for initiating all RNP AR approach procedures. The aircraft may use DME/DME-updating as a reversionary navigation mode during an RNP AR approach or missed approach when the navigation system continues to comply with the A2-6
Appendix 2 required RNP value. The applicant should also identify any requirements for the DME infrastructure and/or any necessary operational procedures and limitations to conduct an RNP AR approach procedure through aircraft position updating using DME/DME.
(4) VOR.
The aircraft's RNAV system may not use VOR-updating when conducting public RNP AR instrument approach procedures. The applicant should identify any constraints on the VOR infrastructure or the procedure for a given aircraft to comply with this requirement.
Note: This paragraph does not imply an equipment capability must exist providing a direct means of inhibiting VOR updating. An operational procedure requiring the flight crew to inhibit VOR-updating or a procedure requiring the flight crew to execute a missed approach upon annunciation of reversion to VOR-updating may meet this requirement.
(5) Multi-Sensor Systems.
For multi-sensor systems, there must be automatic reversion to an alternate RNAV sensor if the primary RNAV sensor fails. There need not be automatic reversion from one multi-sensor system to another multi-sensor system.
(6) Altimetry System Error.
The 99.7% aircraft altimetry system error for each aircraft (assuming the temperature and lapse rates of the International Standard Atmosphere) must be less than or equal to the following with the aircraft in the approach configuration:
𝐴𝐴𝐴 = −8.8 ∗ 10−8 ∗ 𝐻2 + 6.5 ∗ 10−3 ∗ 𝐻 + 50 (ft) where H is the true altitude of the aircraft.
(7) Temperature Compensation Systems.
Temperature compensation systems with an airworthiness approval providing automatic corrections to the baro-VNAV guidance must comply with RTCA/DO-283B, appendix H. The applicant should document compliance to this standard to allow the operator to conduct RNP approaches when the actual temperature is below or above the published procedure temperature design limits.
c. Path Definition and Flight Planning.
(1) Maintaining Track and Leg Transitions.
The aircraft must have the capability to execute leg transitions and maintain tracks A2-7
Appendix 2 consistent with the following paths:
(a) A geodesic line between two fixes (TF);
(b) A direct path to a fix (DF);
(c) A specified track to a fix, defined by a course (CF), and
(d) A specified track to an altitude (FA).
Note 1: Industry standards for these paths can be found in RTCA/DO-283B, and ARINC Specification 424, which refer to them as TF, DF, CF, and FA path terminators.
Also, certain procedures require RF legs as described in paragraph A2-4 and appendix 3. ED-75, RTCA/DO-236C Chg 1, RTCA/DO-283B, and ED-77/RTCA DO-201A describe the application of these paths in more detail.
Note 2: The navigation system may accommodate other ARINC 424 path terminators (e.g., heading to manual terminator (VM)); and the missed approach procedure may use these types of paths when there is no requirement for RNP containment.
(2) Fly-By and Fly-Over Fixes.
The aircraft must have the capability to execute fly-by and fly-over fixes. For fly-by turns, the navigation system must limit the path definition within the theoretical transition area defined in RTCA/DO-236C, Chg 1 and RTCA/DO-283B under the wind conditions identified in Table 11. Since the fly-over turn is not compatible with RNP flight tracks, an RNP AR procedure design will use a fly-over turn at a fix only when there is no requirement for RNP containment.
Note: The RTCA documents do not address fly-over fix theoretical transition area since there is no requirement for RNP containment. Fly-over fixes are addressed in TSO-C115d, appendix 1.
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Appendix 2 Turn Height Above Airport (Feet) Standard Tailwind Component (Knots)* 500 25 Standard AFS-400 Approval 1,000 37.5 30 1,500 50 35 2,000 50 40 2,500 50 45 3,000 50 3,500 55 4,000 60 4,500 65 5,000 70 5,500 75 6,000 80 6,500 85 7,000 90 7,500 95 8,000 100 8,500 105 9,000 110 9,500 115 10,000 120 10,500 125 ≥11,000 130 Table 11. Tailwind Component (VKTW) for Turn Calculations A2-9
Appendix 2 *Other tailwind gradients may be used after a site-specific determination of wind based on that location’s meteorological history (using available information from other sources). Document the source and value used on the procedure form (the FAA uses Form 8260-9).
Note: A new tailwind component may be interpolated for turns initiated at an altitude located between the values in Table 11. The 0 ft value for wind is 15 knots if an interpolated value is ever used below 500 ft.
(3) Waypoint Resolution Error.
The navigation database must provide sufficient data resolution to ensure the navigation system achieves the required accuracy. Waypoint resolution error must be less than or equal to 60 feet, including both the data storage resolution and the RNAV system computational resolution used internally for flight plan waypoint construction. The navigation database must contain vertical angles (flight path angles) stored to a resolution of hundredths of a degree, with computational resolution such that the system-defined path is within 5 feet of the published path.
(4) Capability for a “Direct-To” Function.
The navigation system must have a “Direct-To” function the flight crew can activate at any time. This function must be available to any fix. The navigation system must also be capable of generating a geodesic path to the designated “To” fix, without “S-turning” and without undue delay.
Note: The applicant should identify any limitations associated with the operational use of the aircraft navigation system’s “Direct-To” functions. For example, if there are limitations associated with intercepting an RF leg segment, then the flight manual or aircraft qualification guidance should identify those limitations.
(5) Capability to Define a Vertical Path.
The navigation system must be capable of defining a vertical path by a flight path angle to a fix. The system must also be capable of specifying a vertical path between altitude constraints at two fixes in the flight plan. The navigation system must also define fix altitude constraints as one of the following:
(a) An “AT or ABOVE” altitude constraint (for example, 2400A, may be appropriate for situations where bounding the vertical path is not required);
A2-10
Appendix 2
(b) An “AT or BELOW” altitude constraint (for example, 4800B, may be appropriate for situations where bounding the vertical path is not required);
(c) An “AT” altitude constraint (for example, 5200); or
(d) A “WINDOW” constraint (for example, 2400A3400B).
(6) Altitudes and/or Speeds.
The navigation system must extract the altitudes and/or speeds defined in published terminal procedures from the onboard navigation database.
(7) Path Construction.
The navigation system must be able to construct a path to provide guidance from the current position to a vertically constrained fix.
(8) Capability to Load Procedures from the Navigation Database.
The navigation system must have the capability to load the entire procedure(s) to be flown into the RNAV system from the onboard navigation database. This includes the approach (including vertical angle), the missed approach, and the approach transitions for the selected airport and runway.
(9) Means to Retrieve and Display Navigation Data.
The navigation system must provide the ability for the flight crew to verify the procedure to be flown through review of the data stored in the onboard navigation database.
This includes the ability to review the data for individual waypoints and for navigation aids.
(10) Magnetic Variation.
For paths defined by a course (CF and FA path terminators), the navigation system must use the magnetic variation value for the procedure in the navigation database. The navigation database must accurately represent the procedure as promulgated by the procedure designer, including the magnetic variation used in the procedure design.
Note: The above guidance is for using magnetic variation in the navigation computer for path generation.
(11) Changes in RNP Value.
RNP changes to lower RNP values must be complete by the first fix defining the leg with the lower RNP value. Any operational procedures necessary to meet this requirement must be identified.
Note: One acceptable means to meet this requirement may A2-11
--- Appendix 2 be to require the flight crew to manually set the lowest RNP value the RNP AR procedure uses before commencing the procedure (i.e., prior to the initial approach fix).
(12) Automatic Leg Sequencing.
The navigation system must provide the capability to automatically sequence to the next leg and display the sequencing to the flight crew in a readily visible manner.
(13) Altitude Restriction Display.
A display of the altitude restrictions associated with flight plan fixes must be available to the pilot. If there is an RNP AR procedure with a flight path angle associated with any flight plan leg, the equipment must display the flight path angle for that leg.
d. Flight Technical Error.
The applicant must confirm ability to maintain FTE (95 percent of the flying time) during straight and curved path segments (see paragraph 17-2).
e. Displays.
(1) Continuous Display of Deviation.
(a) The navigation system must provide the capability to continuously display to the pilot flying, on the primary flight instruments for navigation of the aircraft, the aircraft position relative to the RNAV defined path (both lateral and vertical deviation). The display must allow the pilot to readily distinguish if the cross-track deviation exceeds the RNP value (or a smaller value) or if the vertical deviation exceeds 75 feet (or a smaller value).
(b) The aircraft should have an appropriately-scaled, non-numeric deviation display (i.e., lateral deviation indicator and vertical deviation indicator) in the pilot’s primary optimum field of view. A fixed-scale CDI is acceptable as long as the CDI demonstrates appropriate scaling and sensitivity for the intended RNP value and operation. With a scalable CDI, the scale should derive from the selection of RNP, and should not require the separate selection of a CDI scale. Alerting and annunciation limits must also match the scaling values.
If the equipment uses default RNP values to describe the operational mode (e.g., enroute, terminal area and approach), then displaying the operational mode is an acceptable means from which the flight crew may derive the CDI scale sensitivity.
(c) In lieu of appropriately scaled lateral and vertical deviation indicators in the pilot’s primary optimum field of view, a numeric display of deviation may be acceptable depending on the flight crew workload and the numeric display characteristics.
A2-12
Appendix 2
(2) Identification of the Active (TO) Waypoint.
The navigation system must provide a display identifying the active waypoint either in the pilot’s primary optimum field of view, or on a readily accessible and visible display to the flight crew.
(3) Display of Distance and Bearing.
The navigation system must provide a display of distance and bearing to the active (TO) waypoint in the pilot’s primary optimum field of view. Where not viable, a readily accessible page on a control display unit, readily visible to the flight crew, may display the data.
(4) Display of Groundspeed and Time.
The navigation system must provide the display of groundspeed and time to the active (TO) waypoint in the pilot’s primary optimum field of view. Where not viable, a readily accessible page on a control display unit, readily visible to the flight crew, may display the data.
(5) Display of TO/FROM the active waypoint.
The navigation system must provide a TO/FROM display in the pilot’s primary optimum field of view.
Note: See paragraph 8-3.g(2) for TO/TO navigation computer displays.
(6) Desired Track Display.
The navigation system must have the capability to continuously display to the pilot flying the aircraft the RNAV desired track. This display must be on the primary flight instruments for aircraft navigation.
(7) Display of Aircraft Track.
The navigation system must provide a display of the actual aircraft track (or track angle error) either in the pilot’s primary optimum field of view or on a readily accessible and visible display to the flight crew.
(8) Failure Annunciation.
The aircraft must provide a means to annunciate failures of any aircraft component of the RNAV system, including the navigation sensors. The annunciation must be visible to the pilot and located in the primary optimum field of view.
A2-13
Appendix 2
(9) Slaved Course Selector.
The navigation system must provide a course selector automatically slaved to the RNAV computed path.
(10) RNAV Path Display.
Where the minimum flight crew is two pilots, the navigation system must provide a readily visible means for the pilot monitoring to verify the aircraft’s RNAV defined path and the aircraft’s position relative to the desired path.
(11) Display of Distance to Go.
The navigation system must provide the ability to display distance to go to any waypoint selected by the flight crew.
(12) Display of Distance Between Flight Plan Waypoints.
The navigation system must provide the ability to display the distance between flight plan waypoints.
(13) Display of Deviation.
The navigation system must provide a numeric display of the vertical deviation with a resolution of 10 feet or less, and the lateral deviation with a resolution of 0.01 NM or less.
(14) Display of Barometric Altitude.
The aircraft must display barometric altitude from two independent altimetry sources, one in each pilots’ primary optimum field of view to support an operational cross check of altitude sources.
Note 1: If the aircraft includes the ability to automatically compare the output of the independent altitude sources, including independent aircraft static air pressure systems, and the aircraft can provide an alert in the pilot’s primary optimum field of view when deviations between the sources exceed ±100 feet, then the applicant should document this comparator monitoring function in the AFM/RFM or aircraft qualification guidance.
Note 2: As stated in paragraph A2-3.b(1)(c) note 3 of this appendix, using GPS/SBAS vertical guidance precludes the need for independent monitoring as prescribed by AC 90-101 (latest revision), appendix 4, paragraph 3.h.
A2-14
Appendix 2
(15) Display of Active Sensors.
(a) The aircraft must display the current navigation sensor(s) in use. The aircraft should provide this display in the primary optimum field of view.
Note: Flight crew procedures may mitigate the need for this display if the applicant and/or operator can demonstrate the flight crew workload is acceptable.
(b) In-service aircraft that do not display the current navigation sensor in use may still be eligible for RNP AR approach operations. To be eligible, the aircraft manufacturer must demonstrate continued RNP AR approach performance when GNSS is lost (for example, through inertial navigation) and continue to monitor/annunciate loss of RNP capability (i.e., annunciating “Unable RNP”). Since the loss of GNSS is unlikely:
(i) The aircraft performance must show the conditional probability the aircraft exits the final approach obstacle clearance volume is less than 0.001 (one in a thousand). This ensures that 999 times out of 1000 the aircraft can complete an RNP AR approach when a loss of GNSS occurs.
(ii) To support execution of the missed approach procedure, the aircraft performance must show the conditional probability the aircraft exits the missed approach obstacle clearance volume is less than 0.01 (one in a hundred). This will ensure that 99 times out of 100 the aircraft can complete a missed approach procedure from the lowest minimums following loss of GNSS.
Note 1: Executing a missed approach is unlikely given the weather condition requirements to begin an RNP AR approach procedure. Therefore, the conditional probability requirement for the procedure’s missed approach is less stringent than the performance requirement for the procedure’s final approach segment.
Note 2: The aircraft manufacturer may conduct the aircraft performance demonstration through laboratory and simulation analysis. Flight test data collection and demonstration in the actual aircraft is not required.
f. Hazard Affects.
(1) The system must be consistent with at least a major failure condition for the display of misleading lateral or vertical guidance on an RNP AR approach.
(2) The system must be consistent with at least a major failure condition for the loss of lateral guidance and a minor failure condition for loss of vertical guidance on an RNP AR A2-15