Appendix 1
(4) The failure of the long-range navigation function is a m ajor failure condition.
For many oceanic/remote operations, this requires equipping the airplane with at least two (or more) independent (i.e., dual control display unit, dual GPS antenna, dual power sources, dual GPS sensors, etc.) navigation equipment with a mean time between failures of at least 1000 hours each (for dual equipage).
(5) Once the installation has been approved, the AFMS/RFMS should be updated to state: "The XXX GPS equipment as installed has been found to comply with the requirements for GPS Class II oceanic and remote navigation without reliance on other long-range navigation systems when used in conjunction with the XXX prediction program. This does not constitute an operational approval."
Note: The term “primary means” is obsolete. This updated AFMS/RFMS language is a clarification of previous guidance.
c. Operational Approval.
The applicant should be aware that an operational approval must be obtained before conducting Class II navigation (remote/oceanic). Applicants should contact the appropriate flight standards district office to seek operational approval.
A1-3. Equipment Performance.
a. TSO-C129(AR).
The GPS equipment must meet the criteria of TSO-C129(AR).
b. Fault Detection and Exclusion.
(1) The GPS equipment must be able to detect and exclude a GPS satellite failure by means of an FDE algorithm. The exclusion of a satellite failure must be automatic; pilot action is not permitted to accomplish exclusion. Additional augmentations (such as clock aiding or barometric aiding) are not precluded if equipment manufacturers choose to implement these methods to increase FDE robustness. FDE terms are defined in RTCA/DO-316; and, RTCA/DO-316 appendix G provides an acceptable barometric aiding implementation method.
(a) Missed alert probability. The probability of missed alert must be less than or equal to 0.001 for every geometry and every navigation mode. This requirement is on the missed alert rate external to the GPS equipment. When related to the internal algorithm, it includes both probabilities of missed detection and false exclusion.
(b) False alert probability. The probability of false alert must be less than or equal to 0.002/hour. This requirement is on the false alert rate external to the GPS equipment.
When related to the internal algorithm, it includes both probabilities of false detection and the failure to exclude the false detection.
A1-2
Appendix 1
(c) Failed exclusion probability. The probability of failed exclusion m ust be less than or equal to 0.001 for every geometry and every navigation mode for which exclusion is implemented. Exclusion must be implemented for the oceanic mode. This requirement is on the alert rate external to the GPS equipment due to failed exclusion.
(d) Time-to-alert. The time-to-alert for oceanic/remote navigation mode is defined to be at least 30 seconds, but must not exceed 5 minutes.
(2) In addition to FDE, the equipment must use an acceptable means to detect and exclude from the navigation solution any satellite that experiences a failure which causes a pseudorange step. A pseudorange step is a sudden change in the measured distance to a satellite. It can be written as:
PRSTEP = | PRPREDICTED - PRMEASURED |
where PRPREDICTED is the predicted pseudorange at the time of measurement, based on previous measurements, and PRMEASURED is the pseudorange at the time of the measurement.
(a) The equipment must detect a pseudorange step error greater than 1000 meters, including steps that cause loss of lock for less than 10 seconds.
(b) If a pseudorange step is detected for a satellite, that satellite must be excluded from use in the navigation algorithm until its integrity can be verified, and fault detection is available. The equipment manufacturer is free to choose any method to calculate the predicted pseudorange. However, any method used should properly take into account satellite movement and aircraft dynamics up to a groundspeed of 750 knots (kts) and accelerations up to 14.7 meters/second/second (1.5 g's).
(3) The GPS equipment must exclude, without pilot action, any satellite designated unhealthy by any of the GPS navigation data. The satellite must be excluded within 5 minutes of the designation as unhealthy by the satellite. RTCA/DO-316, paragraph 2.1.1.3.2 provides a description of the parameters that must be checked.
(4) If a GPS satellite failure results in loss of GPS navigation (due to the failure to exclude or due to loss of a critical satellite), an appropriate failure indication must be provided to the flight crew.
(5) It is recommended that the equipment provide, upon request, an indication of the current estimate of position uncertainty in nautical miles.
(a) This estimate must be based on measurement inconsistency and must bound the true error with high confidence (approximately 99.9 percent).
(b) This estimate will not be available if there are only four measurements available (because there is no redundancy).
(c) This position uncertainty estimate is equivalent to the Horizontal Uncertainty Level (HUL) that is an optional output for TSO-C196 and A1-3
Appendix 1 A1-4 TSO-C145(AR)/C146(AR) equipment; and, provides the most time for the exclusion algorithm to exclude the failure without increasing the probability of a missed alert.
(d) This output is intended to provide information about the approximate magnitude of a potential positioning failure, when the horizontal protection level exceeds the alert limit or when a positioning failure has been detected, but not excluded.
Appendix 2
Appendix 2. RNP AR Operations.
A2-1. Introductio
n.
a. This appendix describes the aircraft performance, functional criteria, and installation considerations for aircraft to qualify for required navigation performance authorization required approaches. The aircraft qualification information is presented here as a convenient necessary first step to consolidate all the positioning and navigation equipment and RNP AR airworthiness guidance into one AC. The information presented in this appendix has some necessary minor changes due to formatting and grammar along with some additional clarification information. But, the basic information from AC 90-101A has not changed other than to recognize TSO-C196 equipment. The plan is for future AC 90-101 revisions to remove the airworthiness guidance. See the latest revision of AC 90-101 for operational approval guidance information.
b. Applicants may establish compliance with this appendix as part of a type certification or supplemental type certification and document this in the aircraft flight manual (supplement). The TC holder of a previously certified aircraft can document compliance with these aircraft qualification criteria without a new airworthiness project (e.g., without AFM/RFM change), and should advise the appropriate ACO of any new performance the original airworthiness approval did not cover. The AFM/RFM or other aircraft qualification evidence should address: the required modes of operation to fly an RNP AR approach; the normal and abnormal flight crew operating procedures; responses to failure alerts and annunciations; and any other operating limitations.
c. In addition to the specific RNP AR guidance in this appendix, the aircraft’s positioning and navigation system(s) must comply with the applicable chapters in this AC.
A2-2. Performance Requirements.
This paragraph defines the general performance requirements for aircraft qualification.
Paragraphs A2-3, A2-4, and A2-5 of this appendix provide guidance material on an acceptable means of satisfying these requirements.
a. Path Definition.
The published instrument approach procedure and RTCA/DO-236B, paragraph 3.2 define the path the aircraft must use to evaluate performance. The aircraft’s navigation system will also define all vertical paths in the final approach segment by a flight path angle (RTCA/DO-236B, paragraph 3.2.8.4.3) and as a straight line emanating to a fix and altitude.
b. Lateral Accuracy.
The aircraft must comply with paragraph 2.1.1 of RTCA/DO-236B.
A2-1
Appendix 2
c. Vertical Accuracy.
The vertical system error includes altimetry system error (assuming the temperature and lapse rates of the International Standard Atmosphere), the effect of along track error, system computation error, data resolution error, and flight technical error. The 99.7% of system error in the vertical direction must be less than the following (in feet):
22 22 28 36076115 1 225 60 75 88 10 65 10 50.. t a n t a n . .R N P hh hh
where is the vertical navigation path angle, h is the height of the local altimetry reporting station and h is the height of the aircraft above the reporting station.
d. Airspace Containment.
The FAA publishes RNP AR approaches as performance-based approaches. As such, they do not inherently require any specific technology or procedure, but instead require a level of performance.
(1) RNAV and baro-VNAV.
Establishing compliance to a required level of performance can be difficult. This appendix describes an acceptable means of achieving the required navigation performance.
This appendix provides a detailed acceptable means of compliance for aircraft using an RNAV system relying primarily on GNSS and a VNAV system relying on barometric altimetry.
Aircraft complying with this appendix provide the requisite airspace containment.
(2) Other Systems or Alternate Means of Compliance.
The probability of the aircraft exiting the lateral and vertical extent of the obstacle clearance volume must not exceed 10-7 per approach, including the missed approach. An operator may satisfy this requirement through an operational safety assessment applying: (a) appropriate quantitative, numerical methods; (b) qualitative operational and procedural considerations and mitigations; or (c) an appropriate combination of both quantitative and qualitative methods.
Note 1: If the aircraft does not remain within the obstacle clearance volume after annunciating the systems failure, then this requirement applies to the total probability of 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 A2-2
Appendix 2
requirem ent 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-236B. The requirement in RTCA/DO-236B 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.
RTCA/DO-236B provides additional information concerning many of the required functions for RNP AR aircraft qualification.
a. 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 10 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 (GPS/SBAS or GPS/GBAS) 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 countires 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).
A2-3
Appendix 2
Note: GPS-based sensors output an HPL (see RTCA/DO-229D 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 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 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 inertial reference system 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.
A2-4
Appendix 2
(3) DME.
GNSS-updating is the basis for initiating all RNP AR approach procedures. The aircraft m ay 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 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:
82 388 10 65 10 50..ASE H H (ft)
where H is the true altitude of the aircraft.
(7) Temperature compensation systems.
Temperature compensation systems with an airworthiness approval providing corrections to the baro-VNAV guidance must comply with RTCA/DO-236B, appendix H.2.
This criterion applies to the final approach segment. 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.
A2-5
Appendix 2
b. Path Definition and Flight Planning.
(1) Maintaining Track and Leg Transitions.
The aircraft must have th e capability to execute leg transitions and maintain tracks 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-236B 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 4 of this appendix. EUROCAE ED-75A/ RTCA DO-236B 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-236B 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 when there is no requirement for RNP containment.
A2-6
Appendix 2
Turn Height Above Airport (Fee
t) 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
*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 A2-7
Appendix 2
a degree, with com putational 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);
(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 A2-8
Appendix 2
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.
(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 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.
c. Demonstration of Path Steering Performance.
The applicant must complete the demonstration in accordance with AC 120-29 (latest revision), paragraphs 5.19.2.2 and 5.19.3.1 when the demonstration of RNP capability includes a demonstration of the aircraft's path steering performance (i.e., flight technical error).
d. Displays.
(1) Continuous Display of Deviation.
A2-9