Appendix 1 Appendix 1. GPS Oceanic/Remote Navigation.
A1-1. GPS Oceanic/Remote Navigation.
a. The following criteria define an acceptable means of compliance for approval of TSO-C129(AR) GPS equipment intended for oceanic and remote operation without reliance on other long-range navigation systems. This approval is granted as a non-TSO function according to existing policy. Equipment that previously demonstrated compliance to Notice 8110.60 or previous revisions of AC 20-138, appendix 1 are still eligible for oceanic and remote operation and do not need re-evaluation.
Note 1: TSO-C129a has been cancelled but equipment with an existing TSO-C129a TSOA may receive approval for oceanic/remote operation without reliance on other long range navigation systems.
Note 2: The FAA has adopted the ICAO term
“oceanic/remote” instead of Class II.
b. TSO-C196(AR) and TSO-C145/C146(AR) equipment are inherently capable of supporting this operation without further evaluation if the operator obtains an FDE prediction program (see paragraph 5-2.3). Equipment manufacturers may choose to provide further robustness for oceanic and remote area operations by including barometric aiding in their FDE algorithms. Appendix G of RTCA/DO-316 and RTCA/DO-229D, Change 1 provide an acceptable barometric aiding implementation method for TSO-C196(AR) and TSO-C145/C146(AR) equipment respectively.
Note: Barometric aiding enables the equipment to continue providing integrity when only four satellites are available for use in the position solution. Appendix G of RTCA/DO-229C for TSO-C145a/C146a equipment is identical to appendix G in RTCA/DO-229D, Change 1.
A1-2. Approval Process
a. TSO Authorization.
The criteria in this appendix are in addition to the TSO-C129(AR) requirements and approved as a non-TSO function. The ACO should issue a separate letter of design approval stating that the equipment (including part number) and software prediction program (including revision number) meet the criteria in this appendix. The applicant should be able to substantiate equivalent performance between the FDE prediction program and the airborne receiver algorithm. See paragraph 5-2.3 for information on FDE prediction program performance.
b. Installation Approval.
(1) The applicant obtains the GPS navigation equipment installation approval.
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Appendix 1
(2) If the equipment manufacturer has previously obtained a letter of design approval as described in paragraph A1-1.a of this appendix, further evaluation as described in paragraphs A1-2 and A1-3 of this appendix is not required.
(3) If the equipment manufacturer has not obtained a letter of design approval, then the applicant must demonstrate compliance with the requirements in paragraphs A1-2.b(4) through A1-3 of this appendix.
(4) The failure of the long-range navigation function is a major 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 oceanic/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 1: The term “primary means” is obsolete. T his updated AFMS/RFMS language is a clarification of previous guidance.
Note 2: The FAA has adopted the ICAO term
“oceanic/remote” instead of Class II.
c. Operational Approval.
The applicant should be aware that an operational approval must be obtained before conducting oceanic/remote navigation. 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 have an existing TSO-C129(AR) TSOA.
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.
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Appendix 1
(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.
(c) Failed exclusion probability. The probability of failed exclusion must 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.
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Appendix 1
(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(AR) and 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.
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Appendix 2 Appendix 2. RNP AR Operations.
A2-1. Introduction.
a. This appendix describes the aircraft performance, functional criteria, and installation considerations for aircraft to qualify for RNP AR approaches. The information presented in this appendix has some necessary changes, mostly due to formatting and grammar, but also provides additional clarification information. This AC will take precedence for aircraft qualification if there are any perceived conflicts with the latest revision of AC 90-101. 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. FAA headquarters retains oversight of all applications for operations approval to conduct RNP AR operations. To avoid delays in processing these operations applications and confirming aircraft qualification, Aircraft Certification field offices should coordinate all RNP AR aircraft qualification airworthiness applications with the Navigation and Flight Technologies section (AIR-131) at FAA headquarters. Coordinating the application with AIR-131 will ensure the aircraft qualification requirements are met and documented in a manner facilitating an applicant's expeditious RNP AR operations approval.
d. The FAA strongly recommends RNP AR airworthiness applicants (i.e., the TC or STC holder) include a deviation alerting function for excess lateral or vertical deviation during RNP AR approach operations. The intent for this function is to prevent controlled flight into terrain or obstacles during RNP AR operations.
Note 1: This recommendation applies whether the aircraft uses baro-VNAV vertical guidance or GPS/SBAS vertical guidance during RNP AR approach operations.
Note 2: Aircraft with existing, approved deviation alerting functions supporting RNP AR approach operations in service prior to 2016 meet the intent of this guidance.
(1) The deviation alerting function need not be accomplished through the aircraft’s GPWS or TAWS equipment, as this may not be practical from a systems engineering perspective. Applicants may base the alert on flight technical error or total system error .
(2) The FAA recommends applicants provide an alert no later than when a A2-1
--- --- Appendix 2 deviation reaches operational deviation limits for RNP AR approach operations. An alert should occur when a glidepath deviation reaches or exceeds 75 feet; or when a lateral deviation reaches or exceeds a distance equivalent to one times the RNP value in use (i.e., 1×RNP).
More conservative alerting schemes are acceptable.
(3) The deviation alert should occur within 10 seconds of reaching a lateral or vertical deviation limit consistent with the RNP AR procedure design assumptions.
(4) The deviation alert may be aural, visual or both. The alert should be easily recognized by the pilot; and, when the implementation uses a visual alert, the visual alert should be in the pilot’s primary field of view.
Note: The airworthiness applicant should be cognizant of the existing alerts on the aircraft when implementing the deviation alerting function. The deviation alerting function should not conflict with existing alerts or cause flight crew human factors issues. The deviation alerting should not supersede and prevent initiation of other mandatory alerting functions.
e. The RNP AR airworthiness applicant (i.e., the TC or STC holder) should consider developing: an operations manual detailing flight crew/pilot procedures for executing RNP AR operations; detailed suggestions on training for RNP AR operations; and any necessary maintenance plan(s) for the aircraft to enable ongoing RNP AR operations. The applicant should complete these concurrent with the airworthiness approval to assist operators with their RNP AR operations approval. Use of these standardized products could streamline the operator’s RNP AR operational approval. See the latest revision of AC 90-101 for operational approval information.
f. 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 defines the path the aircraft must use to evaluate performance. The aircraft’s navigation system will also define the vertical path in the final approach segment by a flight path angle and as a straight line emanating from a fix and altitude.
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Appendix 2
b. Lateral Accuracy.
The navigation system must provide lateral guidance so aircraft remain within the lateral boundaries of the defined RNP AR procedure at one times the RNP value in use (1×RNP, 95%).
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):
ඥ[(6076.115)(1.225)𝑅𝑅𝑅𝑅𝑅𝑅 tan 𝜃𝜃]2 + (60 tan 𝜃𝜃)2 + 752 + [(−8.8 × 10−8)(ℎ + ∆ℎ)2 + (6.5 × 10−3)(ℎ + ∆ℎ) + 50]2 where θ 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) RNP AR 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 A2-3
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.
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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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