Advisory U.S. Department of Transportation Circular Federal Aviation Administration Subject: Airworthiness Approval of Date: 4/7/16 AC No: 20-138D Positioning and Navigation Systems Initiated by: AIR-130 Change: 2
1. Purpose. Change 2 adds additional information and clarifications to AC 20-138D, Change 1 along with minor updates.
2. Principal Changes. The page control chart indicates which pages have changed.
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137 142 A1-1-A1-2 A2-1-A2-5 A2-7-A2-8 A2-12 A2-15 A3-1-A3-7 A7-13-A7-14 A7-17-A7-18 A8-1-A8-2 A10-1 Susan J. M. Cabler 10/10/14 137 4/7/16 10/10/14 142 4/7/16 10/10/14 A1-1-A1-2 4/7/16 10/10/14 A2-1-A2-5 4/7/16 10/10/14 A2-7-A2-8 4/7/16 10/10/14 A2-12 4/7/16 10/10/14 A2-15 4/7/16 10/10/14 A3-1-A3-6 4/7/16 10/10/14 A7-13-A7-14 4/7/16 10/10/14 A7-17-A7-18 4/7/16 10/10/14 A8-1-A8-2 4/7/16 10/10/14 A10-1 4/7/16 Acting Manager, Design, Manufacturing, & Airworthiness Division Aircraft Certification Service ii
Acting Manager , De ign, Manufacturing , & Airworthiness Division Aircraft Cert ificat ion rv1ce Advisory U.S. Department of Transportation Circular Federal Aviation Administration Subject: Airworthiness Approval of Date: 10/10/14 AC No: 20-138D Positioning and Navigation Systems Initiated by: AIR-130 Change: 1 Positioning and navigation equipment may be used for a variety of functions such as navigation, automatic dependent surveillance, and/or terrain awareness and warning systems. This AC addresses the following avionics:
• Global positioning system (GPS) equipment including those using GPS augmentations.
• Area navigation (RNAV) equipment integrating data from multiple navigation sensors.
• RNAV equipment intended for required navigation performance (RNP) operations.
• Baro-VNAV equipment.
This AC does not address new satellite constellations that are planned or currently under construction. This AC will be updated when sufficient documentation is available from the GNSS provider countries and RTCA to support service definition, service performance commitments, and minimum operational performance standards for multi-constellation equipment.
Table of Contents
Chapter 1. General Information1
1-1. Purpose1
1-2. Audience2
1-3. Cancellation2
1-4. Frequently Asked Questions3
Chapter 2. Technical Standard Order Authorization (TSOA) and Airworthiness Approval
Considerations - General10
2-1. Guidance for TSOA/Letter of Design Approval (LODA) and Airworthiness
Approvals10
2-2. TSOA10
2-3. STC-Approved Model List (AML)11
2-4. Type Certificate11
Chapter 3. TSO Authorization12
3-1. TSO-C196(AR)12
3-2. TSO-C145(AR)/C146(AR)13
3-3. TSO-C161a/C162a14
3-4. TSO-C115(AR)15
3-5. TSO-C204/C205/C20618
3-6. Multiple TSO Authorizations19
Chapter 4. Equipment Performance - Advisory Vertical Guidance21
4-1. Introduction21
4-2. Implementations21
4-3. Limitations24
Chapter 5. Equipment Performance - GNSS26
5-1. Introduction26
5-2. GPS (TSO-C129(AR) and TSO-C196(AR) receivers)27
5-2.1 Antennas27
5-2.2 Sensors28
5-2.3 Prediction Program29
5-3. GPS/SBAS (TSO-C145/C146(AR) receivers)31
5-3.1 Antenna31
5-3.2 Sensor and Sensor/Navigation Computer Configuration31
5-3.3 Navigation Database - Data Conversion for GPS/SBAS LNAV/VNAV
Approaches33
5-4. GPS/GBAS (TSO-C161a/C162a receivers)33
5-4.1 Antennas33
5-4.2 VH F D
ata Broadcast Receiving Equipment (TSO-C162a)34
5-4.3 Sensor/Navigation Computer (TSO-C161a)34
5-5. GNSS Upgrades35
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5-5.1 Adding Additional GNSS Equipment35
5-5.2 Replacing GNSS Equipment35
5-5.3 GPS/SBAS Upgrade36
5-5.4 GNSS Antenna Re-Use/Replacement36
5-5.5 Marking38
5-6. Navigation Database38
5-6.1 Database Installation Instructions38
5-6.2 Database Process38
5-7. GNSS Geometric Altitude39
5-8. Terrain Awareness and Warning System (TAWS)39
Chapter 6. Equipment Performance - RNAV Multi-Sensor Equipment40
6-1. Introduction40
6-2. Navigation Database40
6-2.1 Database Installation Instructions40
6-2.2 Database Process40
6-3. GNSS40
6-4. DME/DME41
6-4.1 Reasonableness Checks45
6-4.2 Performance Confirmation45
6-4.3 Multi-Sensor System FMS46
6-5. VOR/DME47
6-6. INS/IRU49
6-7. INS/IRU – GNSS Integration50
6-8. INS/IRU - DME/DME Integration51
Chapter 7. Equipment Performance - RNP (General)53
7-1. Introduction53
7-2. Special Characteristics of RNP Instrument Approaches55
7-3. Special Characteristics of RNP 1.0 and RNP 2.0 Operations55
Chapter 8. Equipment Performance - RNP Approach56
8-1. Introduction56
8-2. Aircraft and System Criteria56
8-3. Performance and Functional Criteria for RNP Systems57
8-4. System Eligibility and Approval for RNP APCH Operations62
Chapter 9. Equipment Performance - RNP Enroute and Terminal63
9-1. I
ntroduction63
9-2. Aircraft and System Criteria for RNP 2.0 and RNP 1.063
9-3. Performance and Functional Criteria65
9-4. System Eligibility and Approval for RNP 2.0 and RNP 1.0 Operations69
9-5. Rotorcraft Enroute, Terminal, and Offshore RNP 0.369
9-5.1 Introduction69
9-5.2 Rotorcraft and System Eligibility for Rotorcraft Enroute RNP 0.3 Operations69
9-5.3 Performance and Functional Criteria70
9-5.4 Approval for Rotorcraft RNP 0.3 Operations74
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Chapter 10. Equipment Performance – RNP Oceanic75
10-1. Introduction75
10-2. Aircraft and System Criteria for RNP 1075
10-2.1 Performance Criteria75
10-2.2 System Criteria76
10-2.3 System Eligibility and Approval for RNP 10 Operations79
10-3. Aircraft and System Criteria for RNP 4.080
10-3.1 Performance and Functional Criteria for RNP 4.080
10-3.2 System Eligibility and Approval for RNP 4.0 Operations85
Chapter 11. Equipment Performance - Baro-VNAV86
11-1. General Limitations for Operations under IFR86
11-2. Baro-VNAV Equipment Performance for Operations under IFR87
Chapter 12. General Installation Considerations93
12-1. Introduction93
12-2. Failure Classification93
12-3. Software Considerations94
12-4. Hardware Considerations94
12-5. Installed Equipment Compatibility95
12-6. Installation Instructions95
12-7. Equipment Capability and Installed Limitations95
12-8. Final Approach Segm ent Step-Down Fixes in Navigation Databases96
12-9. Magnetic Variation Data and Onboard Database98
12-10. Environmental Considerations99
12-11. General Human Factors Considerations99
12-12. Path Definition and Collocated Navigation Aids102
12-13. Runway Position Monitoring103
Chapter 13. General Installation Considerations - Antennas104
13-1. Antenna Placement104
13-1.1 GNSS-Specific Considerations104
13-1.2 General Considerations105
13-2. Anti-Ice Protection105
13-3. Antenna Cables105
13-4. Structure105
13-5. Additional Guidance106
Chapter 14. General Installation Considerations - Sensors107
14-1. Introduction107
14-2. Positioning and Navigation Configuration Strapping107
14-3. Navigation Source Selection107
14-4. Dual Positioning and Navigation Installations108
14-5. Intermixing RNAV equipment108
14-6. Interface to FGS109
14-7. I
nterface to Magnetic/True Switch111
14-8. I
nterface to Air Data and Inertial Reference Systems111
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14-9. Antenna/Sensor Compatibility111
14-10. Interference - Electromagnetic Compatibility (EMC)112
14-11. Interface Requirements113
Chapter 15. Installation Considerations - GNSS114
15-1. Introduction114
15-2. Navigation Displays114
15-3. Failure Indications116
15-4. Documenting Effects of GNSS Outage116
15-5. Installed Performance Capability117
15-6. GPS Equipment117
15-7. GPS/SBAS Equipment118
15-7.1 Limitations118
15-7.2 LP Approach119
15-7.3 Update Rate119
15-7.4 Performance Monitoring119
15-7.5 System Status120
15-7.6 Annunciations120
15-7.7 Accessibility121
15-7.8 GPS/SBAS Glidepath Low Deviation Alerting Function121
15-8. GPS/GBAS VDB Receiver121
15-8.1 Interference – EMC122
15-8.2 Compatibility with Other Systems122
15-8.3 VDB Aircraft Implementation Loss122
15-9. GPS/GBAS Navigation Computer Receiver122
15-9.1 GPS/GBAS Equipment Intended for Category I123
15-9.2 GPS/GBAS Stand-Alone or MMR Equipment Intended for Category I123
15-9.3 Performance and Performance Monitoring124
15-9.4 Integrity124
15-9.5 Continuity of Navigation125
15-9.6 Fault Detection and Annunciation125
15-9.7 System Status125
15-9.8 Annunciation125
15-9.9 Accessibility126
15-9.10 Glidepath Capture126
15-9.11 Equipment Qualification126
15-9.12 Interoperability127
15-9.13 GPS/GBAS Glidepath Low Deviation Alerting Function127
15-10. Special Use Mission Equipment - Not for Navigation127
Chapter 16. Installation Considerations - RNAV Multi-Sensor Equipment128
16-1. Introduction128
16-2. Interface to Primary Navigation Display128
16-2.1 Non-numeric Deviation Displays129
16-2.2 Map Displays129
16-3. Interface to Remote Annunciator129
16-4. Unique Software Considerations130
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16-5. Installed Performance Capability131
Chapter 17. Installation Considerations - RNP132
17-1. Introduction132
17-2. Flight Technical Error132
17-3. Radius to Fix (RF) Legs133
17-4. Interface to FGS133
Chapter 18. Installation Considerations - Baro-VNAV134
18-1. Failure Protection134
18-2. Manufacturer’s Instructions134
18-3. Annunciations134
18-4. Software Changes135
18-5. Integration with GNSS-Provided Vertical Guidance135
18-6. Glidepath Low Deviation Alerting Function137
Chapter 19. Installed Performance - Data Submittal138
19-1. Introduction138
19-2. Project Specific Certification Plan138
19-3. TSO Technical Data138
19-4. Review the installation manual139
19-5. Structural Analysis139
19-6. Power Supply140
19-7. Environment140
19-8. Database140
19-9. Operations manual or AFMS/RFMS140
19-10. Stand-Alone Navigation Equipment141
19-11. Ground and Flight Test Plans (functional and EMI/EMC testing)141
Chapter 20. Installed Performance - Test (General)142
20-1. Intended Function142
20-2. Power Supply142
20-3. Accuracy142
20-4. Human Factors142
Chapter 21. Installed Performance - Test (GNSS)143
21-1. Ground Test - GPS, GPS/SBAS, and GPS/GBAS143
21-1.1 Interference143
21-1.2 Antenna to Aircraft Navigation Reference Offset143
21-1.3 Sensor Installation144
21-1.4 Stand-Alone Navigation Equipment Installation144
21-2. Flight Test - GPS, GPS/SBAS, and GPS/GBAS144
21-2.1 Equipment Installation144
21-2.2 LP/LPV, LPV and GLS145
21-2.3 GPS/GBAS VDB Receiver Installation146
Chapter 22. Installed Performance - Test (RNAV Multi-Sensor Equipment)147
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22-1. Ground Test147
22-2. Flight Test147
22-2.1 Interface to FGS149
22-2.2 GNSS Precision Approach149
Chapter 23. Installed Performance - Test (Baro-VNAV)150
23-1. Introduction150
23-2. Ground Test150
23-2.1 Lab/Bench Tests and Equipment Data Evaluation150
23-2.2 Aircraft Installation Data Evaluation150
23-3. Flight Test151
23-3.1 Functional Flight Test151
23-3.2 Navigation Error Flight Test152
23-4. Follow-on Approval153
Appendix 1. GPS Oceanic/Remote NavigationA1-1
A1-1. GPS Oceanic/Remote NavigationA1-1
A1-2. Approval ProcessA1-1
A1-3. Equipment PerformanceA1-2
Appendix 2. RNP AR OperationsA2-1
A2-1. IntroductionA2-1
A2-2. Performance RequirementsA2-2
A2-3. RNP AR General RequirementsA2-4
A2-4. Requirements for RNP AR Approaches with RF LegsA2-16
A2-5. Requirements for RNP AR Approach values less than 0.3A2-17
A2-6. Requirements for Approaches with a Missed Approach Segment Less Than RNP 1.0.A2-18
A2-7. Navigation Data Validation ProgramA2-20
A2-8. Installation Considerations for RNP ARA2-23
Appendix 3. Advanced RNP FunctionsA3-1
A3-1. IntroductionA3-1
A3-2. Radius to Fix Leg CapabilityA3-2
A3-3. Parallel OffsetsA3-5
A3-4. RNAV HoldingA3-6
A3-5. Scalable RNPA3-6
A3-6. Fixed Radius TransitionsA3-7
A3-7. Time of Arrival ControlA3-7
Appendix 4. GNSS Tests to Support ADS-BA4-1
A4-1. IntroductionA4-1
A4-2. Velocity Accuracy and Velocity Figure of Merit TestsA4-1
A4-3. Horizontal Velocity Accuracy Test Conditions Commens urate with NACV = 1A4-2
A4-4. Horizontal Accuracy Pass/Fail DeterminationA4-4
A4-5. Horizontal Velocity Figure of Merit Pass/Fail DeterminationA4-4
A4-6. Vertical Velocity Accuracy Test Conditions Commensurate with NACV = 1A4-5
A4-7. Vertical Velocity Accuracy Pass/Fail DeterminationA4-7
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A4-8. Vertical Velocity Figure of Merit Pass/Fail DeterminationA4-7
A4-9. Additional Test s to Demonstrate Accuracy Commensurate with NACV = 2A4-8
A4-10. Test to Demonstrate HAE Output and Vertical Position Accuracy MetricA4-8
A4-11. Test to Demonstrate Horizontal Position Accuracy MetricA4-9
A4-12. Demonstrating True Track Angle/True Track Angle ValidityA4-11
Appendix 5. Sample Airplane/Rotorcraft Flight Manual SupplementA5-1
A5-1. IntroductionA5-1
A5-2. Sample AFM(S)/RFM(S) PBN Capabilities and Qualification BasisA5-9
Appendix 6. Installation of GNSS Equipment for VFR Use OnlyA6-1
A6-1. IntroductionA6-1
A6-2. GeneralA6-1
A6-3. ApplicabilityA6-1
A6-4. Technical InstructionsA6-1
Appendix 7. RF leg Demonstration TemplatesA7-1
A7-1. IntroductionA7-1
A7-2. Test Procedures DescriptionA7-3
A7-2.1. DeparturesA7-3
A7-2.2. ArrivalA7-5
A7-2.3. ApproachesA7-7
A7-3. Test GuideA7-15
A7-3.1. Initial Set-UpA7-16
A7-3.2. Airborne Test ConditionsA7-17
Appendix 8. non-U.S. Constellations with GPS-Based GNSSA8-1
A8-1. IntroductionA8-1
Appendix 9. Definitions and AcronymsA9-1
A9-1. DefinitionsA9-1
A9-2. AcronymsA9-3
Appendix 10. Related DocumentsA10-1
A10-1. FAA Advisory CircularsA10-1
A10-2. FAA Technical Standard OrdersA10-3
A10-3. RTCA, Inc. Documents (RTCA/DO) documentsA10-4
A10-4. Other DocumentsA10-6
A10-5. How to Get Related DocumentsA10-6
List of Tables
Table 1. Effective Noise Density for All GNSS Sources26
Table 2. Acceptable Standard Antennas37
Table 3. DME Usable Range43
Table 4. 2D Accuracy Requirements for Equipment Using a Single Co-located VOR/DME48
Table 5. Error Elements49
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Table 6. Vertical Path Performance Limit for Baro-VNAV88
Table 7. Vertical Path Deviations89
Table 8. Typical Hazard Classifications93
Table 9. RNP FTE Performance132
Table 10. INS/IRU Accuracy After Loss of Radio Updating148
Table 11. Tailwind Component (VKTW) for Turn CalculationsA2-9
Table 12. Platform Dynamics for Horizontal Velocity Accuracy TestA4-3
Table 13. Platform Dynamics for Vertical Velocity Accuracy TestA4-6
Table 14. Alpha Departure WaypointsA7-4
Table 15. Bravo Departure WaypointsA7-5
Table 16. Arrival WaypointsA7-7
Table 17. Approach 1 WaypointsA7-9
Table 18. Approach 1 Vertical Error BudgetA7-9
Table 19. Approach 2 WaypointsA7-11
Table 20. Approach 2 Vertical Error BudgetA7-11
Table 21. Approach 3 WaypointsA7-13
Table 22. Approach 3 Vertical Error Budget7-13
Table 23. Approach 4 Waypoints7-15
List of Figures
Figure 1. RNAV Depiction6
Figure 2. RNP Depiction7
Figure 3. Minimum Straight Path Before DAA2-20
Figure 4. Example Procedure ProfilesA7-2
Figure 5. Alpha DepartureA7-4
Figure 6. Bravo DepartureA7-5
Figure 7. ArrivalA7-6
Figure 8. Approach 1A7-8
Figure 9. Approach 2A7-10
Figure 10. Approach 3A7-12
Figure 11. Approach 4A7-14
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-- Chapter 1. General Information.
1-1. Purpose.
This advisory circular (AC) provides guidance material for the airworthiness approval of installed positioning and navigation equipment. Positioning and navigation equipment may be used for a variety of functions such as navigation, automatic dependent surveillance, and/or terrain awareness and warning systems. This AC addresses the following equipment:
a. Global positioning system (GPS) sensors or stand-alone navigation equipment, including those incorporating aircraft-based augmentation system (ABAS), satellite-based augmentation system (SBAS), or ground-based augmentation system (GBAS).
Note: For standardization within this document, the acronyms GPS/SBAS and GPS/GBAS are used to indicate SBAS augmenting GPS and GBAS augmenting GPS respectively.
b. Area navigation (RNAV) integrating data from multiple navigation sensors such as global navigation satellite system (GNSS), inertial reference units (IRU), and distance measuring equipment (DME).
c. RNAV intended for required navigation performance (RNP) operations, including advanced functions and RNP authorization required (AR).
Note: RNP AR was previously named RNP special aircraft and aircrew authorization required (SAAAR). The name was changed to RNP AR for international harmonization, but might not yet be standardized throughout all documents.
d. Barometric vertical navigation (baro-VNAV) equipment.
e. Appendix 8 provides preliminary information for manufacturers that wish to add new satellite constellations or additional frequencies to their GNSS capability. This AC will be updated as new documentation is developed for multi-constellation equipment.
f. This AC supersedes the airworthiness considerations contained in all revisions of AC 90-101, Approval Guidance for RNP Procedures with AR, and AC 90-105, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System.
Equipment previously approved per the airworthiness guidance in the 90-series ACs is still valid for the operations and conditions stated in their approvals. This AC does not replace the operational guidance found in the RNP 90-series ACs, but does replace the airworthiness guidance in the 90-series ACs. Also, this AC replaces the ACs listed in paragraph 1-3 by incorporating and updating the information they contained.