AdvisoryU.S. Department of Transportation Federal Aviation CircularAdministration Subject: Airworthiness Approval of Synthetic Date: 01/27/2021 AC No: 20-185A Vision Systems, Synthetic Vision Guidance Initiated by: AIR-600 S ystems and Aircraft State Awareness Synthetic Vision Systems This advisory circular (AC) provides guidance for gaining airworthiness approval for synthetic vision technology in aircraft. Specifically, when followed in its entirety, it provides an acceptable means for complying with the airworthiness regulations contained in Title 14 of the Code of Federal Regulations (14 CFR) Parts 23, 25, 27, and 29 when installing a synthetic vision system (SVS), synthetic vision guidance system (SVGS), or aircraft state awareness synthetic vision system (ASA-SVS) in airplanes and rotorcraft. As vision system technology advances, applicants are encouraged to propose alternative methods to their Aircraft Certification Office (ACO) to integrate new and novel safety enhancing vision system functions into their aircraft. The FAA will evaluate alternative methods consistent with the FAA’s safety continuum.
If you have suggestions for improving this AC, you may use the Advisory Circular Feedback form at the end of this AC.
MICHAEL C Digitally signed by MICHAEL C
ROMANOWSKI Date: 2021.01.27 21:41:34 -05'00' ROMANOWSKI Dr. Michael C. Romanowski Aviation Safety Director, Policy and Innovation Division Aircraft Certification Service
Table of Contents Paragraph Page
Chapter 1. Introduction1-1
1.1 Purpose1-1
1.2 Applicability1-1
1.3 How to Use This Document1-2
1.4 Definitions and acronyms1-2
1.5 Cancellation1-2
Chapter 2. Vision Systems Overview2-1
2.1 Synthetic Vision Systems2-1
2.2 Synthetic Vision Guidance System2-2
2.3 Aircraft State Awareness Synthetic Vision System (ASA-SVS)2-3
Chapter 3. Airworthiness Package Contents3-1
3.1 Airworthiness Package3-1
Chapter 4. System Criteria4-1
4.1 SVS General Criteria and Performance Standards4-1
4.2 SVGS General Criteria and Performance Standards4-3
4.3 ASA-SVS General Criteria and Performance Standards4-4
Chapter 5. Performance Evaluation5-1
5.1 SVS Performance Evaluation5-1
5.2 SVGS Performance Evaluation5-2
5.3 ASA-SVS Performance Evaluation5-2
5.4 Preventive Maintenance5-2
5.5 Environmental Testing5-3
5.6 Design Assurance5-3
Appendix A. Sample Airplane Flight Manual (AFM) SupplementA-1
Appendix B. Synthetic Vision System Installed in RotorcraftB-1
B.1 GeneralB-1
B.2 ApplicabilityB-1
B.3 Airworthiness ApprovalB-1
B.4 Design ConsiderationsB-1
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Appendix C. Additional Considerations for Synthetic Vision System Used for Situation
Awareness OnlyC-1
C.1 Terrain AlertingC-1
C.2 Moving Map Display that Corresponds to and Complements Synthetic Vision PFD
DisplayC-1
C.3 Minimums Audio Callout CapabilityC-2
C.4 Digital Evaluation Model (DEM) ResolutionC-2
C.5 Aircraft Flight Manual Supplement (AFMS)C-3
C.6 SVS Unusual Attitude RecoveryC-3
Appendix D. Definitions and AcronymsD-1
D.1 DefinitionsD-1
D.2 AcronymsD-4
Appendix E. Related PublicationsE-1
E.1 Related PublicationsE-1
E.2 How to Get PublicationsE-3
Appendix F. Advisory Circular Feedback InformationF-1
List of Figures Figure Page Figure 1. Synthetic Vision Diagram 2-2 iii
CHAPTER 1. INTRODUCTION
1.1 Purpose
1.1.1 The Federal Aviation Administration (FAA) has consolidated all synthetic vision related guidance into this advisory circular (AC). This revised AC provides guidance on airworthiness approvals of synthetic vision systems (SVS) previously found in AC 20- 167A. Additionally, this revised AC adds new guidance material for aircraft state awareness synthetic vision systems (ASA-SVS).
1.1.2 This AC complements existing guidance for flight guidance symbology, head-up displays (HUD), HUD equivalents, and visual display characteristics. For example, AC 25-11B, Electronic Flight Deck Displays, AC 25.1329-1C Change 1, Approval of Flight Guidance Systems and AC 23.1311-1C, Installation of Electronic Display in Part 23 Airplanes. For a complete listing of related regulations and guidance, refer to appendix E.
1.1.3 This AC is not mandatory and does not constitute a regulation. This AC describes an acceptable means, but not the only means, to install and obtain airworthiness approval for synthetic vision technologies. Applicants may propose alternate means. The contents of this document do not have the force and effect of law and are not meant to bind the public in any way. This document is intended only to provide clarity to the public regarding existing requirements under the law or agency policies.
1.1.4 The SVS guidance in this document was originally created for Part 23 aircraft and documented in AC 23-26, Synthetic Vision and Pathway Depictions on the Primary Flight Display. The original version of AC 20-167 captured the guidance contained in AC 23-26 and expanded the guidance to 14 CFR Part 25, 27, and 29 aircraft. The SVGS and ASA-SVS guidance was developed primarily for Part 25 aircraft, however you may use the guidance for Part 23, 27, and 29 aircraft. As vision system technology advances, applicants are encouraged to propose alternative methods to their ACO to integrate new and novel safety enhancing vision system functions into their aircraft. The FAA will evaluate alternative methods consistent with the safety continuum.
1.2 Applicability
1.2.1 Applicants for a type certificate (TC), amended type certificate (ATC), or supplemental type certificate (STC) may use the guidance in this AC to install SVS, SVGS, or ASA- SVS and associated equipment.
1.2.2 This AC is for airplane and rotorcraft manufacturers, modifiers, and type certification engineers seeking certification or installation guidance for their visual display system.
Sections 23.2600(a), 25.773, 27.773 and 29.773 also address vision systems using a transparent display surface located in the pilot’s outside view, such as a head-updisplay, head-mounted display, or other equivalent display. The FAA will evaluate alternative methods consistent with the FAA’s safety continuum. Such “vision systems” 1-1
could include any SVS, SVGS or ASA-SVS when implemented on HUD or HUD equivalent display.
1.2.3 This AC does not address operational aspects of SVS, SVGS or ASA-SVS or any changes in aircraft operational capability that may result from their installation.
1.3 How to Use This Document
1.3.1 This AC is based on the technical standards referenced in RTCA DO-315A, Minimum Aviation System Performance Standards (MASPS) for Enhanced Vision Systems, Synthetic Vision Systems, Combined Vision Systems and Enhanced Flight Vision Systems; RTCA DO-359, Minimum Aviation System Performance Standards (MASPS) for Synthetic Vision Guidance Systems; and RTCA DO-371, Minimum Aviation System Performance Standards (MASPS) for Aircraft State Awareness Synthetic Vision Systems. RTCA DO-315A, RTCA DO-359, and RTCA DO-371 are copyrighted by RTCA, Inc. and used with permission. Purchase information is in appendix E.
1.3.2 RTCA DO-315B is the current version of the DO-315. However, when DO-315A was revised to DO-315B, RTCA Special Committee (SC)-213 added technical standards to the earlier version of the document for the use of SVS on instrument approaches with lower than standard minima. These additional standards, however, have been superseded by standards later published in RTCA DO-359, which contains the accepted technical standards for SVGS. To preclude reference to the superseded standards in DO-315B, the FAA will reference the earlier version of DO-315 within this AC. Any applicant attempting to certify an SVGS should reference RTCA DO-359 and not RTCA DO-315B.
1.3.3 When using FAA documents referenced in RTCA DO-315A, DO-359, and DO-371, the applicant should use the most current version of the FAA document cited.
1.3.4 This material does not alter regulatory requirements.
1.3.5 This AC describes system performance.
1.3.6 Appendix A outlines a sample flight manual supplement.
1.3.7 Appendix B addresses specific installation guidance for SVS on rotorcraft. Appendix C addresses additional Part 23 considerations for situational awareness only.
1.4 Definitions and acronyms Definitions and acronyms are in appendix D.
1.5 Cancellation AC 20-185, Airworthiness Approval of Synthetic Vision Guidance System, dated December 17, 2015 is canceled.
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CHAPTER 2. VISION SYSTEMS OVERVIEW
2.1 Synthetic Vision Systems
2.1.1 Pursuant to 14 CFR 1.1, Synthetic Vision means a computer-generated image of the external scene topography from the perspective of the flight deck that is derived from aircraft attitude, high-precision navigation solution, and database of terrain, obstacles and relevant cultural features. Synthetic Vision Systems are an electronic means to display a synthetic vision image of the external scene topography to the flight crew.
Synthetic vision’s key features can also be applied to synthetic vision guidance systems, which enable instrument approaches with lower decision altitudes, and aircraft state awareness synthetic vision systems, which improve the pilot’s awareness of the aircraft’s attitude and energy state.
2.1.2 SVS provides only a supplemental view of the external scene to provide the crew with awareness of terrain, obstacles, and relevant cultural features such as runways and airport environments. SVS cannot be used in lieu of natural vision. In most cases, the display of synthetic vision is through a primary flight display from the perspective of the flight deck (egocentric), or through a secondary flight display from the perspective correlating to outside the aircraft (exocentric, like a North Up Plan view of a moving map display). This AC addresses both perspectives. The elements of a typical installed SVS are listed below, with the generic SVS system diagram shown in Figure 1.
x Display (includes interface and installation).
x System interface.
x Database of terrain and obstacles.
x Sources providing the aircraft altitude, attitude, and position.
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Figure 1. Synthetic Vision Diagram (Dashed lines represent individual system boundaries. External scene visible image is not affected by SVS.)
2.1.3 RTCA DO-315A Section 1.2 provides a SVS overview, system description, and basic system architecture.
2.2 Synthetic Vision Guidance System
2.2.1 RTCA DO-359 describes SVGS as a combination of SVS and flight guidance displayed on the primary flight display (PFD), and high precision position assurance monitors.
The SVGS flight instrument display provides a continuous, geo-spatially correct depiction of the external scene topography, including obstacles, augmented by the display of the runway of intended landing. The SVGS display is implemented on a head-down or head up PFD, designed to the guidance provided by AC 25-11B. SVGS goes beyond SVS by including additional symbology elements, integrity and performance monitors, and annunciations.
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2.2.2 RTCA DO-359 Section 1.2 provides a SVGS overview, system description, and basic system architecture.
2.2.3 This AC provides guidance on achieving airworthiness approval for a SVGS capable of supporting operations to 150 ft Height Above Touchdown (HAT) on an Instrument Landing System (ILS) instrument approach procedure. Operators must obtain separate operational approvals from Flight Standards. Reference AC 120-118, Criteria for Approval/Authorization of All Weather Operations (AWO) for Takeoff, Landing, and Rollout, for guidance on obtaining an operational approval for SA CAT I ILS instrument approaches.
2.2.4 RTCA DO-359, Minimum Aviation System Performance Standards (MASPS) for Synthetic Vision Guidance Systems, May 18, 2015, provides the minimum performance standards for SVGS. Although RTCA DO-359 provides guidance for SVGS presentation on the Head Down Display (HDD), Head Up Display (HUD), or HUD equivalent display, and cites use on ILS, LPV or GLS based instrument approach procedures, this AC only provides airworthiness guidance to applicants for eligible SVGS for ILS instrument approach procedures.
2.3 Aircraft State Awareness Synthetic Vision System (ASA-SVS)
2.3.1 RTCA DO-371 describes ASA-SVS as a combination of perspective view synthetic terrain depiction and overlaid primary flight display symbology. The ASA-SVS flight instrument provides a continuous geospatially correct depiction of the external scene topography, including obstacles, augmented by the display of the runway of intended landing. The ASA-SVS provides the pilot with a virtual day Visual Meteorological Conditions (VMC) display irrespective of the outside conditions. It is intended to support the pilots’ early recognition of non-navigation related divergence from the intended path and thereby reduce the risk of loss of control inflight (LOC-I).
2.3.2 The ASA-SVS, as described in RTCA DO-371, is intended for display full-time on the pilots’ full color head down Primary Flight Displays (PFD). RTCA DO-371 also provides guidance for implementing an ASA-SVS on a HUD, or HUD equivalent display, to supplement the head down PFD ASA-SVS presentation. The DO-371 standards are not sufficient to replace the heads down PFD ASA-SVS with a HUD ASA-SVS. If the applicant intends to use a HUD ASA-SVS without a corresponding PFD ASA-SVS they should provide additional analysis showing the HUD, or HUD equivalent display implementation meets the ASA-SVS function.
2.3.3 RTCA DO-371 Section 1.2 provides an ASA-SVS overview, system description, and basic system architecture.
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CHAPTER 3. AIRWORTHINESS PACKAGE CONTENTS
3.1 Airworthiness Package This AC specifically addresses SVS with attitude displayed on the primary flight display (PFD), SVS with a head down display other than a PFD (such as a navigation display or multifunction display), SVGS, and ASA-SVS. The applicant is responsible for the following contents in the TC, ATC or STC package (for the purpose of this AC).
3.1.1 Intended function: RTCA DO-315A, DO-359 and DO-371 provide samples of statements of intended function for SVS, SVGS and ASA-SVS respectively. The sample statements of intended function in the RTCA documents are not an exhaustive list. The applicant should do their own analysis and ensure that any statements of intended function accurately reflect the SVS, SVGS or ASA-SVS application for airworthiness approval.
3.1.2 General operation: Chapter 4 of this document provides information on general operations and specific performance criteria for the SVS.
3.1.2.1 RTCA DO-315A section 2 provides SVS general system performance standards. RTCA DO-315A section 3 provides SVS detailed system standards.
3.1.2.2 RTCA DO-359 section 2 provides SVGS general standards. RTCA DO- 359 section 3 provides SVGS standard performance standards.
3.1.2.3 RTCA DO-371 section 2 provides ASA-SVS general standards. RTCA DO-371 section 3 provides ASA-SVS minimum performance standards.
3.1.3 Performance Standards and Evaluation Criteria: The airworthiness package should include the performance criteria and an evaluation plan for the respective system. SVS performance evaluation is addressed in Chapter 5 of this document. SVGS and ASA- SVS performance evaluation is addressed in section 4 of RTCA DO-359 for SVGS and section 4 of RTCA DO-371 for ASA-SVS.
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CHAPTER 4. SYSTEM CRITERIA
4.1 SVS General Criteria and Performance Standards.
4.1.1 The proposed SVS should meet the SVS performance standards found in RTCA DO- 315A and the additional SVS criteria in section 4.1.2. Use of RTCA DO-315A and AC 20-185A provides an acceptable performance baseline for SVS. The applicant may propose alternative standards for the SVS.
4.1.2 Following are additional notes to section 2 and 3 of RTCA DO-315A.
4.1.2.1 FAA documents referenced in DO-315A have been revised since the publication of DO-315A. The applicant should refer to the most recent version of the FAA documents referenced in DO-315A.
4.1.2.2 RTCA DO-315A discusses the implementation of SVS on Class 3 Electronic Flight Bags (EFB). The FAA no longer uses the Class 3 EFB definition. If incorporating SVS on an EFB, the applicant should follow the guidance in AC 120-76D, Authorization for the Use of Electronic Flight Bags.
4.1.2.3 Multiple vision system displays. If multiple displays show EVS, SVS, CVS information, or a combination (EVS on one and SVS on another), the orientation of the displays should be the same. If the alignment of the displays is not the same, the applicant should show that the non-alignment between the displays does not mislead the flight crew or cause confusion.
4.1.2.4 SVS on HUD or HUD equivalent display.
4.1.2.4.1 The SVS display must not distort the pilot compartment view, provide a distorted (i.e., non-conformal) view of the external scene, or interfere with the pilot’s ability to safely perform any maneuvers within the operating limitations of the aircraft, including taxiing, takeoff, approach, and landing.
4.1.2.4.2 Providing complete guidance for SVS is complicated by many design variables available to manufacturers. Since synthetic vision displays can share many of the characteristics with a HUD or HUD equivalent display, applicants should use HUD, or HUD equivalent display guidance where appropriate.
4.1.2.5 SVS on a PFD.
4.1.2.5.1 Including a flight path vector or velocity vector to show the pilot the aircraft’s trajectory relative to displayed terrain is recommended.
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4.1.2.5.2 Pursuant to §§ 23.2600, 23.2600(a), 25/27/29.771, and 25/27/29.773, pilot tasks must not be degraded by the displayed imagery. Depending on the intended function of the display information, the imagery must not provide the pilot with misleading information regarding detection, accurate identification, and avoidance of terrain, obstacles, and other flight hazards.
The FAA will evaluate alternative methods consistent with the FAA’s safety continuum.
4.1.2.6 Terrain and Obstacle Database.
4.1.2.6.1 Terrain and obstacle database processing. The FAA recommends applicants use the guidance in AC 20-153B, Acceptance of Aeronautical Data Processes and Associated Databases, for terrain and obstacle databases, as well as any other databases used to create the SVS image.
Applicants may propose other solutions.
4.1.2.6.2 RTCA DO-315A provides details on terrain databases resolution and accuracy. RTCA and the FAA have updated several of the TAWS standards since the publication of DO-315A. RTCA has published DO- 367, Minimum Operational Performance Standards for Terrain Awareness and Warning System Airborne Equipment, and the FAA has published TSO-C151d. We encourage applicants to use these updated standards.
4.1.2.7 Display of Terrain and Obstacles.
4.1.2.7.1 If the intended function is “terrain awareness,” the applicant should ensure the displayed terrain is consistent with the actual terrain. The display should provide a representation of the terrain in a manner that does not misrepresent the threat posed by the terrain, even if the displayed terrain does not match the actual terrain perfectly.
4.1.2.7.2 The display should adequately portray terrain awareness, even when the display is resolution or field-of-view limited. The pilot should be aware of less than 1:1 ratio of depiction. The pilot could be made aware of this ratio by training, the Airplane Flight Manual, symbology, or other means.
Display suitability must be matched to the intended function.
4.1.2.7.3 The terrain depiction should include large bodies of water such as those depicted on Sectional Aeronautical Charts or Terminal Area Charts.
4.1.2.7.4 Runway Depiction. Runway elevations should be accurate at the approach ends and not just at the airport center.
4.1.2.7.5 Display of Obstacles. Obstacles displayed should be those deemed hazardous to the flight (or phase of flight). The applicant should provide procedures in the Instructions for Continued Airworthiness to ensure the most current obstacle database is installed. It is difficult to apply one 4-2
altitude value across a wide range of aircraft performance, from rotary wing to high performance fixed wing aircraft below which an obstacle would no longer be deemed hazardous. Generally, above 5,000 foot AGL, most obstacles are not tall enough to be hazardous. However, in the terminal area, even obstacles less than 1,000 foot AGL can be hazardous.
4.1.2.8 Features. If the SVS provides flight path guidance features, the features should complement (or correspond with) approved navigation system guidance.
4.2 SVGS General Criteria and Performance Standards.
4.2.1 SVGS should meet the performance standards in RTCA DO-359. The SVGS should also meet the SVS criteria in section 4.1 of this AC. Use of RTCA DO-359 and AC 20- 185A together provides an acceptable performance baseline for the SVGS.
4.2.2 Additional Notes to section 2 and 3 of RTCA DO-359.
4.2.2.1 AC 120-118 provides guidance on receiving operational approval to use an SVGS to conduct an SA CAT I ILS instrument approach.
4.2.2.2 If the applicant implements SVGS only on a HDD, the aircraft should be capable of displaying the SVGS simultaneously on both the pilot and copilot’s PFD.
4.2.2.3 The terrain, runway and obstacle database standards for the SVGS specified in RTCA DO-359, section 2.5 should support intended function, and the processes for their production and update should meet the standards in RTCA DO-200B, Standards for Processing Aeronautical Data, dated June 18, 2015. Navigation databases supporting creation of the SVS image should meet the standards in RTCA DO-201A, Standards for Aeronautical Information, dated April 19, 2000, or subsequent revisions. Terrain and obstacle databases supporting creation of the SVS image should use RTCA DO-276C, User Requirements for Terrain and Obstacle Data, dated September 22, 2015, section 4 to define data quality requirements (DQRs) adequate to support intended function. Airport map databases supporting the creation of the SVS image should meet the standards in RTCA DO-272D, User requirements for Aerodrome Mapping Information, dated September 22, 2015 or subsequent revisions.
4.2.2.4 Continued Airworthiness and Maintenance. Pursuant to 14 CFR 23.1529,
25.1529, 27.1529 and 29.1529, the applicant must develop instructions for continued airworthiness for maintaining the SVGS and its components.
Other maintenance tasks may be developed as a result of the safety assessment, design reviews, manufacturer’s recommendations and Maintenance Steering Group 3 (MSG-3) analyses that are conducted.
These instructions include, but are not limited to removal and replacement, 4-3