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
troubleshooting, cleaning, maintenance procedures for the MEL relief and software loading/configuration control. Special consideration should be taken to consider the maintenance of databases used for SVGS operations and the impact of installed databases that have expired. The FAA will evaluate alternative methods consistent with the FAA’s safety continuum.
4.3 ASA-SVS General Criteria and Performance Standards.
4.3.1 RTCA DO-371 section 2 provides general standards for ASA-SVS. RTCA DO-371 Section 3 provides minimum performance standards.
4.3.2 In addition to meeting the criteria of RTCA DO-371, the ASA-SVS should also meet all the criteria for a SVS found in section 4.1 of this AC.
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CHAPTER 5. PERFORMANCE EVALUATION
5.1 SVS Performance Evaluation
5.1.1 Performance demonstration. Establishing aircraft system compliance with applicable FAA regulations typically includes bench testing, simulation flight testing, data collection, and data reduction to show that the proposed performance criteria can be met. Minimum performance standards necessitate an evaluation of the system used during anticipated operational scenarios. The performance evaluations should therefore include demonstrations of taxi, take-off, missed approaches, failure conditions, cross wind conditions, and approaches into specific airports as appropriate for the system’s intended function.
5.1.2 This AC does not prescribe specific test procedures. The FAA recognizes that alternative methods can be used. Your test procedures must show compliance with the applicable regulations. System performance tests as they relate to operational capability are the most important tests. Subsystem tests are used to test subsystems during system buildup to ensure appropriate subsystem performance as it relates to overall system performance.
5.1.3 The applicant should use any of these four general verification methods as appropriate (refer to AC 25.1329-1C, AC 23.1309-1E, AC 27-1B, or AC 29-2C, as applicable):
5.1.3.1 Analysis. Demonstrate compliance using an engineering analysis.
5.1.3.2 Flight Test. Demonstrate compliance using an aircraft that is fully representative for the purpose of the test in terms of flight deck geometry, instrumentation, alerts, indications, and controls (in the air or on the ground).
5.1.3.3 Laboratory Test. Demonstrate compliance using an engineering bench representative of the final SVS/SVGS/ASA-SVS system being certified.
5.1.3.4 Simulation. Demonstrate compliance using a flight simulator.
5.1.4 The applicant should specify the individual verification methods in the certification plan. Confirm the appropriate certification office agrees with your plan before you begin. For extensions, features, and design decisions not explicitly specified in this AC, conduct human factors evaluations. Conduct these evaluations through analyses, bench, simulation, and/or flight testing, as appropriate.
5.1.5 The applicant should verify both the installed system and the individual system components meet the SVS criteria described in Chapter 4.
5.1.6 The applicant should demonstrate the system meets the performance criteria specified in Chapter 4 by flight test and other appropriate means, which can include use of a flight simulator. The flight test program assumes that the guidance system utilized to 5-1
satisfactorily position the aircraft has been separately tested and shown to fully perform its intended function. Testing and data collection to demonstrate this is not part of this document.
5.1.7 Airframe and equipment manufacturer based tests or analyses, as applicable, should be developed and conducted to validate the detailed system criteria. No specific test procedures are cited because alternative methods can be used. You can use alternate procedures if you can demonstrate that they provide all the required information.
System performance tests as they relate to operational capability are the most important tests. Subsystem tests are added during system buildup to ensure appropriate subsystem performance as it relates to overall system performance.
5.1.8 The applicant should conduct an evaluation of the system used during anticipated operational scenarios.
5.2 SVGS Performance Evaluation
5.2.1 RTCA DO-359 section 4 provides system performance verification criteria.
5.2.2 In addition to the test conditions listed in DO-359 section 4.2.2, the applicant should also demonstrate their system in representative day and night VMC.
5.2.3 Where appropriate for the performance demonstration, the non-visual conditions can be achieved either by natural obscuration or by use of a visibility limiting device in front of the pilot.
5.2.4 The use of a simulator can be considered, provided the simulator was assessed to adequately conform with respect to the aircraft and the SVGS performance, and was assessed to be suitable for the required task.
5.2.5 The workload associated with using the SVGS to fly instrument approaches to a missed approach point of 150 feet HAT should be considered when showing compliance with 14 CFR 23.2610, 25.1523, 27.1523, 29.1523, and meeting the provisions of AC
23.1523, AC 25.1523, AC 27-1B, AC 29-2C as applicable to the aircraft in which the SVGS is being installed. The FAA will evaluate alternative methods consistent with the FAA’s safety continuum.
5.3 ASA-SVS Performance Evaluation RTCA DO-371 section 4 provides system performance verification criteria.
5.4 Preventive Maintenance.
Incorporate all appropriate maintenance requirements into the Instructions for Continued Airworthiness pursuant to 14 CFR 23.1529, 25.1529, 27.1529, or 29.1529, as applicable. The FAA will evaluate alternative methods consistent with the FAA’s safety continuum.
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5.5 Environmental Testing.
Follow the guidance in AC 21-16G, RTCA Document DO-160 versions D, E, F, and G, “Environmental Conditions and Test Procedures for Airborne Equipment.”
5.6 Design Assurance.
5.6.1 Sections 23.2500, 25.1309, 27.1309, and 29.1309 require applicants to design systems to ensure they perform their intended function. The applicant should use the guidance provided in the following ACs when accomplishing their system safety assessment and showing compliance with the above regulations as applicable.
x AC 20-174, Development of Civil Aircraft and Systems x AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes x AC 25.1309-1A, System Design and Analysis x AC 27-1B, Certification of Normal Category Rotorcraft x AC 29-2C, Certification of Transport Category Rotorcraft
5.6.2 Follow the guidance in AC 20-115D, Airborne Software Development Assurance Using EUROCAE ED-12() and RTCA DO-178() to develop software. The version should be current at time of application.
Follow the guidance in AC 20-152, RTCA, Inc., Document RTCA/DO-254, Design Assurance Guidance for Airborne Electronic Hardware, to develop your airborne electronic hardware, if applicable. The version should be current at time of application.
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____________________ Appendix A APPENDIX A. SAMPLE AIRPLANE FLIGHT MANUAL (AFM) SUPPLEMENT Note: Appendix A presents a sample for the AFM supplement for STC installations. This example may not be entirely applicable to airplane manufacturers when SVS, SVGS, or ASA- SVS are approved with the type certificate. The ACO will assist the applicant in developing an appropriate Rotorcraft Flight Manual Supplement (RFMS).
Installation Center/Repair Station Model XXX SVS/SVGS/ASA-SVS 123 Fourth Street Vision System Anytown, USA
FAA-APPROVED AIRPLANE FLIGHT MANUAL SUPPLEMENT
ABC MODEL XXX YYY VISION SYSTEM AIRPLANE MAKE:
AIRPLANE MODEL:
AIRPLANE SERIAL NO.:
REGISTRATION NO.:
This document must be carried in the airplane at all times. It describes the operating procedures for the ABC Model XXX YYY vision system when it has been installed in accordance with <manufacturer's installation manual number and date>.
For airplanes with an FAA-Approved Airplane Flight Manual, this document serves as the FAA- Approved ABC Model XXX YYY Flight Manual Supplement. For airplanes that do not have an approved flight manual, this document serves as the FAA-Approved ABC Model XXX YYY Supplemental Flight Manual.
The information contained herein supplements or supersedes the basic Airplane Flight Manual dated <insert date> only in those areas listed herein. For limitations, procedures, and performance information not contained in this document, consult the basic Airplane Flight Manual.
FAA APPROVED Title Office Federal Aviation Administration City, State A-1