U.S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Airworthiness Approval of Enhanced Vision System, Enhanced Flight Vision System, and Combined Vision System Equipment Date: AC No: 20-167B Initiated by:
AIR-626B This advisory circular (AC) provides guidance for gaining airworthiness approval for enhanced vision systems in aircraft. Specifically, it provides one acceptable means for complying with title 14, Code of Federal Regulations (14 CFR) part 23, 25, 27, or 29 airworthiness regulations when installing an enhanced vision system (EVS), an enhanced flight vision system (EFVS) or combined vision system (CVS) in an aircraft. This guidance was developed primarily for part 25 aircraft. You may also use this guidance for part 23, 27, and 29 aircraft. As vision system technology advances, applicants are encouraged to propose alternative methods to their AIR certification branch to integrate new and novel safety enhancing vision system functions into their aircraft.
If you have suggestions for improving this AC, you may use the Advisory Circular Feedback Form at the end of this AC.
Daniel J. Elgas Aviation Safety Director, Policy and Standards Division, Aircraft Certification Service
AC 20-167B
TABLE OF CONTENTS Paragraph Page
CHAPTER 1. INTRODUCTION1-1
1.1 Purpose1-1
1.2 Applicability1-1
1.3 Cancellation1-2
1.4 Related Material1-2
1.5 Definition of Key Terms1-2
1.6 Background1-2
CHAPTER 2. VISION SYSTEMS OVERVIEW2-1
2.1 Enhanced Vision Systems (EVS)2-1
2.2 Enhanced Flight Vision Systems (EFVS)2-3
2.3 Combined Vision Systems (CVS)2-6
CHAPTER 3. AIRWORTHINESS PACKAGE CONTENTS3-1
3.1 Airworthiness Package3-1
3.2 Intended Function3-1
3.3 Certification of a pre- 14 CFR 91.176 EFVS as an EFVS Landing System3-2
CHAPTER 4. SYSTEM CRITERIA4-1
4.1 EVS (or CVS when EVS and SVS combined) – General Criteria4-1
4.2 EVS Specific Criteria4-5
4.3 CVS Specific Criteria4-7
4.4 EFVS – General and Specific Criteria4-8
CHAPTER 5. SYSTEMS INSTALLATION CONSIDERATIONS5-1
5.1 EVS/EFVS/CVS Installations Considerations5-1
5.2 Continued Airworthiness and Maintenance5-2
5.3 EFVS Environmental Specifications5-2
5.4 HIRF Considerations for All Installations (EVS, CVS, and EFVS)5-2
5.5 Software and Hardware Design Assurance5-3
5.6 EVS/EFVS/CVS System Safety Design Criteria5-3
5.7 EVS/EFVS/CVS Required Safety Level5-3
CHAPTER 6. PERFORMANCE EVALUATION6-1
6.1 EVS/EFVS Performance Demonstration6-1
6.2 Performance Demonstration of EFVS Landing System6-2
APPENDIX A. FAA EFVS 14 CFR COMPLIANCE (PARTIAL LIST)A-1
APPENDIX B. SAMPLE EFVS FLIGHT TEST CONSIDERATIONSB-1
APPENDIX C. DETERMINING QUANTIFIED VISUAL ADVANTAGEC-1
APPENDIX D. SAMPLE AIRPLANE FLIGHT MANUAL (AFM) SUPPLEMENTD-1
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AC 20-167B TA
BLE OF CONTENTS Paragraph Page APPENDIX E. INSTALLATION OF ENHANCED VISION SYSTEM ON
ROTORCRAFTE-1
APPENDIX F. DEFINITIONS AND ACRONYMSF-1
APPENDIX G. RELATED MATERIALG-1
FIGURES Number Page
Figure 2-1. Enhanced Vision Diagram2-2
Figure 4-1. Minimum Detection Range4-12
Figure B- 1. Depiction of Visual AdvantageB-2
TABLES Number Page
Table 1-1. Title 14 CFR 91.176 EFVS Visibility and Visual Reference Requirements4-11
Table 2-1. System Operating Phases for Considerations5-4
Table A-1. EFVS Acceptable Methods of ComplianceA-1
Table B.1. EFVS Flight Test Evaluation MatrixB-10
Table B.2. EFVS Landing System Supplemental Flight Test Evaluation MatrixB-12
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AC 20-167B CHAPTER 1. I NTRODUCTION
1.1 Purpose.
In this advisory circular (AC), the Federal Aviation Administration (FAA) provides guidance on airworthiness approvals of enhanced vision system (EVS), combined vision system (CVS), and enhanced flight vision system (EFVS) equipment installation.
The guidance is performance based and not limited to a specific sensor technology. This action will accommodate future growth in sensor technologies used in vision systems.
This guidance was developed primarily for title 14, Code of Federal Regulations (14 CFR) part 25 aircraft. You may also use this guidance for 14 CFR part 23, 27, and 29 aircraft.
Note: As vision system technology advances, applicants are encouraged to propose alternative methods to their AIR certification branch to integrate new and novel safety enhancing vision system functions into their aircraft.
1.1.1 Existing ACs address flight guidance symbology, head-up displays (HUD) and visual display characteristics (for example, AC 25-11B, Electronic Flight Displays, AC
25.1329-1C, 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 appendices A and G of this AC. This AC complements existing guidance.
1.2 Applicability.
1.2.1 The guidance provided in this AC is for airplane manufacturers, modifiers, foreign regulatory authorities, Federal Aviation Administration (FAA) transport airplane type certification engineers, and FAA designees.
1.2.2 This is a guidance document. Its content is not legally binding in its own right and will not be relied upon by the Department as a separate basis for affirmative enforcement action or other administrative penalty. Conformity with the guidance document is voluntary only. Nonconformity will not affect rights and obligations under existing statutes and regulations.
1.2.3 The FAA will consider other means of demonstrating compliance that an applicant may elect to present. Terms such as “should,” “may,” and “must” are used only in the sense of ensuring the applicability of this particular method of compliance when the acceptable method of compliance in this document is used. If the FAA becomes aware of circumstances in which following this AC would not comply with the applicable regulations, the FAA may require additional substantiation or design changes as a basis for finding compliance.
1.2.4 The material contained in this AC does not change or create any additional regulatory requirement, nor does it authorize changes in, or permit deviations from, existing regulatory requirements.
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AC 20-167B
1.3 Cancellation.
This AC cancels AC 20-167A, Airworthiness Approval of Enhanced Vision System, Synthetic Vision System, Combined Vision System, and Enhanced Flight Vision System Equipment, dated December 6, 2016.
1.4 Related Material.
1.4.1 This AC provides methods, procedures, and practices acceptable to the FAA for complying with applicable certification regulations. EFVS compliance references are listed in appendix A. The latest version of each AC referenced in this document is available on the FAA website at FAA Advisory Circulars and on the Dynamic Regulatory System.
1.4.2 The preamble accompanying the final rule, Revisions to Operational Requirements for the Use of Enhanced Flight Vision Systems (EFVS) and to Pilot Compartment View Requirements for Vision Systems (81 FR 90126; December 13, 2016) specifically references paragraphs 4.5.3.4, 4.5.3.4.8.4, and 6.2.6.4 of AC 20-167A. These referenced sections equate to sections 4.4.3, 4.4.3.1.8.4, and 6.2.5.4 of this AC, respectively.
1.4.3 Certain material within this AC is based upon 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-315A is copyrighted by RTCA, Inc. and used with permission. Purchase information is in appendix G.
1.5 Definition of Key Terms.
See appendix F for terms and definitions that apply to this AC.
1.6 Background.
This AC is for aircraft manufacturers, modifiers, and type certification engineers seeking certification or installation guidance for visual display systems. Sections
23.2600(a), 25.773, 27.773 and 29.773 address vision systems using a transparent display surface located in the pilot’s outside view, such as a head-up display, head mounted display, or other equivalent display. Such “vision systems” could include any EVS, EFVS, SVS, or CVS.
1.6.1 The revision of AC 20-167A is part of a restructuring of all installation guidance for EVS, EFVS, CVS and synthetic vision systems (SVS). AC 20-167B contains all installation guidance material for EVS, EFVS, and CVS. All installation guidance regarding SVS, synthetic vision guidance systems, and aircraft state awareness synthetic vision systems has been consolidated into AC 20-185A, Airworthiness Approval of Synthetic Vision Systems, Synthetic Vision Guidance Systems, and Aircraft State Awareness Synthetic Vision Systems.
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AC 20-167B Note: SVS are electronic systems used to display a computer-generated image of the applicable external topography from the perspective of the flightdeck that is derived from aircraft attitude, altitude, position, and a coordinate-referenced database. Since this AC addresses EVS, EFVS, and CVS, installation guidance material for SVS that previously existed in AC 20-167A has been relocated into AC 20-185A.
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AC 20-167B CHAPTER 2. VISION SYSTEMS OVERVIEW
2.1 Enhanced Vision Systems (EVS).
2.1.1 An EVS is an electronic means to provide a display of the forward external scene topography using imaging sensors including forward looking infrared, millimeter wave (MMW) radiometry, MMW radar, and low-light-level image intensifying. EVS does not necessarily provide the additional flight information/symbology on a head-up display (HUD) or equivalent display that is required for EFVS operations under 14 CFR
91.176. While EVS share a similarity with EFVS technology, an EVS does not have to be integrated with a flight guidance system. An EVS may provide additional awareness about the external scene to the pilot, but without the additional capabilities provided by an EFVS, it is not eligible to conduct EFVS operations under § 91.176 (a) or (b).
2.1.2 The elements of an installed EVS are listed below, with the EVS diagram shown in Figure 1:
• EVS sensor system,
• Display processor,
• EVS display,
• Pilot controls/interface, and
• Mounting.
Note 1: While an EFVS contains all the elements of an EVS, for the purposes of this AC, any discussion of an EVS excludes an EFVS.
Note 2: For the purposes of this AC, any guidance that applies to a HUD also applies to displays equivalent to a HUD.
Note 3: A head-worn display (HWD) could potentially meet the requirement for a HUD-equivalent display. The FAA does not currently have any published installation criteria specifically addressing HWDs. Applicants should propose a means of compliance that demonstrates that the proposed HWD is equivalent to a HUD.
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AC 20-167B Figure 2-1. Enhanced Vision Diagram Note: Dashed lines and shading represent individual system boundaries for EVS and EFVS.
2.1.3 EVS sensors are currently categorized as passive or active sensors.
2.1.3.1 Passive Sensors.
Scene contrast detected by passive infrared sensors can be much different than that detected by natural pilot vision. On a dark night, thermal differences of objects, while not detectable by the naked eye, will be detected depending on the capabilities of an imaging infrared system.
However, contrasting colors in visual wavelengths distinguished by the naked eye may not be visible using an imaging infrared system. Sufficient thermal scene contrast allows shapes and patterns of certain visual references to be recognized in the infrared image by the pilot. However, depending on environmental conditions, they can also appear different to a pilot in the infrared image than they would with normal vision.
2.1.3.2 Active Sensors.
Scene contrast detected by active systems depends on several parameters:
whether the transmitter is centered on the aircraft velocity vector, display updates rates, latency, range resolution, sensitivity, dynamic range, and azimuth and elevation resolution. For an active infrared thermal imaging 2-2
AC 20-167B sensor, the infrared illuminator has the potential to illuminate more weather obscurations, which can compete with scene contrast and interpretation. One advantage of millimeter wave radar systems is their general immunity to weather obscurations.
2.1.4 Unlike the pilot's external view, the enhanced vision image can be a monochrome, twodimensional display. Some, but not all, of the depth cues found in the natural view are also found in the imagery. The quality of the enhanced vision image and the level of enhanced vision sensor performance depend on atmospheric and external visible and non-visible energy source conditions. Gain settings of the sensor, and brightness or contrast settings of the display, can significantly affect image quality. Certain system characteristics could create distracting and confusing display artifacts.
2.1.5 Unlike with EFVS, an aircraft with EVS does not necessarily provide the additional flight information or symbology required by § 91.176. Unlike an EFVS, an EVS may be displayed on a head down display or on a HUD or equivalent display. The EVS display may not be able to present the image and flight symbology in the same scale and alignment as the outside view. An EVS can provide a display of the external scene topography to the pilot but does not meet the regulatory requirements of § 91.176. An EVS cannot be used as a means to enhance flight visibility or to identify the required visual references in order to gain operational credit and descend below the decision altitude/decision height (DA/DH) or minimum descent altitude (MDA).
2.2 Enhanced Flight Vision Systems (EFVS).
2.2.1 An EFVS is defined in 14 CFR 1.1 as “an installed aircraft system which uses an electronic means to provide a display of the forward external scene topography (the natural or engineered features of a place or region especially in a way to show their relative positions and elevation) through the use of imaging sensors, including but not limited to forward-looking infrared, millimeter wave radiometry, millimeter wave radar, or low-light level image intensification.” An EFVS includes the display element, sensors, computers and power supplies, indications, and controls.
2.2.2 Under § 91.176(a)(1) and § 91.176(b)(1), the EFVS must present EFVS sensor imagery, aircraft flight information, and flight symbology on a head-up display, or an equivalent display, so that the imagery, information and symbology are clearly visible to the pilot flying in their normal position with the line of vision looking forward along the flight path.
An equivalent display must be some type of head-up presentation of the required information. A head-down display does not meet the regulatory requirement. For the EFVS monitor display criteria, see sections 4.4.2 and B.10 of this AC.
2.2.3 An EFVS is intended to be used to conduct an operation in which the enhanced vision image is used in lieu of natural vision to perform an approach or landing, determine the enhanced flight visibility, identify required visual references, or conduct a rollout. An EFVS requires a real-time imaging sensor that provides enhanced visibility in low 2-3
AC 20-167B visibility conditions and a level of safety suitable for the proposed operational procedure.
2.2.4 An EFVS with airworthiness approval will be designated as an EFVS approach system or EFVS landing system as described below. Under § 91.176, airworthiness approval being sought by the applicant may require additional basic equipage. Acceptable criteria for EFVS approach systems and EFVS landing systems are discussed in section 4.4 of this AC. EFVS approach systems and EFVS landing systems are briefly described in the following sections:
2.2.4.1 EFVS Approach System.
The installed EFVS has been demonstrated to meet an acceptable criteria, such as the criteria described in this AC, for an EFVS approach system to be used to conduct EFVS operations under § 91.176(b). The system design relies on sufficient visibility conditions to mitigate a loss of EFVS function in order to enable unaided flare and rollout. Operational guidance for use of an EFVS is published in AC 90-106B, Enhanced Flight Vision Systems.
2.2.4.2 EFVS Landing System.
The installed EFVS has been demonstrated to meet an acceptable criteria, such as the criteria described in this AC, for an EFVS landing system to be used for EFVS operations conducted under § 91.176(a). The system design relies on sufficient visibility conditions to mitigate loss of EFVS function in order to enable unaided flare and rollout. An EFVS that meets the certification criteria for an EFVS landing system also meets the certification criteria for an EFVS approach system. Operational guidance for the use of an EFVS is published in AC 90-106B.
2.2.5 Under § 91.176(a)(1) and § 91.176(b)(1), the basic elements of an installed EFVS are listed below. Guidance on specific system criteria that may be acceptable for an EFVS can be found in Chapter 4 of this AC.
2.2.5.1 The EFVS must have an electronic means to provide a display of the forward external scene topography (the applicable natural or engineered features of a place or region especially in a way to show their relative positions and elevation) through the use of imaging sensors including, but not limited to forward-looking infrared, millimeter wave radiometry, millimeter wave radar, and low-light level image intensification.
2.2.5.2 The EFVS must present sensor imagery, aircraft flight information, and flight symbology on a head-up display, or an equivalent display, so that the imagery, information, and symbology are clearly visible to the pilot flying in their normal position with the line of vision looking forward along the flight path. Aircraft flight information and flight symbology must consist of at least airspeed, vertical speed, aircraft attitude, heading, altitude, command guidance (as appropriate for the approach to be flown), 2-4
AC 20-167B path deviation indications, flight path vector, and flight path angle reference cue. Additionally, for aircraft other than rotorcraft, the EFVS must display a flare prompt or flare guidance when conducting § 91.176(a) operations.
2.2.5.3 The display should meet the following criteria:
2.2.5.3.1 The EFVS must present the displayed EFVS sensor imagery, attitude symbology, flight path vector, flight path angle reference cue (FPARC), command guidance as appropriate and other cues, which are referenced to the EFVS sensor imagery and external scene topography, so that they are aligned with and scaled to the external view.
Note: The European Union Aviation Safety Agency (EASA) imposes additional symbology requirements that are not required by the FAA for certification or for operational approvals. Applicants that will be seeking EASA approval should consult the latest EASA guidance material to ensure compliance with EASA regulations.
2.2.5.3.2 The EFVS must display the FPARC with a pitch scale. The FPARC must be selectable by the pilot to the desired descent angle for the approach and be sufficient to monitor the vertical flight path of the aircraft. The descent angle may also be automatically set to a value found in an onboard database.
2.2.5.3.3 The displayed sensor imagery, aircraft flight information, and flight symbology must not adversely obscure the pilot's outside view or field of view through the flightdeck window.
2.2.5.3.4 The EFVS includes the display element, sensors, computers/power supplies, indications, and controls. It may receive inputs from an airborne navigation system or flight guidance system.
2.2.5.3.5 The EFVS must provide display characteristics, dynamics, and cues suitable for manual control of the aircraft.
2.2.5.3.6 Installations designed to be eligible for EFVS landing system operations must also present a flare prompt or flare guidance and present height above ground level (such as that provided by a radio altimeter or equivalent device). Refer to section 4.4 of this AC for guidance on acceptable performance criteria.
2.2.6 Enhanced flight vision systems.
Enhanced flight vision systems display both symbology and imagery.
2.2.6.1 Symbology luminates a small fraction of the total display area of the HUD, leaving much of that area free of symbology and imagery that could interfere with the pilot's view out the window through the display.
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AC 20-167B
2.2.6.2 The EVS image is in the center of the pilot's regulated “pilot compartment view.” In accordance with §§ 23.2600, 25.773(a), 27.773(a), and
29.773(a), the pilot compartment view must be clear, undistorted, and free of glare and reflection that could interfere with the normal duties of the minimum flightcrew. A video image can be more difficult for the pilot to see through than symbols displayed on the HUD. Unlike symbology, the video image illuminates, to some degree, most of the total display area of the HUD with much greater potential interference with the pilot compartment view. The outside scene must be visible, both through and around the display when the EVS image is displayed.
2.2.7 Unlike the pilot's external view, the enhanced flight vision image is historically a monochrome, two-dimensional display. Some, but not all the depth cues found in the natural view are also found in the imagery. The quality of the enhanced flight vision image and the level of enhanced flight vision sensor performance could depend significantly on the atmospheric and external light source conditions. Gain settings of the sensor and brightness or contrast settings of the HUD can significantly affect image quality. Certain system characteristics could create distracting and confusing display artifacts. Finally, this is a sensor-based system that is intended to provide a conformal perspective. Refer to figure 1 for a diagram of the system.
2.2.8 For the primary display, the regulations also make provision for an equivalent display.
Section 91.176(a)(1)(i)(B) states that EFVS sensor imagery, aircraft flight information, and flight symbology must be presented “on a head-up display, or an equivalent display, so that the imagery, information and symbology are clearly visible to the pilot flying in their normal position with the line of vision looking forward along the flight path.” To meet part 91 operational requirements, an equivalent display must be some type of head-up presentation of the required information. A head-down display does not meet the operational regulatory requirement. For guidance on monitoring display criteria, see section 4.4.2 of this AC.
2.3 Combined Vision Systems (CVS).
2.3.1 The CVS concept involves a combination of SVS and either EVS or EFVS. Some examples of a CVS include database-driven synthetic vision images combined with real-time sensor images superimposed and correlated on the same display. This includes selective blending of the two technologies based on the intended function of the vision system for which approval is sought. For example, on an approach, most of the arrival would utilize the SVS picture. As the aircraft nears the runway, the picture gradually and smoothly transitions from synthetic to enhanced vision, either for SVS picture validation or displaying the runway environment.
2.3.2 CVS applicants are expected to meet applicable performance criteria for each incorporated system. EVS and EFVS related guidance is located in this document. SVS related guidance can be found in AC 20-185A.
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