AC 20-167B Appendix E APPENDIX E. INSTALLATION OF ENHANCED VISION SYSTEM ON
ROTORCRAFT E.1 General.
This appendix provides guidelines for the installation of EVS installed in rotorcraft as non-required safety enhancing equipment. Policy statements PS-ASW-27, 29-10 (dated May 29, 2013), PS-AIR-21.8-1602 (dated March 31, 2016), and PS-ASW-27-15 (dated June 30, 2015) were published to promote standardized installation of non-required safety enhancing equipment. Contact the appropriate FAA office responsible for rotorcraft standards for guidance. Also refer to AC 27-1B CHG 1-9 and AC 29-2C CHG 9 for certification guidance.
E.2 Applicability.
There are unique aspects to rotorcraft that do not apply to fixed wing aircraft. Rotorcraft typically operate at altitudes much closer to obstacles and the ground than fixed-wing aircraft. Additionally, they are inherently unstable and, without a stabilization system, require hands-on control at all times, accompanied by constant visual scans to keep the pilot oriented correctly. There are advantages and disadvantages to presenting EVS information to the pilot. Particular issues of concern are the compelling nature of the display used in a VFR see-and-avoid environment, the presentation of misleading information relating to aircraft location relative to hazards (particularly in night operations), and the installation of EVS or CVS displays that interact with automated flight control systems and flight guidance systems.
E.3 Airworthiness Approval.
For rotorcraft, the FAA has determined that installation of EVS or CVS on a primary flight display, either ADI or NAV display, requires AIR certification branch involvement through the STC process, under FAA Order 8900.1A, Volume 4, Chapter 9 Selected Field Approvals Figure 4-68, Major Alterations Job Aid. Installations on a primary flight display will involve human factors evaluations and flight test evaluations.
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AC 20-167B Appendix E E.4 Design Considerations.
The FHA developed for the system should define the hazards of presenting misleading information to the pilot, and the loss of an EVS feature. The system should be designed accordingly. The hazard classification will be based on display location, intended function of the system features, and phase of flight. The hazard classification of misleading information for EVS/CVS on the primary flight displays will be higher than the classification of misleading information on a display outside the pilot’s primary field of view. For example, the hazard classification of misleading information may be lower if the EVS/CVS is placed on ancillary displays not used for the display of flight information and not in the pilot’s primary field of view. However, for rotorcraft the FAA does not accept “situation awareness only” information on primary flight displays (either PFD or MFD within the pilot’s primary field of view). Therefore, the intended function of the EVS/CVS should be defined. If helicopter terrain awareness and warning system (HTAWS) or HTAWS-like features are incorporated, see TSO-C194.
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AC 20-167B Appendix F APPENDIX F. DEFINITIONS AND ACRONYMS F.1 Definitions.
F.1.1 Appliance (14 CFR 1.1).
Any instrument, mechanism, equipment, part, apparatus, appurtenance, or accessory, including communications equipment, that is used or intended to be used in operating or controlling an aircraft in flight, is installed in or attached to the aircraft, and is not part of an airframe, engine, or propeller.
F.1.2 Approach Lighting Designators.
• ALSF-I. High Intensity Approach Lighting System with Sequenced Flashing Lights, Category I Configuration.
• ALSF-II. High Intensity Approach Lighting System with Sequenced Flashing Lights, Category II Configuration.
• MALSR. Medium Intensity Approach Lighting System with Runway Alignment Indicator Lights.
• SSALR. Simplified Short Approach Lighting System with Runway Alignment Indicator Lights.
• MALSF. Medium Intensity Approach Lighting System with Sequenced Flashing Lights.
• RAIL. Runway Alignment Indicator Lights (RAIL).
• SF. Sequenced Flashing Lights (SF).
F.1.3 Combined Vision System (CVS).
A system which combines information from an enhanced vision system and a synthetic vision system in a single integrated display.
F.1.4 Command Guidance.
Symbolic information that directs the pilot to follow a course of action to control attitude or thrust in a specific situation (for example, flight director).
F.1.5 Conformal (AC 25-11B).
Refers to displayed graphic information that is aligned and scaled with the outside view.
F.1.6 Decision Altitude (14 CFR 1.1).
A specified altitude in an instrument approach procedure at which the pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision altitude is expressed in feet above mean sea level.
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AC 20-167B Appendix F F.1.7 Decision Height (14 CFR 1.1).
A specified height above the ground in an instrument approach procedure at which the pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision height is expressed in feet above ground level.
F.1.8 Egocentric.
Used to define the view of a display image that correlates to inside the aircraft. One example is what the flightcrew would see out the window from a forward-facing perspective.
F.1.9 Enhanced Flight Visibility (EFV) (14 CFR 1.1).
The average forward horizontal distance, from the flight deck of an aircraft in flight, at which prominent topographical objects can be clearly distinguished and identified by day or night by a pilot using an EFV system.
F.1.10 Enhanced Flight Vision System (EFVS) (14 CFR 1.1).
An installed aircraft system which uses an electronic means to provide a display of the forward external scene topography (the natural or manmade 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/or low light level image intensification.
An EFVS includes the display element, sensors, computers and power supplies, indications, and controls.
F.1.11 Enhanced Vision System (EVS).
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, such as a forward looking infrared, millimeter wave radiometry, millimeter wave radar, low light level image intensifying.
F.1.11.1 Unlike an EFVS, an EVS does not necessarily provide the additional flight information/symbology required by § 91.176, might not use a HUD or an equivalent display, and might not be able to present the image and flight symbology in the same scale and alignment as the outside view. This system can provide situation awareness to the pilot but does not meet the regulatory requirements of § 91.176. As such, an EVS cannot be used as a means to determine enhanced flight visibility or to identify the required visual references and descend below DA/DH or MDA.
F.1.12 Equivalent Display.
In the context of § 91.176, a display which has at least the following characteristics:
• A head-up presentation not requiring transition of visual attention from head down to head up.
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AC 20-167B Appendix F
• Displays sensor-derived imagery conformal (as defined in SAE AS 8055A) with the pilot’s external view.
• Permits simultaneous view of the EFVS sensor imagery, required aircraft flight symbology, and the external view.
• Display characteristics and dynamics are suitable for manual control of the aircraft.
F.1.13 Exocentric.
Used to define the view of a display image that correlates to outside the aircraft. One common exocentric view would be a “North Up Plan” view shown on moving map displays.
F.1.14 Eye Reference Point.
The point in the flightdeck that allows for a finite reference enabling the precise determination of geometric entities that define the layout of the flightdeck and displays.
F.1.15 Field of Regard (FOR) (SAE ARP 5677).
The angular extent of the external world that is represented on a display.
F.1.16 Field of View (FOV).
The angular extent of the display that can be seen by either pilot with the pilot seated at the pilot’s station.
F.1.17 Flare Guidance.
Provides explicit command guidance for the pilot to flare the aircraft.
F.1.18 Flare Prompt.
The flare prompt advises the pilot when it is time to begin making the control inputs for the flare maneuver and transition to landing. A flare prompt does not provide command guidance for maneuvering the airplane with regard to the rate or magnitude of manual inputs, alignment to runway heading nor touching down at a specific point on the runway.
F.1.19 Flicker (RTCA DO-315A).
High frequency luminance variations.
F.1.20 Flight Path Angle Reference Cue.
A pilot selectable reference cue on the pitch scale displaying the desired approach angle.
F.1.21 Flight Path Vector.
A symbol on the primary display (HUD or PFD) that shows where the aircraft is actually going, the sum of all forces acting on the aircraft.
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AC 20-167B Appendix F F.1.22 Flight Visibility (14 CFR 1.1).
The average forward horizontal distance, from the flight deck of an aircraft in flight, at which prominent unlighted objects can be seen and identified by day and prominent lighted objects can be seen and identified by night.
F.1.23 Head-Up Display (HUD) (AC 25-11B).
A display system that projects primary flight information (for example, attitude, air data, guidance, etc.) on a transparent screen (combiner) in the pilot’s forward field of view, between the pilot and the windshield. This allows the pilot to simultaneously use the flight information while looking along the forward path out the windshield, without scanning the head-down displays. The flight information symbols should be presented as a virtual image focused at optical infinity. Attitude and flight path symbology needs to be conformal (that is, aligned and scaled) with the outside view.
F.1.24 IFR Conditions (14 CFR 1.1).
Weather conditions below the minimum for flight under visual flight rules.
F.1.25 Instrument (14 CFR 1.1).
A device using an internal mechanism to show visually or aurally the attitude, altitude, or operation of an aircraft or aircraft part. It includes electronic devices for automatically controlling an aircraft in flight.
F.1.26 Jitter (RTCA DO-315A).
High frequency positional oscillations.
F.1.27 Latency (AC 25-11B).
The time taken by the display system to react to a triggered event coming from an input/output device, the symbol generator, the graphic processor, or the information source.
F.1.28 Minimum Descent Altitude (14 CFR 1.1).
The lowest altitude specified in an instrument approach procedure, expressed in feet above mean sea level, to which descent is authorized on final approach or during circleto-land maneuvering until the pilot sees the required visual references for the heliport or runway of intended landing.
F.1.29 Noise Equivalent Power.
Measure of the sensitivity of an optical detector or detector system.
F.1.30 Noise Equivalent Temperature Difference (NETD).
A measure of the sensitivity of a detector of thermal radiation in the infrared, terahertz radiation, or microwave radiation parts of the electromagnetic spectrum.
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AC 20-167B Appendix F F.1.31 Non-Uniformity Correction (NUC).
Calibration of a detector utilizing more than one detector element.
F.1.32 Precision Approach Procedure (14 CFR 1.1).
A standard instrument approach procedure in which an electronic glideslope is provided, such as ILS and PAR.
F.1.33 Primary Flight Display (PFD).
The displays used to present primary flight information.
F.1.34 Rmax.
The maximum range a radar can detect.
F.1.35 Situation Information (AC 120-29A).
Information that directly informs the pilot about the status of the aircraft system operations or specific flight parameters including flight path.
F.1.36 Synthetic Vision (14 CFR 1.1).
A computer-generated image of the external scene topography from the perspective of the flightdeck that is derived from aircraft attitude, high-precision navigation solution, and database of terrain, obstacles and relevant cultural features.
F.1.37 Synthetic Vision System (SVS) (14 CFR 1.1).
An electronic means to display a synthetic vision image of the external scene topography to the flightcrew.
F.1.38 SVS Topography.
Maps or charts of natural and man-made features of a place or region especially in a way to show their relative positions and elevations, as applicable whenever deemed appropriate and practicable.
F.1.39 Thermal Crossover.
The natural phenomenon that normally occurs twice daily when temperature conditions are such that there is a loss of contrast between two adjacent objects on infrared imagery.
F.1.40 Threshold Crossing Height (TCH) (Pilot/Controller Glossary).
The theoretical height above the runway threshold at which the aircraft’s glideslope antenna would be if the aircraft maintains the trajectory established by the mean ILS glideslope.
F.1.41 V1 (AC 120-62).
The speed selected for each takeoff, based upon approved performance data and specified conditions, which represents:
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AC 20-167B Appendix F
5. The maximum speed by which a rejected takeoff must be initiated to assure that a safe stop can be completed within the remaining runway, or runway and stopway;
6. The minimum speed which assures that a takeoff can be safely completed within the remaining runway, or runway and clearway after failure of the most critical engine at a designated speed; and
7. The single speed which permits a successful stop or continued takeoff when operating at the minimum allowable field length for a particular weight.
F.1.42 Vr (AC 120-62).
Rotation speed.
F.1.43 Visual References.
Visual information the pilot derives from the observation of real-world cues, out the flightdeck window, used as a primary reference for aircraft control or flight path assessment.
F.2 Acronyms AC Advisory Circular AFM Airplane Flight Manual BIT Built in Test CVS Combined Vision System DA Decision Altitude DH Decision Height EASA European Union Aviation Safety Agency EFVS Enhanced Flight Vision System EVS Enhanced Vision S ystem FAA Federal Aviation Administration FHA Functional Hazard Assessment FMEA Failure Mode and Effects Analysis FOR Field of Regard FOV Field of View FTA Fault Tree Analysis HAT Height Above Touchdown HDD Head-Down Display HMI Hazardously Misleading Information HTAWS Helicopter Terrain Awareness and Warning System HUD Head-Up Display IFR Instrument Flight Rules ILS Instrument Landing System MDA Minimum Descent Altitude F-6
AC 20-167B Appendix F MFD Multi-Function Display MRAD M illiradian ND Navigation display NETD Noise Equivalent Temperature Difference NUC Non-uniformity Correction PFD Primary Flight Display PIO Pilot Induced Oscillation PSCP Project Specific Certification Plan RFM Rotorcraft Flight Manual RVR Runway Visual Range SSA System Safety Assessment STC Supplemental Type C ertificate SVS Synthetic Vision S ystem TAWS Terrain Awareness and Warning System TC Type Certificate TCH Threshold Crossing H eight TDZE Touchdown Zone E levation F-7
AC 20-167B Appendix G APPENDIX G. R ELATED MATERIAL G.1 Title 14, Code of Federal Regulations.
The following 14 CFR regulations are related to this AC. You can download the full text of these regulations from the Federal Register website at www.ecfr.gov.
• Part 1, Definitions and Abbreviations.
• Part 23, Airworthiness Standards: Normal Category Airplanes.
• Part 25, Airworthiness Standards: Transport Category Airplanes.
• Part 27, Airworthiness Standards: Normal Category Rotorcraft.
• Part 29, Airworthiness Standards: Transport Category Rotorcraft.
• Part 91, General Operating and Flight Rules.
G.2 FAA Advisory Circular(s).
The following publications are related to the guidance in this AC. You should refer to the latest version for guidance, which is available on the Dynamic Regulatory System (DRS) website at drs.faa.gov/browse.
• AC 20-185A, Airworthiness Approval of Synthetic Vision Systems, Synthetic Vision Guidance Systems, and Aircraft State Awareness Synthetic Vision Systems.
• AC 21-16G, RTCA Document DO-160 versions D, E, F,G “Environmental Conditions and Test Procedures for Airborne Equipment.”
• AC 23-18, Installation of Terrain Awareness and Warning System (TAWS) Approved for Part 23 Airplanes.
• AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes.
• AC 23.1311-1C, Installation of Electronic Display in Part 23 Airplanes.
• AC 25-11B, Electronic Flight Displays.
• AC 25-23, Airworthiness Criteria for the Installation Approval of a Terrain Awareness and Warning System (TAWS) for Part 25 Airplanes.
• AC 25.571-1D, Damage Tolerance and Fatigue Evaluation of Structure.
• AC 25.1309-1B, System Design and Analysis.
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AC 20-167B Appendix G
• AC 25.1329-1C, Approval of Flight Guidance Systems.
• AC 25.1322-1, Flightcrew Alerting.
• AC 25.1523-1, Minimum Flightcrew.
• AC 27-1B CHG 1-9, Certification of Normal Category Rotorcraft.
• AC 29-2C CHG 9, Certification of Transport Category Rotorcraft.
• AC 90-106B, Enhanced Flight Vision Systems.
• AC 120-29A, Criteria for Approval of Category I and Category II Weather Minima for Approach.
• AC 120-57C, Surface Movement Guidance and Control System.
• AC 120-62, Takeoff Safety Training Aid.
• AC 120-76E, Authorization for Use of Electronic Flight Bags.
• Order 8110.4C CHG 7, Type Certification.
• Order 8110.54A, Instructions for Continued Airworthiness Responsibilities, Requirements, and Contents.
• Order 8900.1A, Flight Standards Information Management.
G.3 Society of Automotive Engineers (SAE) International.
The following SAE Aerospace Recommended Practice (ARP) and Aerospace Standard (AS) documents are related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. The documents are available online at:
www.sae.org.
• ARP4101, Flight Deck Layout and Facilities.
• ARP4102, Flight Deck Panels, Controls and Displays.
• ARP4103A, Flight Deck Lighting for Commercial Transport Aircraft.
• ARP4105C, Abbreviations, Acronyms, and Terms for Use on the Flight Deck.
• ARP4754B, Guidelines for Development of Civil Aircraft and Systems.
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AC 20-167B Appendix G
• ARP4761A, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.
• ARP5287, Optical Measurement Procedures for Airborne Head Up Display (HUD).
• ARP5288, Transport Category Airplane Head Up Display (HUD) Systems.
• ARP5589, Human Engineering Considerations for Design and Implementation of Perspective Flight Guidance Displays.
• ARP5677, Human Engineering Considerations for Airborne Implementation of Enhanced Synthetic Vision Systems.
• AS8034C, Minimum Performance Standard for Airborne Multipurpose Electronic Displays.
• AS8055A, Minimum Performance Standard for Airborne Head Up Display (HUD).
G.4 ASTM Consensus Standard(s).
ASTM F3117M-24a, Standard Specification for Crew Interface in Aircraft is related to the guidance in this AC. FAA-accepted consensus standards, including any required changes for acceptance, are available online at faa.gov.
G.5 RTCA.
The following RTCA (formerly Radio Technical Commission for Aeronautics) document is related to the guidance in this AC. Unless otherwise specified, use the latest FAA-accepted revision for guidance. If the document is revised after publication of this AC, you should verify that the FAA accepts the subsequent revision or update as an acceptable form of guidance. This document can be ordered online at rtca.org.
• DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment.
• DO-178C, Software Considerations in Airborne Systems and Equipment Certification.
• DO-200, Standards for Processing Aeronautical Data.
• DO-254, Design Assurance Guidance for Airborne Electronic Hardware.
• DO-276B, User Requirements for Terrain and Obstacle Data.
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