Appendix H H-1 APPENDIX H. ADDITIONAL PART 23 CONSIDERATIONS FOR ENHANCED VISION
SYSTEM/OR SYNTHETIC VISION SYSTEM FOR SITUATION AWARENESS ONLY H.1 Introduction.
Synthetic vision may be so compelling that pilots may try to use it beyond the intended function. Current synthetic vision systems may not offer the depth/distance cueing necessary to be used for terrain avoidance. Another way of saying this is that error margins may still be too large to use any synthetic vision system alone. Current systems should be used with approved flight and navigation information. If other systems are not included to augment the synthetic vision system for terrain awareness, the applicant should show that the error margins due to field of view size, depth perception, resolution of the database used, resolution of the display, update rate of the display, and any other factors are small enough that synthetic vision alone is adequate for terrain awareness in all flight conditions expected. Display size constraints may result in a “compressed” display that has the potential to cause misleading altitude and range estimation. In addition, cumulative errors from GPS, terrain databases, and barometric altimetry systems may contribute to misleading distance and height cues.
Adequate mitigation should be provided to avoid the effects of such hazards. Such mitigation may be incorporated in the design or may include training or procedures to use other navigation sources. However, it is unwise to depend solely on Aircraft Flight Manual (AFM) limitations.
H.2 Terrain Alerting.
Any airplane equipment incorporating a synthetic vision system should also provide some type of terrain warning for pilots. The terrain warning feature should be incorporated on the Multifunction Display (MFD) or separate display unless the applicant can demonstrate that the feature is effective on the PFD. Synthetic vision systems on the PFD should provide adequate altitude and distance cues if used for terrain warning.
H.2.1 Applicants may use TSO-C151c, Class A, B, or C standards as applicable. Applicants may develop their own terrain warning system. However, the option of developing a terrain warning system is only available when there is not a specific carriage requirement for TAWS or HTAWS; it is not a substitute for any TAWS or HTAWS regulatory requirement. Applicants who want to develop their own terrain warning system should include:
A one-minute caution and 30-second warning if the airplane’s current flight path will collide with terrain or an obstacle.
Aural call-out for both the caution and the warning (CAUTION – TERRAIN, TERRAIN; WARNING – TERRAIN, TERRAIN).
Terrain impact region highlighted on the moving map.
Appendix H H-2 A safety margin or buffer of at least 100 feet for cumulative errors in both the GPS altitude and terrain database.
A terrain database/DEM developed using the criteria in RTCA DO-200A, Standards for Processing Aeronautical Data, dated September 28, 1998.
The synthetic vision display must not provide any information that is in conflict with or incompatible with either the terrain warning or terrain awareness functions of the TAWS or HTAWS.
H.3 Moving Map Display that Corresponds to and Complements Synthetic Vision PFD Display.
H.3.1 Synthetic vision depictions on the PFD have the potential to provide pilots with enhanced terrain and landmark awareness during non-precision and precision approaches. However, the display may not provide depth perception and may not provide a field-of-view for pilots to know what is to the left and right of the display view area. When viewing the terrain on a limited field-of-view display, pilots may mistakenly infer the location of the aircraft relative to the terrain.
H.3.2 There should be a second, complementary plan view display. The second display should depict the same terrain, obstacles, and features that appear on the PFDs synthetic vision display. This complementary display mitigates the lack of depth perception and FOV limitations on the typical synthetic vision display. This display should be the navigation display, but it could also be an MFD or a third, separate display. Ideally, the TAWS OR HTAWS or terrain alerting system should be part of this display (unless incorporated into the PFD) so that hazardous terrain or obstacles are highlighted.
H.4 Minimums Audio Callout Capability.
Applicants are encouraged to incorporate either a pilot selectable or automatic altitude alert with audio callout to remind pilots they are approaching minimums. Pilots may “see” the runway environment on their synthetic vision display and continue below minimums inadvertently because they were so intent on following the approach guidance. This scenario is similar to pilots fixating on a flight director and descending below minimums. Alerting pilots that they are nearing minimums reduces the opportunity for this situation to occur.
H.5 Digital Evaluation Model (DEM) Resolution.
The DEM resolution is one factor that determines how well the synthetic vision terrain depiction will match the terrain environment. NASA experiments have shown that a terrain resolution of 30-arc-seconds “rounds off” the terrain peaks and fills in valleys.
This makes the terrain appear less hazardous for the peaks than it is and potentially reduces some safety benefit. Conversely, for the valleys, the terrain appears higher and is therefore conservative. The same set of NASA experiments pointed out that even
Appendix H H-3 though pilots preferred terrain created using higher resolutions (one and three-arcseconds), a synthetic vision display using a 30-arc-second database could provide more situation awareness (and, therefore, safety) than the conventional instrument panel.
Therefore, we had historically considered 30-arc-second resolution the minimum safety standard for synthetic vision displays. This allowed for the introduction of synthetic vision systems given the technology limitations. But technology has surpassed the need to allow as low a minimum resolution. New systems should meet 15 arc sec or better.
Current systems do very well at twice the resolution minimum, but we want to encourage applicants to use the highest resolutions available in unclassified databases.
Applicants may also consider using very high resolution databases near airports while reducing the resolution in the rest of the database. More importantly, applicants should clearly define the resolution and measuring units of the DEM used by their synthetic vision system in the AFMS and the pilots’ handbooks so that pilots can understand any visual limitation caused by resolution limits.
Note: The DEM resolution needed on a synthetic vision display depends on the intended function of that display. Applicants need to consider how they are going to use the terrain database information for their synthetic vision display, and this information should be given to the FAA at the beginning of a synthetic vision certification program. Common elevation references are average elevation, maximum elevation, and sometimes, the elevation of the geometric center of the area. As postspacing increases, the difference between the DEM value and the actual elevation of a point within a cell may differ significantly. The elevations used for a synthetic vision display should be conservative; use the highest elevation for a given cell. This concept is identical to the current sectional charts labeling the highest elevation in the given quadrangle (square sector) of latitude and longitude.
H.6 Aircraft Flight Manual Supplement (AFMS).
The AFMS should contain limitations for pilots on use of the applicant’s system. These limitations should be explained in detail. Warnings, cautions, and notes should also address the proper use and potential misuse of the display for terrain awareness and avoidance.
H.7 SVS Unusual Attitude Recovery.
Historically, the FAA required all but essential flight information is removed from the PFD in unusual attitudes. This “decluttering” was meant to aid pilots in recovering the aircraft. Therefore, the first synthetic vision systems removed the synthetic depiction and reverted to the traditional “blue-over-brown” display during unusual attitudes.
Based on a past report, the FAA Civil Aeronautical Medical Institute (CAMI) observed little performance difference between recoveries with and without the synthetic depiction. Furthermore, there was a possibility pilots might be temporarily confused by the significant change to their primary attitude display. Therefore, applicants should consider leaving the synthetic vision depiction on the PFD for unusual attitude recovery. The SVS update rate will be evaluated in flight test against FAA Practical Test Standard maneuvers.
Appendix H H-4 H.7.1 Some indication of both sky and ground should always be visible on the PFD for use in initiating unusual attitude recovery.
H.7.2 Pilots should be able to initiate a recovery toward the correct horizon and altitude within one second of recognition.
Note: For example, a test scenario could include climbing with a large mountain or plateau in the background into a stall condition or descending into rising terrain with decreasing airspeed into a stall condition.
H.7.3 The artificial horizon line and other attitude-relate symbology (for example, aircraft symbol and pitch ladder) should be very prominent and highly visible against all possible backgrounds and symbology, including the assignment of a level of priority over other symbology on the display commensurate with its importance.
H.8 Pilot Evaluation.
There are hundreds of variables that can distinguish one display system from another.
Depending on the design implementation, a synthetic vision system might not provide a safety improvement. Because of the number of variables, a thorough FAA pilot evaluation will be necessary for the first implementation of any synthetic vision display system. Less FAA involvement may be possible on subsequent installations or system upgrades. Often, it is useful to gather subjective pilot assessments of the synthetic vision displays. Questionnaires used with flight evaluations and/or simulation are good tools to use for pilot assessment, but they need to be specific rather than merely solicit general impressions. Accepted and proven evaluation protocol, measures, and scales should be used where applicable to ensure the integrity of the evaluation process. The questions should target specific information presented on the display, its intended function, and whether it is usable for flight tasks required for typical instrument and commercial ratings. Besides using FAA pilots (including Designated Engineering Representative (DER) pilots), the applicant should consider conducting assessments with representative end user/operational pilots. Applicants should coordinate plans for any pilot evaluation with the responsible ACO.
Appendix I I-1 APPENDIX I. DEFINITIONS AND ACRONYMS I.1 Definitions I.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.
I.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).
I.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.
I.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).
I.1.5 Conformal (AC 25-11B) - Refers to displayed graphic information that is aligned and scaled with the outside view.
I.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.
I.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.
Appendix I I-2 I.1.8 Ego-centric - Used to define the view of a display image that correlates to inside the aircraft. One example is what the flight crew would see out the window from a forward facing perspective.
I.1.9 Enhanced Flight Visibility (EFV) (14 CFR § 1.1) - The average forward horizontal distance, from the cockpit 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 enhanced flight vision system.
I.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.
I.1.11 Enhanced Vision System (EVS) - 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, such as a forward looking infrared, millimeter wave radiometry, millimeter wave radar, low light level image intensifying.
Note 1: EASA uses term “EVS” as equivalent to FAA description of “EFVS.”
Note 2: Unlike an EFVS, an EVS does not necessarily provide the additional flight information/symbology required by 14 CFR § 91.176, might not use a head-up display 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 14 CFR § 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 the minimum descent altitude (MDA) or decision height (DH).
I.1.12 Equivalent Display - In the context of 14 CFR § 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.
Displays sensor-derived imagery conformal (as defined in SAE AS 8055) with the pilots 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.
Appendix I I-3 I.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.
I.1.14 Eye Reference Point (ERP) - The ERP is the point in the cockpit that allows for a finite reference enabling the precise determination of geometric entities that define the layout of the cockpit and displays.
I.1.15 Field of Regard (FOR) (SAE ARP 5677) - The angular extent of the external world that is represented on a display.
I.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. AC 25-11B provides the following diagram for primary field of view. See Figure 4 below.
Figure 4. Field of View I.1.17 Flare Guidance - Provides explicit command guidance for the pilot to flare the aircraft.
I.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 maneuver 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.
I.1.19 Flicker (RTCA/DO-315A) - High frequency luminance variations.
I.1.20 Flight Path Angle Reference Cue - Pilot selectable reference cue on the pitch scale displaying the desired approach angle.
Appendix I I-4 I.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.
I.1.22 Flight Visibility (14 CFR § 1.1) - The average forward horizontal distance, from the cockpit 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.
I.1.23 Head Up Display (HUD) (AC 25.1329-1C) - A transparent optical display system located level with and between the pilot and the forward windscreen. The HUD displays a combination of control, performance, navigation, and command information superimposed on the external field of view. It includes the display element, sensors, computers and power supplies, indications and controls. It is integrated with airborne attitude, air data and navigation systems, and as a display of command information is considered a component of the flight guidance system.
I.1.24 IFR conditions (14 CFR § 1.1) - Weather conditions below the minimum for flight under visual flight rules.
I.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.
I.1.26 Jitter (RTCA/DO-315A) - High frequency positional oscillations.
I.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.
I.1.28 Minimum Descent Altitude (14 CFR § 1.1) - The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach or during circleto-land maneuvering in execution of a standard instrument approach procedure, where no electronic glide slope is provided.
I.1.29 Noise Equivalent Power (NEP) - Measure of the sensitivity of an optical detector or detector system.
I.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.
I.1.31 Non-Uniformity Correction (NUC) - Calibration of a detector utilizing more than one detector element.
I.1.32 Precision Approach Procedure (14 CFR § 1.1) - A standard instrument approach procedure in which a precision lateral and vertical path is provided.
I.1.33 Primary Flight Display (PFD) - The displays used to present primary flight information.
Appendix I I-5 I.1.34 Rmax. - The maximum range the radar can detect.
I.1.35 Situation Information (AC 120-29A, Criteria for Approval of Category I and Category II Weather Minima for Approach,) - Information that directly informs the pilot about the status of the aircraft system operations or specific flight parameters including flight path.
I.1.36 Synthetic Vision (14 CFR § 1.1) - 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.
I.1.37 Synthetic Vision System (SVS) (AC 25.1329-1C) - An electronic means to display a computer-generated image of the applicable external topography from the perspective of the flight deck that is derived from aircraft attitude, altitude, position, and a coordinate-referenced database.
Note: “Topography” defined as 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.
I.1.38 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.
I.1.39 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.
I.1.40 Visual References - Visual information the pilot derives from the observation of realworld cues, out the flight deck window, used as a primary reference for aircraft control or flight path assessment.
I.2 Acronyms.
Acronym Phrase AC Advisory circular ACO Aircraft certification office AFM Aircraft flight manual BIT Built in test CVS Combined vision system DA Decision altitude DEM Digital elevation model DH Decision height DTED Digital terrain elevation data EASA European Aviation Safety Agency
Appendix I I-6 Acronym Phrase EFB Electronic flight bag EFIS Electronic flight instrument system EFVS Enhanced flight vision system EMI Electromagnetic interference EVS Enhanced vision system FAA Federal Aviation Administration FHA Functional hazard analysis FLIR Forward looking infrared 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 HIRF High intensity radiated fields 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 MDH Minimum descent height MFD Multi-function display ND Navigation display NETD Noise equivalent temperature difference NUC Non-uniformity correction PFD Primary flight display PIO Pilot Induced Oscillation RFM Rotorcraft flight manual RVR SSA Runway Visual Range System safety analysis STC Sensitivity time control; supplemental type certificate SVS Synthetic vision system TAWS Terrain awareness and warning system TC Type certificate TCH Threshold crossing height TDZE Touchdown zone elevation
Appendix J J-1 APPENDIX J. RELATED PUBLICATIONS J.1 Related Publications.
J.1.1 FAA Documents:
J.1.1.1 Order 8110.4C, Type Certification.
J.1.1.2 Order 8110.54A, Instructions for Continued Airworthiness Responsibilities, Requirements, and Contents.
J.1.1.3 AC 23-18, Installation of Terrain Awareness and Warning System (TAWS) Approved for Part 23 Airplanes.
J.1.1.4 AC 23.1309-1E, System Safety Analysis and Assessment for Part 23 Airplanes.
J.1.1.5 AC 23.1311-1C, Installation of Electronic Display in Part 23 Airplanes.
J.1.1.6 AC 25-11B Electronic Flight Deck Displays.
J.1.1.7 AC 25-23, Airworthiness Criteria for the Installation Approval of a Terrain Awareness and Warning System (TAWS) for Part 25 Airplanes.
J.1.1.8 AC 25.571-1D Damage Tolerance and Fatigue Evaluation of Structure J.1.1.9 AC 25.629-1B Aeroelastic Stability Substantiation of Transport Category Airplanes.
J.1.1.10 AC 25.1309-1A, System Design and Analysis.
J.1.1.11 AC 25.1329-1C, Approval of Flight Guidance Systems.
J.1.1.12 AC 25.1523-1, Minimum Flightcrew.
J.1.1.13 AC 27-1B, Certification of Normal Category Rotorcraft.
J.1.1.14 AC 29-2C, Certification of Transport Category Rotorcraft.
J.1.1.15 AC 90-106A, Enhanced Flight Vision Systems J.1.1.16 AC 120-29A, Criteria for Approval of Category I and Category II Weather Minima for Approach.
J.1.1.17 AC 120-57A, Surface Movement Guidance and Control System.
J.1.1.18 AC 120-76C, Guidelines for the Certification, Airworthiness, and Operational Use of Electronic Flight Bags.
Appendix J J-2 J.1.1.19 FAA HUD, Certification Working Paper PS-ANM100-2001-0085.
J.1.2 RTCA, Inc. Documents J.1.2.1 DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment.
J.1.2.2 DO-178C, Software Considerations in Airborne Systems and Equipment Certification.
J.1.2.3 DO-200A, Standards for Processing Aeronautical Data.
J.1.2.4 DO-254, Design Assurance Guidance for Airborne Electronic Hardware.
J.1.2.5 DO-276B, User Requirements for Terrain and Obstacle Data.
J.1.2.6 DO-309, Minimum Operational Performance Standards (MOPS) for Helicopter Terrain Awareness and Warning System (HTAWS) Airborne Equipment.
J.1.2.7 DO-315A, Minimum Aviation System Performance Standards (MASPS) for Enhanced Vision Systems, Synthetic Vision Systems, Combined Vision Systems, and Enhanced Flight Vision Systems.
J.1.3 SAE International Documents.
J.1.3.1 ARP 4101, Flight Deck Layout and Facilities.
J.1.3.2 ARP 4102, Flight Deck Panels, Controls and Displays.
J.1.3.3 ARP 4103A, Flight Deck Lighting for Commercial Transport Aircraft.
J.1.3.4 ARP 4105C, Abbreviations, Acronyms, and Terms for Use on the Flight Deck.
J.1.3.5 ARP 4754A, Guidelines for Development of Civil Aircraft and Systems J.1.3.6 ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment J.1.3.7 ARP 5288, Transport Category Airplane Head Up Display (HUD) Systems.
J.1.3.8 ARP 5589, Human Engineering Considerations for Design and Implementation of Perspective Flight Guidance Displays.
J.1.3.9 ARP 5677, Human Engineering Considerations for Airborne Implementation of Enhanced Synthetic Vision Systems