Appendix 3
A3-4 Eye Reference Position (ERP) - A single spatial position located at or near the center of the HUD Eye Box. The HUD ERP is the primary geometrical reference point for the HUD.
Failure - An occurrence which affects the operation of a component, part, or element, such that it can no longer function as intended (this includes both loss of function and malfunction).
NOTE: Errors may cause failures but are not considered to be failures.
Failure Condition - A condition having an effect on the airplane and/or its occupants, either direct or consequential, which is caused or contributed to by one or more failures or errors, considering flight phase and relevant adverse operational or environmental conditions, or external events.
Field of View - The angular extent of the display that can be seen by either pilot with the pilot seated at either pilots station.
Flicker - An undesired, rapid temporal variation in the display luminance of a symbol, group of symbols, or a luminous field. It can cause discomfort for the viewer (such as headaches and irritation).
Flight Deck Design Philosophy - A high level description of the design principles that guide the designer and ensure a consistent and coherent interface is presented to the flightcrew.
Flight Path Angle (FPA) (also known as a Flight Path Symbol, Climb, Dive Angle, or “caged” (on the attitude indicator centerline) Flight Path Vector) - A dynamic symbol displayed on an attitude display that depicts the vertical angle relative to the artificial horizon, in the pitch axis, that the airplane is moving. A flight path angle is the vector resultant of the forward velocity and the vertical velocity. For most designs, the FPA is earth referenced, though some use air mass vectors. Motion of the FPA on the attitude display is in the vertical (pitch) axis only with no lateral motion.
Flight Path Vector (FPV) (also known as Velocity Vector or Flight Path Marker) - A dynamic symbol displayed on an attitude display that depicts the vector resultant of real-time flight path angle (vertical axis) and lateral angle relative to airplane heading created by wind drift and slip/skid. For most designs, the FPV is earth referenced, though some use air mass vectors which cannot account for wind effects
Foreseeable Conditions - The full environment that the display or the display system is assumed to operate within, given its intended function. This includes operating in normal, non-normal, and emergency conditions.
Appendix 3
A3-5 Format (See Figure A3-2) - An image rendered on the whole display unit surface. A format is constructed from one or more windows (see ARINC Specification 661).
FPV/FPA-referenced Flight Director (FD) - A HUD or HDD flight director cue in which the pilot “flies” the FPV/FPA cue to the FD command in order to comply with flight guidance commands. This is different from attitude FD guidance where the pilot “flies” the airplane (that is, pitch, boresight) symbol to follow pitch and roll commands.
Full-time Display - A dedicated continuous information display.
Functional Hazard Assessment - A systematic, comprehensive examination of airplane and system function to identify potential Minor, Major, Hazardous, and Catastrophic failure conditions that may arise as a result of malfunctions or failures to function.
Gray Scale - The number of incremental luminance levels between full dark and full bright.
Hazard - Any condition that compromises the overall safety of the airplane or that significantly reduces the ability of the flightcrew to cope with adverse operating conditions.
Hazardous – A hazardous failure condition reduces the operation of the airplane or the ability of the flightcrew to operate in adverse conditions to the extent that there would be:
• A large reduction in safety margins or functional capabilities;
• Physical distress or excessive workload such that the flightcrew cannot be relied upon to perform their tasks accurately or completely; or
• Serious or fatal injury to a relatively small number of the occupants other than the flightcrew.
Head Down Display (HDD) - A primary flight display located on the airplane’s main instrument panel directly in front of the pilot in the pilot’s primary field of view. The HDD is located below the windscreen and requires the flightcrew to look below the glareshield in order to use the HDD to fly the airplane.
Head Mounted Display (HMD) – A special case of HUD mounted on the pilot’s head.
Currently, there are not any HMDs used in part 25 installations, but guidance will be provided in the future, as needed.
Head Up Display (HUD) - 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
Appendix 3
A3-6 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.
HUD Design Eye Box - The three-dimensional area surrounding the design eye position, which defines the area, from which the HUD symbology and/or imagery are viewable.
Icon - A single, graphical symbol that represents a function or event.
Image Size - The viewing area (field) of the display surface.
• Direct View Display: The useful (or active) area of the display (for example, units cm x cm).
• Head Up Display: The total field of view (units usually in degrees x degrees).
(Total field of view defines the maximum angular extent of the display that can be seen by either eye allowing head motion within the eyebox (see SAE AS 8055).
Indication - Any visual information representing the status of graphical gauges, other graphical representations, numeric data messages, lights, symbols, synoptics, etc. to the flightcrew.
Information Update Rate - The rate at which new data is displayed or updated.
Interaction - The ability to directly affect a display by utilizing a graphical user interface (GUI) that consists of a control device (for example, a trackball), cursor, and “soft” display control that is the cursor target.
Latency - 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.
Layer - A layer is the highest level entity of the Display System that is known by a User Application.
Luminance - Visible light that is emitted from the display. Commonly-used units: footlamberts, cd/m2.
Major - A major failure condition reduces the operation of the airplane or the ability of the crew to operate in adverse conditions to the extent that there would be, for example:
• A significant reduction in safety margins or functional capabilities;
Appendix 3
A3-7
• A significant increase in crew workload or in conditions impairing crew efficiency;
• Discomfort to the flightcrew; or
• Physical distress to passengers or cabin crew, possibly including injuries.
Menu - A list of display options available for selection.
Message - A communication that conveys an intended meaning such as an alerting or data link message.
Minor - A minor failure condition would not significantly reduce airplane safety and would involve crew actions well within their capabilities. Minor failure conditions may include:
• A slight reduction in safety margins or functional capabilities;
• A slight increase in crew workload (such as routine flight plan changes); or
• Some physical discomfort to passengers or cabin crew.
Misleading Information - Incorrect information that is not detected by the flightcrew because it appears as correct and credible information under the given circumstances.
When incorrect information is automatically detected by a monitor resulting in an indication to the flightcrew, or when the information is obviously incorrect, it is no longer considered misleading. The consequence of misleading information will depend on the nature of the information, and the given circumstances.
Mode - The functional state of a display and/or control system(s). A mode can be manually or automatically selected.
MSG-3 - Maintenance Steering Group 3. A steering group sponsored by the Airline Transportation Association whose membership includes representatives from the aviation industry and aviation regulatory authorities.
Occlusion - Visual blocking of one symbol by another, sometimes called occulting.
Partitioning - A technique for providing isolation between functionally independent software components to contain and/or isolate faults and potentially reduce the effort of the software verification process.
Appendix 3
A3-8 Pixel - A display picture element which usually consists of three (red, green, blue) sub-pixels (also called dots on a cathode ray tube).
Pixel Defect - A pixel that appears to be in a permanently on or off-state.
Primary Flight Displays - The displays used to present primary flight information.
Primary Field of View (FOV) (See Figure A3-1) - Primary Field-of-View is based on the optimum vertical and horizontal visual fields from the design eye reference point that can be viewed with eye rotation only using foveal or central vision. The description below provides an example of how this may apply to head-down displays.
Appendix 3
A3-9
With the normal line-of-sight established at 15 degrees below the horizontal plane, the values for the vertical (relative to normal line-of-sight forward of the aircraft) are +/-15 degrees optimum, with +40 degrees up and -20 degrees down maximum.
Figure A3-1 Primary Field of View
Primary Flight Information - The information whose presentation is required by §§ 25.1303(b) and 25.1333(b), and arranged by § 25.1321(b).
Primary Flight Instrument - Any display or instrument that serves as the flightcrew’s primary reference of a specific parameter of primary flight information. For example, a centrally located attitude director indicator is a primary flight instrument because it is the flightcrew’s primary reference for pitch, bank, and command steering information.
Prompt - A method of cueing the flightcrew that some input or action is required.
Appendix 3
A3-10
Required Engine Indications - The information whose presentation is required by § 25.1305.
Reversionary - The automatic or flightcrew initiated (manual) relocation of display formats or windows following a display failure.
Shading - Shading is used as:
• A coding method for separating information, change in state, give emphasis, and depth information.
• A blending method between graphic elements (map displays, synthetic vision system).
Soft Control - Display element used to manipulate, select, or de-select information (for example, menus and soft keys).
Standby Display - A backup display that is used if a primary display malfunctions.
Status information - Information about the current condition of an airplane system and its surroundings.
Symbol - A symbol is a geometric form or alpha-numeric information used to represent the state of a parameter on a display. The symbol may be further defined by its location and motion on a display.
Synthetic Vision – A computer generated image of the external topography from the perspective of the flight deck. The image is derived from aircraft attitude, high-precision navigation solution, and terrain database terrain, obstacles, and relevant cultural features.
Synthetic Vision System – An electronic means to display a synthetic vision image of the external scene topography to the flightcrew.
Texturing - A graphic, pictorial effect used to give a displayed object or graphic a specific “look” (metallic, grassy, cloudy, etc.). Texture is used:
• As a coding method for separating information, change in state, give emphasis, and depth information.
• As a blending method between graphic elements (map displays, synthetic vision system).
• To enhance similarity between a synthetic image and the real world image.
Appendix 3
A3-11 Viewing Envelope - Total volume of space where the minimum optical performance of the display is met (for example, luminance, contrast, or chromaticity). For a direct view display it is the solid angle with respect to the normal of the display image and for a HUD a threedimensional volume (Eyebox).
Time Sharing – Showing different information in the same display area at different times.
Transparency - A means of seeing a background information element through a foreground information element. Transparency can alter the color perception of both the “front” element and the “back” element.
Viewing Angle – The angle between the normal line of sight (looking straight ahead) and the line from the eye to the object being viewed. The angle can be horizontal, vertical, or a composite of those two angles.
Window (See Figure A3-2) - A rectangular physical area of the display surface. A window consists of one or more layers (see ARINC Specification 661).
Figure A3-2 – Display Format
Windowing - The technique to create windows. Segmenting a single display area into two or more independent display areas or inserting a new display area onto an existing display.
Appendix 4 A4-1
Appendix 4 Acronyms Used in This AC
AC Advisory Circular ARAC Aviation Rulemaking Advisory Committee ARP Aerospace Recommended Practices AS Aerospace Standard CCD Curser Control Device CFR Code of Federal Regulations CRT Cathode Ray Tube DEP Design Eye Position EASA European Aviation Safety Agency EUROCAE European Organization for Civil Aviation Electronics FAA Federal Aviation Administration GUI Graphical User Interface HDD Head down Display HUD Head up Display JAA Joint Airworthiness Authority LCD Liquid Crystal Display SAE SAE International (formerly Society of Automotive Engineers) TCAS Traffic Alert and Collision Avoidance System
Appendix 5
A5-1 Appendix 5 Related Regulations and Documents
General
The following related documents are provided for information purposes and are not necessarily directly referenced in this AC.
The regulations and standards listed below are applicable to particular systems or functions which may have implications on the display system characteristics even though they do not explicitly state display requirements. It is not an exhaustive list, and the references should be reviewed to ensure currency of issue status, and to check for any others that may be applicable.
1. Regulations
The full text of 14 CFR can be downloaded from the Internet at http://www.gpoaccess.gov/nara.
A paper copy may be ordered from the Government Printing Office (GPO), Superintendent of Documents, Attn: New Orders, PO Box 371954, Pittsburgh, PA 15250-7954.
The following is a list of regulations/certifications that should be considered when certifying an electronic display system:
Section
Title
§ 25.143
Controllability and Maneuverability: General
§ 25.207 Stall warning
§ 25.672 Stability augmentation and automatic and power-operated systems
§ 25.677 Trim systems
§ 25.679 Control system gust locks
§ 25.699 Lift and drag device indicator
§ 25.703 Takeoff warning system
§ 25.729 Retracting mechanism
§ 25.771 Pilot compartment
Appendix 5
A5-2 Section
Title
§ 25.773
Pilot compartment view
§ 25.777 Cockpit controls
§ 25.779
Motion and effect of cockpit controls § 25.783 Fuselage doors
§ 25.812 Emergency lighting
§ 25.841 Pressurized cabins
§ 25.854 Lavatory fire protection
§ 25.857 Cargo compartment classification
§ 25.858 Cargo or baggage compartment smoke or fire detection systems
§ 25.859 Combustion heater fire protection
§ 25.863 Flammable fluid fire protection
§ 25.901 Powerplant: Installation
§ 25.903 Engines
§ 25.904 Automatic takeoff thrust control system (ATTCS)
§ 25.1001 Fuel Jettisoning System
§ 25.1019 Oil strainer or filter
§ 25.1141 Powerplant controls: General
§ 25.1165 Engine ignition systems
§ 25.1199 Extinguishing agent containers
§ 25.1203 Fire detector system
Appendix 5
A5-3 Section
Title
§ 25.1301 Equipment: Function and installation
§ 25.1303 Flight and navigation instruments
§ 25.1305 Powerplant instruments
§ 25.1309 Equipment, systems, and installations
§ 25.1316 System lightning protection
§ 25.1321 Arrangement and visibility
§ 25.1322 Warning, caution, and advisory lights
§ 25.1323 Airspeed indicating system
§ 25.1326 Pitot heat indication systems
§ 25.1327 Magnetic direction indicator
§ 25.1329 Automatic pilot system
§ 25.1331 Instruments using a power supply
§ 25.1333 Instrument systems
§ 25.1335 Flight director systems
§ 25.1337 Powerplant instruments
§ 25.1351 Electrical Systems and Equipment: General
§ 25.1353 Electrical equipment and installations
§ 25.1355 Distribution system
§ 25.1357 Circuit protective devices
§ 25.1381 Instrument lights