Appendix 1
A1-7 It should be easy and intuitive for the pilot to switch between FPV/FPA and attitude when necessary. The primary flight display of FPV/FPA symbology must not interfere with the display of attitude and there must always be attitude symbology at the top center of the pilot's primary field of view, as required by § 25.1321.
Airplane designs which display flight path symbology on the HUD and the HDD should use consistent symbol shapes (that is, the HUD FPV symbol looks like the HDD FPV).
In existing cases where an FPV is displayed head up and an FPA head down on an airplane, the symbols for each should not have the same shape. When different types of flight path indications may be displayed as head up and/or head down, the symbols should be easily distinguished to avoid any misinterpretation by the flightcrew. A mixture of the two types of flight path indications is not recommended due to possible misinterpretation by the flightcrew.
The normal FPV, the field-of-view limited FPV, and the caged FPV should each have a distinct appearance, so that the pilot is aware of the restricted motion or non-conformality.
Implementation of air mass-based FPV/FPA presentations should account for inherent limitations of air mass flight path computations.
Flight directors should provide some lateral movement to the lateral flight director guidance cue during bank commands.
To show compliance with §§ 25.1301(a), 25.1303(b)(5), and 25.143(b), the FPV/FPA FD design must:
1. Not have any characteristics that ma y lead to oscillatory control inputs;
2. Provide sufficiently effective and salien t cues to support all expected maneuvers in longitudinal, lateral, and directional axes, including recovery from unusual attitudes; and
3. Not have any inconsistencies betw een cues provided on the HUD and HDD displays that may lead to pilot confusion or have adverse affects on pilot performance.
Appendix 1
A1-8
Performance and system safety requirements for flight guidance systems are found in the following advisory circulars:
Document Number Title
AC 25.1329-1B Approval of Flight Guidance Systems
AC 120-28D Criteria for Approval of Category III Weather Minima for Takeoff, Landing, and Rollout
AC 120-29A Criteria for Approval of Category I and Category II Weather Minima for Approach
Appendix 2
A2-1 Appendix 2 Powerplant Displays
1. General At the time §25.1305 was adopted, flight deck powerplant displays were primarily a collection of dedicated, independent, full-time analog “round dial” type instruments. Typically, there was one display for each required indication. Today, flight deck powerplant displays are primarily electronic displays integrated with other flight deck displays on a few relatively large electronic display spaces. Throughout this technological evolution, the FAA has used certification issue papers and other guidance material to assure that this new technology, with its increased potential for common faults and the challenges of effectively sharing display space, did not adversely impact the timely availability and independence of the powerplant information required to meet the intent of §25.1305. This AC provides some of that guidance material.
To comply with one of the provisions of §25.1305, a display should provide all the instrument functionality of a full-time, dedicated analog type instrument as intended when the rule was adopted (see AC 20-88A, Guidelines on the Marking of Aircraft). The design flexibility and conditional adaptability of modern displays were not envisioned when § 25.1305 and § 25.1549 were initially adopted. In addition, the capabilities of modern control systems to automate and complement flightcrew functions were not envisioned. In some cases these system capabilities obviate the need for a dedicated full-time analog type instrument.
When making a compliance finding, all uses of the affected displays should be taken into consideration, including:
(1) Flight deck indications to support the approved operating procedures (§ 25.1585),
(2) Indications as required by the powerplant system safety assessments (§ 25.1309), and
(3) Indications required in support of the instructions for continued airworthiness (§ 25.1529).
For example:
Compliance with § 25.1305(c)(3) for the engine N2 rotor was originally achieved by means of a dedicated, full time analog instrument. This provided the continuous monitoring capability required to:
• Support engine starting (for example, typically used to identify fuel on point);
• Support power setting (for example, sometimes used as primary or back up parameter);
Appendix 2
A2-2
• “Give reasonable assurance that those engine operating limitations that adversely affect turbine rotor structural integrity will not be exceeded in service” as required by § 25.903(d)(2);
• Provide the indication of normal, precautionary, and limit operating values required by § 25.1549; as well as
• Support detection of unacceptable deterioration in the margin to operating limits and other abnormal engine operating conditions as required to comply with §§ 25.901,
25.1309, etc.
As technology evolved full authority digital engine controls (FADECs) were introduced. The FADECs were designed with the ability to monitor and control engine N2 rotor speed as required to comply with § 25.903(d)(2). Additionally, engine condition monitoring programs were introduced and used to detect unacceptable engine deterioration. Flight deck technology evolved such that indications could be displayed automatically to cover abnormal engine operating conditions. The combination of these developments obviated the need for a full time analog N2 rotor speed indication, in accordance with the guidance found in Chapter 6, paragraph 36c(3) of this AC.
2. Design Guidelines
Safety-related engine limit exceedances should be indicated in a clear and unambiguous manner.
Flightcrew alerting is addressed in the ARAC recommendations for revising the current § 25.1322.
If an indication of significant thrust loss is provided it should be presented in a clear and unambiguous manner.
In addition to the failure conditions listed in Chapter 4 of this AC, the following design guidelines should be considered:
1. For single failures leading to the non-recoverable loss of any indications on an engine, sufficient indications should remain to allow continued safe operation of the engine. (See §§ 25.901(b)(2), 25.901(c), and 25.903(d)(2)).
2. No single failure could prevent the continued safe operation of more than one engine or require immediate action by any flightcrew member for continued safe operation. (See §§ 25.901(c), 25.903(b), and 25.1309(b)).
3. Engine indications needed during engine re-start should be readily available after an engine out event. (See §§ 25.901(b)(2), 25.901(c) 25.903(d)(2), 25.903(e), 25.1301,
25.1305, 25.1309, and Chapter 6, paragraph 36c(3) of this AC).
Appendix 3
A3-1 Appendix 3 Definitions
Air Mass System - An air mass-based system that provides a heading/airspeed/vertical velocity derived flight path presentation. It depicts the flight path through an air mass, will not account for air mass disturbances such as wind drift and windshear and, therefore, cannot be relied on to show the flight path relative to the earth’s surface.
Alert – A generic term used to describe a flight deck indication meant to attract the attention of and identify to the flightcrew a non-normal operational or airplane system condition. Warnings, Cautions, and Advisories are considered to be alerts.
Annunciation - A visual, auditory, or tactile stimulus used to attract a flightcrew member’s attention.
Architecture - The manner in which the components of a display or display system are organized and integrated.
Basic T - The arrangement of primary flight information as required by § 25.1321(b); including attitude, airspeed, altitude, and direction information.
Brightness - The perceived or subjective luminance. This should not be confused with luminance.
Bugs - A symbol used to mark or reference other information such as heading, altitude, etc.
Catastrophic - Failure conditions that result in multiple fatalities, usually with the loss of the airplane. (Note: In previous versions of § 25.1309 and the associated advisory material a “catastrophic failure condition” was defined as a failure condition that would prevent continued safe flight and landing.)
Chrominance - The quality of a display image that includes both luminance and chromaticity and is a perceptual construct subjectively assessed by the human observer.
Chromaticity - Color characteristic of a symbol or an image defined by its u’, v’ coordinates (See Commissions Internationale de L’Eclairage publication number 15.3, Colorimetry, 2004).
Clutter - Excessive number and/or variety of symbols, colors, or other information on a display that may reduce flightcrew access or interpretation time, or decrease the probability of interpretation error.
Coasting Data - Data that is not updated for a defined period of time.
Appendix 3
A3-2
Coding - The use of assigning special meanings to some design element or characteristic (such as numbers, letters, symbols, auditory signals, colors, brightness, or variations in size) to represent information in a shorter or more convenient form.
Coding Characteristics - Readily identifiable attributes commonly associated with a design element that provide special meaning and differentiate the design elements from each other; for example size, shape, color, motion, location, etc.
Color Coding - The structured use of color to convey specific information, call attention to information, or impose an organizational scheme on displayed information.
Command Information - Displayed information directing a control action.
Compact Mode - In display use, this most frequently refers to a single, condensed display presented in numeric format that is used during reversionary or failure conditions.
Conformal - Refers to displayed graphic information that is aligned and scaled with the outside view.
Contrast Ratio -
For HUD - Ratio of the luminance over the background scene (see SAE AS 8055).
For HDD - Ratio of the total foreground luminance to the total background luminance.
Criticality - Indication of the hazard level associated with a function, hardware, software, etc., considering abnormal behavior (of this function, hardware, software) alone, in combination, or in combination with external events.
Design Eye Position - The position at each pilot's station from which a seated pilot achieves the required combination of outside visibility and instrument scan. The design eye position (DEP) is a single point selected by the applicant that meets the requirements of §§ 25.773(d), 25.777(c), and 25.1321 for each pilot station. It is normally a point fixed in relation to the aircraft structure (neutral seat reference point) at which the midpoint of the pilot’s eyes should be located when seated at the normal position. The DEP is the principal dimensional reference point for the location of flight deck panels, controls, displays, and external vision.
Display Element – A basic component of a display, such as a circle, line, or dot.
Display Refresh Rate - The rate at which a display completely refreshes its image.
Appendix 3
A3-3 Display Resolution - Size of the minimum element that can be displayed, expressed by the total number of pixels or dots per inch (or millimeter) of the display surface.
Display Response Time - The time needed to change the information from one level of luminance to a different level of luminance. Display response time related to the intrinsic response (time linked to the electro-optic effect used for the display and the way to address it).
Display Surface/Screen - The area of the display unit that provides an image.
Display System - The entire set of avionic devices implemented to display information to the flightcrew. This is also known as an electronic display system.
Display Unit - Equipment that is located in the flight deck, in view of the flightcrew, that is used to provide visual information. Examples include a color head down display and a head up display projector and combiner.
Earth Referenced System - An inertial-based system which provides a display of flight path through space. In a descent, an earth-referenced system indicates the relationship between the flight path and the terrain and/or the artificial horizon.
Enhanced Flight Vision System (EFVS) - 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 millimeter wave radiometry, millimeter wave radar, and low light level image intensifying.
Enhanced Vision System (EVS) - An electronic means to provide a display of the forward external scene topography through the use of imaging sensors, such as forward looking infrared, millimeter wave radiometry, millimeter wave radar, and low light level image intensifying.
NOTE: An EFVS is an EVS that is intended to be used for instrument approaches under the provisions of 14 CFR 91.175 (l) and 91.175 (m), and must display the imagery with instrument flight information on a HUD.
Extremely Improbable - An extremely improbable failure condition is so unlikely that it is not anticipated to occur during the entire operational life of all airplanes of one type.
Extremely Remote - An extremely remote failure condition is not anticipated to occur to each airplane during its total life, but may occur a few times when considering the total operational life of all airplanes of that type.
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.