CHAPTER 1. INTRODUCTION
1.1 Purpose.
This advisory circular (AC) provides guidance for showing compliance with certain requirements of Title 14, Code of Federal Regulations (CFR) part 25, as well as general guidance for the design, installation, integration, and approval of electronic flight deck displays, components, and systems installed in transport category airplanes.
Appendix A of this AC provides additional guidance for displaying primary flight information (required by §§ 25.1303(b) and 25.1333(b)), and appendix B of this AC provides additional guidance for powerplant displays.
1.2 Applicability.
1.2.1 The guidance provided in this AC is directed to airplane and avionics manufacturers, modifiers, and operators of transport category airplanes.
1.2.2 This material in this AC is neither mandatory nor regulatory in nature and does not constitute a regulation. It describes acceptable means, but not the only means, for showing compliance with the applicable regulations. The Federal Aviation Administration (FAA) will consider other methods of showing compliance that an applicant may elect to present. While these guidelines are not mandatory, they are derived from extensive FAA and industry experience in determining compliance with the relevant regulations. If, however, we become aware of circumstances that convince us that following this AC would not result in compliance with the applicable regulations, we will not be bound by the terms of this AC, and we may require additional substantiation or design changes as a basis for finding compliance.
Applicants for a technical standard order (TSO) should consider following the guidance in this AC when the TSO requirements do not provide sufficient guidance.
1.2.3 This material in this AC does not change or create any additional regulatory requirements, nor does it authorize changes in, or permit deviations from, regulatory requirements.
1.3 Cancellation.
This AC cancels AC 25-11A, Electronic Flight Display Systems, dated June 21, 2007.
1.4 General.
1.4.1 This AC applies to the design, integration, installation, and certification approval of electronic flight deck displays, components, and systems for transport category airplanes. As a minimum, this includes—
• General airworthiness considerations,
• Display system and component characteristics, 1-1
• Safety and criticality aspects,
• Functional characteristics,
• Display information characteristics,
• Guidance to manage display information,
• Flightcrew interface and interactivity, and
• Airworthiness approval (means of compliance) considerations.
.4.2 Table 1-1 lists the topics within the guidance of this AC. Table 1-2 lists the topics within the guidance of this AC.
Table 1-1. Topics Within the Guidance of this AC 1 not Topics Electronic pilot displays, including single-function and multi-function displays.
Display features and functions that are intended for use by the pilot.
Display functions not intended for use by the pilot if they may interfere with the
pilot’s flying duties.
Display aspects of Class III electronic flight bag (installed equipment).
Controls associated with the electronic displays covered in this AC. These controls
include hard controls (physical buttons and knobs) and soft controls (virtual or programmable buttons and knobs, generally controlled through a cursor device or line select keys).
Electronic standby displays.
Head-up displays (HUDs).
Enhanced and synthetic vision systems.
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Table 1-2. Topics Outside the Guidance of this AC Topics Display functions not intended for use by the pilot.
In-flight entertainment displays.
Flight attendant displays.
Maintenance terminals, even if they are in the flight deck, but not intended for use
by the pilots.
Head-mounted displays used by pilots.
Displays in the flightcrew rest area.
Handheld or laptop items (not installed equipment).
Class I and Class II electronic flight bags.
Electromechanical instruments.
Auditory “displays” (for example, aural alerts) and tactile “displays” (for example,
stick shaker).
Flight controls, throttles, and other (hard) controls not directly associated with the
electronic displays.
1.4.3 Other advisory material is available for use in establishing guidance for specific functionality and characteristics provided by electronic displays. For example, AC 25-23, Airworthiness Criteria for the Installation Approval of a Terrain Awareness and Warning System (TAWS) for Part 25 Airplanes, describes a means for airworthiness approval of TAWS, and includes guidance on the display of TAWS. This revised AC 25-11B is not intended to replace or conflict with any existing AC. Its purpose is to provide general, high-level guidance for electronic displays in the flight deck. Conflicts between this AC and other advisory material, if any, will be resolved on a case-by-case basis, in agreement with the FAA. In those cases, the more specifically applicable material should be followed.
1.4.4 The combination of the guidance material in this AC, the Aviation Rulemaking Advisory Committee (ARAC) recommendations for adding a new regulation to 14 CFR part 25 and revising two existing part 25 regulations, and the associated guidance material for the ARAC recommendations, is intended to represent the design characteristics and techniques that are— 1-3
• Widely accepted in the aviation industry,
• Relevant to the regulatory requirements, and
• Can be reasonably applied to transport airplane certification programs for electronic flight deck displays.
1.4.5 The ARAC recommendations include revising the existing § 25.1309, Equipment, systems, and installations; and § 25.1333(b), Instrument systems. It is the FAA’s intent that the information in this AC does not duplicate or conflict with the information provided in the guidance material that will possibly be created as a result of the ARAC recommendations for §§ 25.1309 and 25.1333(b).
1.4.5.1 For information about the ARAC recommendation for § 25.1309, see ARAC Task 2 - System Design and Analysis Harmonization and Technology Update at the FAA website.
1.4.5.2 For information about the ARAC recommendation for § 25.1333(b), see ARAC Task 2 - Cockpit Instrument System at the FAA website.
Section 25.1333(b) is one part of the recommendations for this task.
1.5 Definitions of Terms Used in this AC.
1.5.1 For the purposes of this AC, a “display system” includes no and software components but also the entire set of avionic d display information to the flightcrew. Hardware and softwa t only the display hardware evices implemented to re components of other systems that affect displays, display functions, or display controls should take into account the display aspects of this AC. For example, this AC would be applicable to a display used when setting the barometric correction for the altimeter, even though the barometric set function may be part of another system.
1.5.2 For the purposes of this AC, “foreseeable conditions” means the full environment in which the display or the display system is assumed to operate, given its intended function. This includes operating in normal, non-normal, and emergency conditions.
1.5.3 Definitions of technical terms used in this AC can be found in appendix C of this AC.
The acronyms used throughout this document are included in appendix D of this AC. A list of applicable regulations, related guidance, and industry material is included in appendix E of this AC.
1.6 Background.
1.6.1 Electronic displays can present unique opportunities and challenges to the design and certification process. In many cases, showing compliance with regulatory requirements related to the latest flight deck display system capabilities has been subject to a great deal of interpretation by applicants and the FAA. At the time the first electronic displays were developed, they were direct replacements for the conventional 1-4
electromechanical components. The initial release of AC 25-11 established guidance for the approval of cathode ray tube (CRT) based electronic display systems used for guidance, control, or decision-making by the flightcrews of transport category airplanes.
This initial guidance was appropriate for CRTs, but additional guidance was needed to update AC 25-11 to address new technologies. Additional appendices have been added as new types of displays have been developed. Appendix F includes guidance for HUDs, and appendix G includes guidance for weather displays.
1.6.2 The FAA and European Aviation Safety Agency (EASA) have established a number of regulatory requirements intended to improve aviation safety by requiring that the flight deck design have certain capabilities and characteristics. The approval of flight deck displays and display systems has typically been addressed by invoking many rules that are specific to certain systems, or to rules with general applicability such as §§ 25.1301(a), 25.771(a), and 25.1523. Thus, this AC provides guidance related to these and other applicable regulations.
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CHAPTER 2. ELECTRONIC DISPLAY SYSTEM OVERVIEW
2.1 General.
The following paragraphs provide guidance that applies to the overall electronic display system. This chapter, together with chapters 1 through 7 of this AC, provides compliance objectives and design guidance. Chapter 8 provides general guidance on how to show compliance for approval of electronic display systems. The material in chapters 2 through 9 and appendices A and B of this AC constitutes an overall method of compliance for the approval of an electronic display system.
2.2 Design Philosophy.
The applicant should establish, document, and follow a design philosophy for the display system that supports the intended functions (§ 25.1301). The documented design philosophy may be included as part of a system description, certification plan, or other document that is submitted to the FAA during a certification project. The design philosophy should include a high level description of (1) information presentation,
(2) color of electronic displays, (3) information management, (4) interactivity, and
(5) redundancy management.
2.2.1 General Philosophy of Information Presentation.
For example, is a “quiet, dark” flight deck philosophy used or is some other approach used?
2.2.2 Color Philosophy on the Electronic Displays.
The meaning and intended interpretation of different colors. For example, does magenta always represent a constraint?
2.2.3 Information Management Philosophy.
For example, when should the pilot take an action to retrieve information or is it brought up automatically? What is the intended interpretation of the location of the information?
2.2.4 Interactivity Philosophy.
For example, when and why is pilot confirmation of actions requested? When is feedback provided?
2.2.5 Redundancy Management Philosophy.
For example, how are single and multiple display failures accommodated? How are power supply and data bus failures accommodated?
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2.3 Human Performance Considerations.
2.3.1 The applicant should establish and document the following human performance elements when developing a display system:
• Flightcrew workload.
• Flightcrew training time to become sufficiently familiar with using the display.
• The potential for flightcrew error.
2.3.2 A high workload or excessive training time may indicate a display design that is difficult to use, requires excessive concentration, or may be prone to flightcrew errors.
Compliance considerations are included in chapter 8 of this AC.
2.4 Addressing Intended Function in the Certification Plan.
The certification plan should identify the appropriate part 25 rules. An important part of the certification plan will be the system description(s) and all intended functions, including attitude, altitude, airspeed, engine parameters, horizontal situation display, etc. To demonstrate compliance with § 25.1301(a), an applicant must show that the design is appropriate for its intended function. The applicant’s description of intended function needs to be sufficiently specific and detailed for the FAA to be able to evaluate that the system is appropriate to its intended function. The rule § 25.1302 and AC 25.1302-1, Installed Systems and Equipment for Use by the Flightcrew, provide additional information on intended function requirements and guidance. General and/or ambiguous intended function descriptions are not acceptable (for example, a function described only as “situation awareness”). Some displays may be intended to be used for situation awareness, but that term needs to be clarified or qualified to explain what type of specific situation awareness will be provided. More detailed descriptions may be warranted for designs that are new, novel, highly integrated, or complex. Many modern displays have multiple functions and applicants should describe each intended function.
A system description is one place to document the intended function(s).
2.5 Non-Interference with Flying Duties.
Display systems and display components that are not intended for use by the flightcrew (such as maintenance displays) should not interfere with the flying duties of the flightcrew.
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CHAPTER 3. ELECTRONIC DISPLAY HARDWARE
3.1 Display Hardware Characteristics.
The following paragraphs provide general guidance and a means of compliance for electronic display hardware with respect to its basic visual, installation, and power bus transient handling characteristics. A more detailed set of display hardware characteristics can be found in the following SAE International (formerly the Society of Automotive Engineers) documents:
• For electronic displays, SAE Aerospace Standards (AS) 8034B, Minimum Performance Standard for Airborne Multipurpose Electronic Displays.
• For HUDs, SAE AS8055, Minimum Performance Standard for Airborne Head Up Display (HUD).
• For liquid crystal displays (LCDs), SAE Aerospace Recommended Practice (ARP) 4256A, Design Objectives for Liquid Crystal Displays for Part 25 (Transport) Aircraft.
Note 1: For LCDs, the quantitative criterion in SAE ARP4256A is not considered a reliable predictor of acceptable specular reflectivity characteristics. Accordingly, this aspect of LCD performance should be specifically assessed via flightcrew evaluation to establish that there are not internal or external reflections that can result in flightcrew distraction or erroneous interpretation of displayed information.
Note 2: With regard to the criteria for malfunction indication in SAE ARP4256A, the FAA has determined that showing the fonts and symbols to be tolerant to the loss of a single column, line, or element is an acceptable alternative to providing a malfunction indication. Proposed designs that do not use fonts and symbols that are tolerant to these faults are acceptable if they meet the criteria in SAE ARP4256A.
Note 3: The applicant should notify the FAA certification engineer if any visual display characteristics do not meet the guidelines in the applicable SAE documents.
Note 4: The most recent revision of the referenced SAE documents should be considered. If there is a conflict between the guidance in an SAE document and this AC, follow the guidance in this AC.
3.2 Visual Display Characteristics.
The visual display characteristics of a flight deck display are directly linked to their optical characteristics. Display defects (for example, element defects or stroke tails) should not impair readability of the display or create erroneous interpretation. In addition to the information elements and features identified in chapter 5 of this AC, and the visual characteristics in SAE ARP4256A, SAE AS8034B, and SAE AS8055, described above, the display should meet the criteria for the following characteristics.
These characteristics are independent of the proposed display technology.
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3.2.1 Physical Display Size.
A display should be large enough to present information in a form that is usable (for example, readable or identifiable) to the flightcrew from the flightcrew station (see related regulation) in all foreseeable conditions, relative to the operational and lighting environment and in accordance with its intended function(s).
3.2.2 Resolution and Line Width.
The resolution and minimum line width should be sufficient to support all the displayed images such that the displayed information is visible and understandable without misinterpretation from the flightcrew station (see related regulation) in all foreseeable conditions, relative to the operational and lighting environment.
3.2.3 Luminance.
Information should be readable over a wide range of ambient illumination under all foreseeable conditions relative to the operating environment, including but not limited to—
• Direct sunlight on the display,
• Sunlight through a front window illuminating white shirts (reflections),
• Sun above the forward horizon and above a cloud deck in a flightcrew member’s eyes, and
• Night and/or dark environment.
3.2.3.1 For low ambient conditions, the display should be dimmable to levels allowing for the flightcrew’s adaptation to the dark, such that outside vision and an acceptable presentation are maintained.
3.2.3.2 Automatic luminance adjustment systems can be employed to decrease pilot workload and increase display life. Operation of these systems should be satisfactory over a wide range of ambient light conditions, including the extreme cases of a forward low sun and a quartering rearward sun shining directly on the display.
3.2.3.2.1 Some manual adjustment should be retained to provide for normal and non-normal operating differences so that the luminance variation is not distracting and does not interfere with the flightcrew’s ability to perform their tasks.
3.2.3.2.2 Displays or layers of displays with uniformly filled areas conveying information such as weather radar imagery should be independently adjustable in luminance from overlaid symbology. The range of luminance control should allow detection of color differences between adjacent small filled areas no larger than 5 milliradians in principal dimension. While at this setting, overlying map symbology, if present, should be discernible.
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3.2.3.3 Display luminance variation within the entire flight deck should be minimized so that displayed symbols, lines, or characters of equal luminance remain uniform under any luminance setting and under all foreseeable operating conditions.
3.2.4 Contrast Ratio.
3.2.4.1 The display’s contrast ratio should be sufficient to ensure that the information is discernible under the whole ambient illumination range from the flightcrew station (see related regulation) under all foreseeable conditions relative to the operating environment.
3.2.4.2 The contrast between all symbols, characters, lines, and their associated backgrounds should be sufficient to preclude confusion or ambiguity of any necessary information.
3.2.5 Chromaticity.
3.2.5.1 The display chromaticity differences, in conjunction with luminance differences, should be sufficient to allow graphic symbols to be discriminated from each other, from their backgrounds (for example, external scene or image background) and background shaded areas, from the flightcrew station (see related regulation), in all foreseeable conditions relative to the lighting environment. Raster or video fields (for example, non-vector graphics such as weather radar) should allow the image to be discriminated from overlaid symbols, and should allow the desired graphic symbols to be displayed. See SAE AS8034B, sections 4.3.3 and 4.3.4, for additional guidance.
3.2.5.2 The display should provide chromaticity stability over the foreseeable conditions relative to the range of operating temperatures, viewing envelope, image dynamics, and dimming range, such that the symbology is understandable and is not misleading, distracting, or confusing.
3.2.6 Gray Scale.
3.2.6.1 The number of shades of gray and the difference between shades of gray that the display can provide should be adequate for all image content and its use, and should accommodate all viewing conditions.
3.2.6.2 The display should provide sufficient gray scale stability over the foreseeable range of operating temperatures, viewing envelope, and dimming range, such that the symbology is understandable and is not misleading, distracting, or confusing.
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3.2.7 Display Response.
The dynamic response of the display should be sufficient to provide discernibility and readability of the displayed information without presenting misleading, distracting, or confusing information. The response time should be sufficient to ensure dynamic stability of colors, line widths, gray scale, and relative positioning of symbols.
Undesirable display artifacts and characteristics, such as smearing of moving images and loss of luminance, should be minimized so that information is still readable and identifiable under all foreseeable conditions, not distracting, and does not lead to misinterpretation of data.
3.2.8 Display Refresh Rate.
The display refresh rate should be sufficient to prevent flicker effects that result in misleading information or difficulty in reading or interpreting information. The display refresh rate should be sufficient to preclude the appearance of unacceptable flicker.
3.2.9 Display Update Rate.
The display update rate should be sufficient to preclude objectionable motion artifacts that could be misleading or distracting.
3.2.10 Display Defects.
Display defects, such as element defects and stroke tails, resulting from hardware and graphical imaging causes should not impair readability of the displays or induce or cause erroneous interpretation. This is covered in more detail in SAE ARP4256A, SAE AS8034B, and SAE AS8055.
3.2.11 Reflections.
Each pilot compartment must be free of glare and reflections that could interfere with the normal duties of a minimum flightcrew. This must be shown in day and night flight tests under non-precipitation conditions (§ 25.773(a)(2)). The criteria and the basic workload functions and factors for a minimum flightcrew are described in appendix D to part 25 and § 25.1523.
3.2.12 Flight Deck Viewing Envelope.
The size of the viewing envelope should provide visibility of the flight deck displays over the flightcrew’s normal range of head motion and should support cross-flight deck viewing if necessary, for example, when it is required that the captain be able to view and use the first officer’s primary flight information. See paragraph 3.3.3 for installation guidance.
3.3 Installation.
3.3.1 Flight deck display equipment and installation designs should be compatible with the overall flight deck design characteristics (such as flight deck size and shape, flightcrew member position, position of windows, external luminance, etc.) as well as the airplane environment (such as temperature, altitude, electromagnetic interference, and vibration).
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3.3.2 RTCA (formerly the Radio Technical Commission for Aeronautics) DO-160G, Environmental Conditions and Test Procedures for Airborne Equipment, and European Organisation for Civil Aviation Electronics (EUROCAE) ED-14G, Environmental Conditions and Test Procedures for Airborne Equipment, provide information that may be used for an acceptable means of qualifying display equipment for use in the airplane environment.
3.3.3 The display unit must be located in the flight deck such that flight, navigation, and powerplant information for use by any pilot is plainly visible to him from his station with the minimum practicable deviation from his normal position and line of vision when he is looking forward along the flight path (§ 25.1321(a)). The primary flight information on the primary display should not be visually obstructed and should remain prominent.
3.3.4 The installation of the display equipment must not adversely affect its readability and the external scene visibility of the flightcrew (see related regulation) under all foreseeable conditions relative to the operating and lighting environment (§ 25.773(a)(1)).
3.3.5 The installation of the display equipment must not cause glare or reflection, either on the displays or on the flight deck windows, that could interfere with the normal duties of the minimum flightcrew (§ 25.773(a)(2)) under all foreseeable conditions.
3.3.6 If the display system design is dependent on cross-flight deck viewing for its use, the installation should take into account the viewing angle limitations of the display units, the size of the displayed information, and the distance of the display from each flightcrew member.
3.3.7 When a display is used to align or overlay symbols with real-world external data (for example, HUD symbols), the display should be installed such that positioning accuracy of these symbols is maintained during all phases of flight. Appendix F of this AC and SAE ARP5288, Transport Category Airplane Head Up Display (HUD) Systems, provide additional details regarding the symbol positioning accuracy for conformal symbology on a HUD.
3.3.8 The display system components should not cause physical harm to the flightcrew under foreseeable conditions relative to the operating environment (for example, turbulence, emergency egress, bird strike, hard landing, and emergency landing).
3.3.9 The installed display must not visually obstruct other controls and instruments or prevent those controls and instruments from performing their intended function (§ 25.1301).
3.3.10 The display system must not be adversely susceptible to electromagnetic interference from other airplane systems (§ 25.1431) under all foreseeable conditions.
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