Paragraph
Page
CHAPTER 8. SHOWING COMPLIANCE FOR APPROVAL OF
ELECTRONIC DISPLAY SYSTEMS
46. Compliance Considerations (Test and Compliance) 65
a. General 65
b. Means of Compliance 65
47. – 50. [RESERVED] 67
CHAPTER 9. CONTINUED AIRWORTHINES AND MAINTENANCE
51. Continued Airworthiness and Maintenance 68
a. General 68
b. Design for Maintainability 68
c. Maintenance of Display Characteristics 69
52. – 60. [RESERVED] 69
Appendix Page
LIST OF APPENDICES
1 Primary Flight Information A1-1
1.1 Attitude A1-1
1.2 Continued Function of Primary Flight Information (Including Standby) in Conditions of Unusual Attitudes or in Rapid Maneuvers A1-1
2.1 Airspeed and Altitude A1-2
2.2 Airspeed and Altitude for HUD A1-3
2.3 Low and High Speed Awareness Cues A1-4
3. Vertical Speed A1-6
4. Flight Path Vector or Symbol A1-6
2 Powerplant Displays A2-1
1. General A2-1
2. Design Guidelines A2-2
3 Definitions A3-1 Figure A3-1 Primary Field of View A3-9 Figure A3-2 Display Format A3-11
4 Acronyms Used in This AC A4-1
5 Related Regulations and Documents A5-1 General A5-1
1. Regulations A5-1
2. Advisory Circulars A5-7
3. Technical Standard Orders A5-9
4. Other FAA Documents A5-13
5. ARAC Recommendations A5-13
6. JAA/EASA Documents A5-14
7. Industry Documents A5-14
a. ARINC A5-14
b. EUROCAE A5-15
c. ICAO A5-16
d. RTCA A5-16
e. SAE International (Formerly the Society of Automotive Engineers) A5-18
f. Other Document(s) A5-21
8 CHAPTER 1.
BACKGROUND
1. What is the purpose of this advisory circular (AC)? This 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.
2. Who does this AC apply to?
a. The guidance provided in this document is directed to airplane and avionics manufacturers, modifiers, and operators of transport category airplanes.
b. This material is neither mandatory nor regulatory in nature and does not constitute a regulation. It describes acceptable means, but not the only means, for demonstrating compliance with the applicable regulations. The Federal Aviation Administration (FAA) will consider other methods of demonstrating 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. On the other hand, if 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.
c. This material does not change, create any additional, authorize changes in, or permit deviations from, regulatory requirements.
3. Cancellation. This AC cancels AC 25-11, Transport Category Airplanes Electronic Display Systems, dated 16 July 1987.
4. General. 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,
• 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.
Table 1, below, lists the topics within the guidance of this AC. Table 2, below, lists the topics not within the guidance of this AC.
Table 1 Topics Within the Guidance of This AC
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 (HUD).
Enhanced and Synthetic Vision Systems.
Table 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.
a. 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 25-11A is not intended to replace or conflict with any existing AC. Its purpose is to provide general, highlevel 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 control.
b. 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:
• 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.
c. The ARAC recommendations include adding a new § 25.1302, Installed Systems and Equipment for Use by the Flight Crew and revising the existing § 25.1309, Equipment, Systems, and Installation; § 25.1322, Flightcrew Alerting; and § 25.1333(b), Instrument systems. It is the FAA’s intent that the information in this AC 25-11A 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 § 25.1302, § 25.1309, § 25.1322, and § 25.1333(b).
(1) For information about the ARAC recommendation for § 25.1302 go to http://www.faa.gov/regulations_policies/rulemaking/committees/arac/media/tae/TAE_ HFH_T1.pdf.
(2) For information about the ARAC recommendation for § 25.1309 go to http://www.faa.gov/regulations_policies/rulemaking/committees/arac/media/tae/TAE_S DA_T2.pdf.
(3) For information about the ARAC recommendation for § 25.1322 go to http://www.faa.gov/regulations_policies/rulemaking/committees/arac/media/tae/ TAE_ASH_T4.pdf.
(4) For information about the ARAC recommendation for § 25.1333(b) go to http://www.faa.gov/regulations_policies/rulemaking/committees/arac/ issue_areas/tae/asm/. Section 25.1333(b) is part of the recommendations for “Task 2 - Cockpit Instrument Systems.”
5. Definitions of Terms Used in this AC.
a. For the purposes of this AC, a “display system” includes not only the display hardware and software components but the entire set of avionic devices implemented to display information to the flightcrew. Hardware and software 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.
b. 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.
c. Definitions of technical terms used in this AC can be found in Appendix 3 of this AC.
The acronyms used throughout this document are included in Appendix 4 of this AC. A list of applicable regulations, related guidance, and industry material is included in Appendix 5 of this AC.
6. Background.
a. 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 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.
b. 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
12 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.
7. - 10. [RESERVED]
13 CHAPTER 2.
ELECTRONIC DISPLAY SYSTEM OVERVIEW
11. General. The following paragraphs provide guidance that applies to the overall electronic display system. This chapter, together with Chapters 3 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 1 and 2 of this AC constitutes an overall method of compliance for the approval of an electronic display system.
a. 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) General philosophy of information presentation – for example, is a “quiet, dark” flight deck philosophy used or is some other approach used?
(2) Color philosophy on the electronic displays – the meaning and intended interpretation of different colors – for example, does magenta always represent a constraint?
(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?
(4) Interactivity philosophy - for example, when and why is pilot confirmation of actions requested? When is feedback provided?
(5) Redundancy management philosophy – for example, how are single and multiple display failures accommodated? How are power supply and data bus failures accommodated?
b. Human Performance Considerations. 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, and
• The potential for flightcrew error.
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.
c. 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 ARAC recommendations for adding a new § 25.1302 and the guidance material associated with those recommendations, 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).
d. 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.
12. – 15. [RESERVED]
CHAPTER 3.
ELECTRONIC DISPLAY HARDWARE
16. 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) 8034A, Minimum Performance Standard for Airborne Multipurpose Electronic Displays.
• For head up displays - 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 ARP 4256A, paragraph 4.2.6., equation 5, 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 ARP 4256A, paragraph 3.4, 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 ARP 4256A.
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 AC 25-11A, follow the guidance in AC 25-11A.
a. 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
16 erroneous interpretation. In addition to the information elements and features identified in Chapter 5 of this AC, and the visual characteristics in SAE ARP 4256A, SAE AS 8034A, and SAE AS 8055, described above, the display should meet the criteria for the following characteristics. These characteristics are independent of the proposed display technology.
(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).
(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) 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.
(a) 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.
(b) 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.
1 Some manual adjustment should be retained to provide for normal and nonnormal operating differences so that the luminance variation is not distracting and does not interfere with the flightcrew’s ability to perform their tasks.
17 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.
(c) 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.
(4) Contrast Ratio.
(a) The display’s contrast ratio should be sufficient to ensure that the information is discernable under the whole ambient illumination range from the flightcrew station (see related regulation) under all foreseeable conditions relative to the operating environment.
(b) The contrast between all symbols, characters, lines, and their associated backgrounds should be sufficient to preclude confusion or ambiguity of any necessary information.
(5) Chromaticity.
(a) 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 AS 8034A, sections
4.3.3 and 4.3.4, for additional guidance.
(b) 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.
(6) Gray Scale.
(a) 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.