Table 3 – Field-of-View Data Recommended Field-of-View FOV, Degree from Pilot View Centerline (Note 1) Approx. Distance (inches) From Reference Center Line (Note 1) PFI – Basic T – Electronic or Mechanical 4 (Note 2) 2 (Note 2) Navigation Course Error Data (HSI,
CDI, FD) 15 8 Autopilot and Flight Director Modes 15 8 Navigation Source Annunciation 15 (Note 3) 8 (Note 3) System Warnings and Cautions- Including Failure Annunciation 15 (Note 4) 8 (Note 4) Required Powerplant 35 21 Advisories Annunciations 35 21 Standby Instruments 35 (Note 5) 21 (Note 5) Reversionary Display for PFI 35 21 Note 1. The FOV angles and approximate distance from center reference line, based on a viewing distance of 30 inches from the panel, are defined as acceptable angles and distance to each data source from the center of basic T, or pilot view centerline.
Distances are measured center-to-center of the display in question, and measured horizontally. Vertical placement in the panel can be from just below the basic T to the glare shield.
Note 2. Display PFI as close to the center of reference as possible.
Note 3. The navigation source annunciation should be on or near the affected display and should appear on the same side of the basic T as the affected display. The guidelines for the proximity to the affected display depend on the size, color, and distinguishing characteristics of the source annunciation.
Note 4. Warnings and cautions annunciations should be within 15 degrees. Some annunciations may be acceptable within 35 degrees if they are associated with a unique aural tone or a master warning/caution annunciations that is within 15 degrees and with a pilot evaluation. If an aural tone is used, it should be readily distinguishable from all other cockpit sounds and provide unambiguous information to direct the pilot’s attention to a visual indication of the condition.
Note 5. Install the standby instruments as close as practicable to the PFI.
16.0 Luminance.
16.1 Visual Performance. All displayed information such as symbols, graphics, and alphanumeric characters should be clearly differentiated from one another and legible under all ambient illumination conditions. TSO-C113 and SAE documents Aerospace Standard (AS) 8034, and ARPs 1668B, 4067, and 4256 may be used as guidelines for evaluating the visual performance parameters of the electronic displays relative to viewing, photo colorimetric, luminance characteristics, etc. These conditions range from the night environment to direct sunlight through any window with the operational brightness at the luminance expected at the display’s useful end of-life state. The end-of-life luminance level repr esents the expected value of the display brightness or minimum acceptable output that is established by the manufacturer. The display luminance should sufficiently provide a comfortable level of viewing with rapid adaptation when transitioning from looking outside the cockpit.
16.2 Luminance Level. The luminance level of some displays will gradually diminish over the life of the unit. As part of the continued airworthiness requirements of § 23.1529, consider establishing an operational in-flight evaluation or maintenance evaluation to determine the minimum luminance level appropriate for the type of display, flight deck location, method of format, symbology, color used, etc. Although automatic luminance control compensation is not required, incorporating such a system may decrease pilot workload. Regardless of whether an automatic luminance control is incorporated, provide a manual luminance control that is not adversely affected by failure of any automatic luminance control. Luminance control should not result in some information disappearing while other information remains visible.
17.0 Symbology and Format.
17.1 Symbol Attributes. To minimize confusion or misinterpretation, symbols should be easy to discern, consistent within the cockpit, and learned with minimal training. Symbols should be positioned with sufficient accuracy to avoid interpretation errors or significantly increase interpretation time. Symbols should not have shapes, colors, or other attributes that are ambiguous or could be confused with the meaning of similar symbols. Symbols that represent physical objects (for example, navigational aids and traffic) should not be misleading as to the object’s physical characteristics (including position, size, envelope, and orientation). Electronic displays in the cockpit should use symbology consistent with their intended function. Clearly define and appropriately classify the function of symbology for the pilot. The shape, dynamics, and other symbol characteristics representing the same function on more than one display on the same flight deck should be consistent. Different symbols among different displays for the same functions may be acceptable only if it can be clearly shown that the pilot can quickly and consistently recognize, interpret, and respond correctly without incurring excessive pilot workload. For example, to indicate bank angle on the attitude displays in the cockpit, the type of pointer, ground (fix) or sky (moveable), should be similar for ease of interpretation and to minimize confusion.
17.2 Symbol Standards. Symbols should be based on established industry standards. The symbols in the following SAE documents have been found to be acceptable for compliance to the regulations: SAE ARP 4102/7, ARP 5289, and SAE ARP 5288. For example, the use of flashing letters, such as an “X,” should be consistent. One benefit of symbol standards versus other 36
information formats is the compact encoding of information, which minimizes clutter. However, the symbolic encoding of information should remain simple enough for pilots to learn and recall.
17.3 Clutter. Powerful formats are possible with an electronic display system, but excessive information on a limited display size can result in clutter and reduce the efficiency of the pilot cues. The density of information on the display should be compatible with the pilot's ability to recognize essential information and to minimize misinterpretation. Symbols and markings that are displayed during specific phases of flight may be removed at other times to reduce clutter.
Establish an information prioritization scheme to ensure the clear presentation of essential information. Clutter should be a major consideration during the reversionary or compacted modes.
When combining essential information on a display after another display or unit fails, the display format should not be confusing and the information should still be usable, including unusual attitude. If clutter is anticipated, provide a means to manually remove the clutter (decluttering).
Automatic decluttering, such as during specific phases of flight, or during certain alerts, may also be appropriate.
17.4 Unusual Attitude and Automatic Declutter of the PFD.
a. All primary attitude displays should provide an immediately discernible attitude recognition capability that fosters a safe and effective unusual attitude recovery capability. The display should provide sufficient cues to enable the pilot to maintain full-time attitude awareness and to minimize potential for spatial disorientation. The display should support the initiation of recovery from unusual attitudes within 1 second with a minimum correct response rate of 95 percent. Additional information included on primary flight reference display(s) should not interfere with maintaining attitude awareness, recovering from an unusual attitude, or the interpretation of any PFI.
b. The PFD may require an automatic declutter function during unusual attitudes.
Unusual attitudes generally exceed 70 degrees of bank or +/-30 degrees of pitch, but may vary with airplane performance. The approved configuration (whether basic-T configuration or a new configuration) should be preserved. Basic naviga tion information on the primary navigation display does not need to be decluttered. Flight guidance displayed to assist in unusual attitude recovery should be red and point to the correct direction for proper recovery. SVS information on the display may need to be removed if the attitude source is no longer available. See AC 20-167 for additional guidance on removing SVS information.
Note: Not applicable to aerobatic category airplanes.
17.5 Digital Read-Out Alphanumeric-Only Display of Airspeed and Altitude. Digital read-out presentation of airspeed and altitude should convey to the pilot a quick-glance sense of rate and trend information. For airspeed and altitude, digital read-out alphanumeric displays may not be adequate on the primary display or on the standby instruments, but it is acceptable on a display used as supplementary information. If the applicant proposes a digital read-out alphanumeric display, they should show that the pilot response is equal to or better than the response with analog data (symbology) using a human factors evaluation.
17.6 Round Dial and Moving Scale Display. The display of a round dial, moving pointer with a digital read-out is acceptable. To accommodate a larger operating range on a linear tape, adopt a moving scale display with the present value on a digital readout. Since the moving scale display typically does not provide any inherent visual cue of the relationship of present value to low or high airspeed limits, quick-glance awareness cues may be needed.
17.7 Low-Speed and High-Speed Awareness Cues (Linear Tape Displays).
a. Airspeed displays with fixed pointers and moving scales should provide appropriate low-speed and high-speed awareness cues. Conventional mechanical airspeed indicators for part 23 airplanes include simple green and white speed arcs that, when combined with a moving pointer, provide pilots with adequate low-speed awareness. Airspeed displays incorporating fixed pointers and moving scales require more cues than conventional indicators to compensate for their deficiencies. For part 23 airplanes, prominent green and white arcs provide the pilot with speed cues but not enough to be considered equivalent. Therefore, low-speed awareness cues are necessary for part 23 airplanes.
b. The low-speed awareness cues should include a red arc starting at VSO and extending down toward zero airspeed. During takeoff, the red arc indication of low speed should not be displayed. The applicant may choose an optional yellow band from V S1 down to VSO. The applicant may choose a single conservative stall speed value to account for various weight and flap configurations (reference § 23.1545(a)(4)). For most part 23 airplanes, a fixed value at gross weight and full flaps is acceptable since this has been an adequate safety standard for mechanical gauges. Incorporate a red arc or red barber pole extending from V NE or VMO upward to the end of the airspeed tape.
Note: The red arc below the stall speed is intended for low speed awareness only and is not intended to limit flight operation.
17.7.1 VNE Airplanes. The applicant should show compliance with §§ 23.1311(a)(6) and 23.1545 (paragraphs (a) through (d)), and incorporate the following speed awareness cues for VNE airplanes, as shown in figure 2.
a. Incorporate red band from VSO to 0 (or minimum number).
b. Incorporate red band from VNE to the top of the airspeed tape.
c. Yellow band is optional in the low speed range from VSO to VS1. Use of the yellow band is discouraged (due to clutter) for twin-engine airplanes that incorporate a red and blue line, in accordance with § 23.1545, for one-engine-inoperative speeds.
Red Yellow Green Blank or optional yellow arc Red VNE VNO VFE VS1 VSO Figure 2. Low-Speed and High Speed Awareness for V NE Airplanes 39
D D D 11/17/2011 AC 23.1311-1C
17.7.2 VMO Airplanes. The applicant should show compliance with §§ 23.1311(a)(6) and 23.1545 (paragraphs (a) through (d)), and incorporate the following speed awareness cues for VMO airplanes, as shown in figure 3.
a. Incorporate red band from VSO to 0 (or minimum number).
b. Incorporate red band from VMO to the top of the airspeed tape.
c. The green arc for normal operations is not required, but it may be used if previously approved.
d. The yellow band is optional in the low speed range from VSO to VS1.
Note: On commuter category VMO airplanes, bugs should be provided for setting V1 and V2 This is a blank area represented by a black arc.
Red Black VFE VS1 Blank or optional yellow arc VSO Red Figure 3. Low-Speed and High Speed Awareness for V MO Airplanes 40
17.7.3 Primary Flight Display.
a. Low-speed awareness is an important PFD display function. Stalls remain in the top five causes of fatal accidents for all types of part 23 airplanes, so it makes sense to use the expanded display capability of new part 23 electronic PFDs to address low-speed awareness more effectively.
b. Newer part 23 airplanes are required to also have a stall warning that sounds at 5-10 percent above stall. This was the best that could be afforded with existing technology.
Unfortunately, most stalls occur in VMC and the pilot probably is not looking at the airspeed indicator when the airplane is slowing to a stall.
c. With electronic displays, designers are not constrained to simply reproducing the old round-dial type displays. The displays can have features that were not possible on conventional instruments. Applicants should consider using the display capabilities to direct the pilot’s attention away from looking out the window or fixating on flight or navigation displays such as the FD or HSI. One example the applicants might consider is flashing a large red “STALL” in the center of the PFD and MFD. These should be large enough to direct the pilot’s attention using peripheral vision. Another example is to display an AOA, or AOA-like display, above the airplane symbol (or equivalent) essentially showing the stall margin. Pilots prefer an AOA scheme so they can see their stall margin diminishing and take corrective action based on a trend.
17.8 Linear Tape Altimeter Displays.
a. Linear tape altimeter displays should include enhancements denoting standard 500- and 1,000-foot increments. These displays should convey unambiguously, at a glance, the present altitude. Combining altimeter scale length and markings, therefore, should be enough to allow sufficient resolution for precise manual altitude tracking in level flight. They should also have enough scale length and markings to reinforce the pilot’s sense of altitude. The scale length should also allow sufficient look-ahead room to adequately predict and accomplish level off. Pilot evaluations have shown that, in addition to the appropriate altitude markings commensurate with aircraft performance, an altitude reference bug is recommended to provide acceptable cues.
b. Display a trend indicator unless a Vertical Speed Indicator is located adjacent and to the right of the altimeter. A six-second altitude-trend indicator is typical, but other trend values may be more appropriate depending on the airplane performance and altitude tape scaling.
17.9 Standardization Guide for Integrated Cockpits in Part 23 Airplanes. GAMA Publication No. 12, “Recommended Practices and Guidelines for an Integrated Flightdeck/Cockpit in a 14 CFR part 23 (or equivalent) Certificated Airplane,” is an acceptable means for showing compliance with applicable requirements for electronic displays in part 23 airplanes. AC 23-23, or GAMA Publication No. 12, and this AC should not conflict with one another. GAMA Publication No. 12 provides more specifics in certain areas for standardization for pilot transitions from various cockpits. These specifics are acceptable, but they do not cover all the issues for the installation of 41
electronic displays. One significant benefit of AC 23-23 to standardization between cockpit designs is that it should improve pilot performance (that is, reduce pilot errors, tasks performance times, etc.) when transitioning between different aircraft systems.
17.10 Alternative Formats. Alternative formats or arrangements to those described above should have an adequate human factors evaluation completed to show that pilot response is timely and accurate to at least the level of the existing conventional displays. Human factors criteria should be defined as part of the design process. Because displays are a function of the specific cockpit layout and configuration, human factors evidence needs to be provided during certification.
Specific human factors evaluations and studies that have been performed may support the configuration of displays and their location in the cockpit. Validating these evaluations/studies on each airplane during the certification process is an alternative.
17.11 Integration of Display Parameters. Integration of several display parameters into one common display provides distinct benefits, but it raises some certification issues. New approaches presenting data and commands to the pilot are encouraged. To overcome the issues that may occur as a result of this integration, present the data and commands in a simple format to alleviate any increase in pilot workload. The overall goal is to meet or exceed the existing cockpit performance levels currently in operational use while maintaining pilot workload at acceptable levels.
17.12 Overlays.
a. If overlays are provided, the display format should allow the pilot to overlay weather or other graphics relevant to the flight path on one display without ambiguity. Each new graphic should be evaluated both individually and with allowed combinations of other weather, terrain, and navigation symbology to guard against confusing the pilot or cluttering the screen. When overlaying two or more functions, using the same or similar color to convey different information is not recommended. If the same or similar colors are required, then retain the meaning of the different information. Patterning, bordering, or blanking may be used to clearly depict the different sets of data.
b. If there are multiple depictions, such as inset, inlays, or overlayed depictions, the orientation (for example, heading up, track up, North up, etc.) should be the same for each depiction. This does not apply to other systems where the pilot and copilot may select different presentations of the same information and are used exclusively by that pilot. For more information, see TSO-165.
c. The ability to perform overlays is one of the greatest strengths of an electronic display, but it also creates the potential to produce cluttered or misleading information. Therefore, the number of overlays should not cause the information displayed to become unusable through cluttering or obscuration. Combinations of multiple data presentations should not cause conflicting interpretation of the symbology or icons.
17.13 Scaling. Symbol attributes that use scaling and dynamics should be appropriate for the performance level of the airplane. Conflicting range scaling should not occur. Provide map range.
Always display the range scale for the primary navigation display in the same location on that manufacturer’s product.
18.0 Annunciation.
18.1 General. The electronic display system should provide the pilot with visibly discernible annunciators that will indicate the system operating modes. The visual annunciators should be distinctive under all normal lighting conditions. Under night lighting with the display average brightness at the lowest usable level for prolonged flight, visual annunciators should be usable.
Consistently locate annunciations in a specific area of the electronic display to ensure proper interpretation by the pilot. Using the display selection control position as annunciation is acceptable only under certain conditions. For the flight director, it is acceptable if the control position is appropriately labeled to indicate the function. The control position should be in direct view of the pilot and it should be obvious under all lighting conditions. When a failure occurs or when using reversionary modes, an annunciation of abnormal system status must be provided, in accordance with § 23.1311(a)(7). The display is not to provide any misleading information.
Evaluate annunciations that require pilot action to determine if the required actions could be accomplished in a timely manner without exceptional pilot skill. A failure of any PFI sensor input to the PFD should be appropriately annunciated on the PFD.
18.2 Multiple System Configurations. Where multiple system configurations and more than one sensor input are available for source selection, the switching configuration by annunciation or by selector switch position should be readily visible, readable, and should not be misleading to the pilot using the system. Labels for mode and source selection annunciators should be compatible throughout the cockpit. To ensure the pilot can properly interpret the system status, cautionary annunciation methods should be consistent when numerous interface-switching configurations are possible.
18.3 Alerting Messages. Alerting messages should differentiate between normal and abnormal indications. Abnormal indications should be clear and unmistakable, using techniques such as different shapes, sizes, colors, flashing, boxing, outlining, etc. Provide individual alerts for each function essential for safe operation.
18.4 Visual Crew Alerting and Display Prioritization. Due to the ability to display information from several sources on an integrated display, a prioritization scheme ensures the continuous availability of essential information to the pilot. Prioritization of warnings and caution alerts such as TAWS, Predictive Windshear System (PWS), TCAS, and Reactive Windshear System (RWS) have been established for small airplane applications and are shown in AC 23-18.
Crew alerting information systems require appropriate prioritization of warning, caution, or advisory information. This prioritization includes both visual and aural alerts. Layering the new information over an existing moving map display or an existing weather display, as a result of an automatic pop-up capability, is a common technique. Annunciation of any system level warning, caution, and advisory alert should be compatible with the alert schematic. Prioritize systems information displayed on the MFD to allow ready access to critical information. Less critical 43
information may be less accessible. Provide a means for the pilot to select higher priority information as needed with a single entry on the MFD control panel or keypad.
18.5 Visual Alerts for Warnings. Visual alerts for warnings that require immediate pilot action should be annunciated with an aural warning. Terrain, traffic, and weather are typically displayed in a layered format on the ND, although weather and terrain cannot be displayed at the same time in many current designs. A threat should trigger an automatic pop-up and the appropriate display on the ND, as well as the appropriate aural alert. Subsequent alerts of a higher priority may override the visual display, but the active aural alert should finish before another aural alert of equal or less urgency begins. However, active alerts should be interrupted by alerts from higher urgency levels if the delay to annunciate the higher-priority alert impacts the timely response of the pilot(s). When multiple alerts exist in the same category (for example multiple warning alerts), a means for the pilot to determine the most recent or most urgent should be provided. Other MFD functions, such as checklists, synoptic and expanded systems information, should only be shown when selected by the crew or displayed by phase of flight.
18.6 Supplementary Monitoring of System Status through Independent Sensors.
Electronic displays may present system parameters, such as engine instruments, that can serve as supplementary information to the certified aircraft systems. This information may use sensors that are completely independent from the originally approved sensors. When supplementary information is presented using independent sensors, the presentation cannot interfere or conflict with the primary information. The electronic display should clearly annunciate and/or display any exceedance to the pilot in the appropriate color, following §§ 23.1322 and 23.1549. The AFMS and/or the Pilot Operating Handbook must clearly identify the relationship and procedures associated with those annunciations.
19.0 Lag Time and Data Update.
a. The display of information essential to the safety of flight should be thoroughly responsive and accurate to the operational requirements. Electronic display system delay effects of essential information, including attitude, airspeed, altitude, heading, and specific propulsion parameters, should not degrade the pilot's ability to control the airplane. Any lag introduced by the display system should be consistent with the airplane control task associated with that parameter. Update rates of data on displays should be fast enough so that required symbol motion is free from objectionable lag or stepping.
b. SAE ARPs provide recommended lag times for display of the format and primary flight data, and minimum rates for data updates, to meet symbol motion. A 50-60 Hz refresh rate is typically enough to remove traces of visible flicker on the display. Frequencies above 55 Hz for stroke symbology or non-interlaced raster and 30/60 Hz for interlace raster are generally satisfactory. Some map information may be judged as adequate for enroute navigation displays with update rates of at least 1 Hz, depending on the specific aircraft. Update other critical data, such as attitude, heading, or air data symbology, at a rate of at least 15 Hz, depending on the airplane.
20.0 Controls.
a. Display controls should be clearly visible, labeled, and usable by the pilot, with the least practicable deviation from the normal position and from the line of vision when the pilot is looking forward along the flight path. Controls should have an appropriate amount of tactile feel (for example, detents, friction, stops, or damping, etc.) so they can be changed without undue concentration, which minimizes the potential for inadvertent changes. Design controls for the pilot to be intuitive, that is, so the pilot can rapidly, accurately identify, and select all of the functions of the display control. The controls should be identified easily and located in all lighting conditions, allow differentiation of one control from another, and have feedback through the system appropriate for the function being controlled.
b. Soft controls and cursor control devices development assurance levels should be commensurate with the level of criticality of the airplane system they will control. Redundant methods of controlling the system may lessen the criticality required of the display control. The final display response to control input should be fast enough to prevent undue concentration being required when the pilot sets values or display parameters. The applicant should show by test and/or demonstration in representative motion environment(s) (for example, turbulence) that the display control is acceptable for controlling all functions that the pilot may access during these conditions.
21.0 Test Functions. The electronic display should incorporate a pilot selectable or automatic test mode, such as built in testers, that exercise the system to a depth appropriate to the system design.
Include this function even if the system failure analysis is not dependent on such a mode, or if display test is also a maintenance function. The test mode (or a sub mode) should display warning flags in their proper locations. Exercise alerting and annunciation functions that are necessary to alert the pilot of unsafe conditions. It is acceptable to incorporate the display test with a centralized cockpit light test switch to have the display test function disabled when airborne. The test mode may provide a convenient means to display the software configuration.
22.0 Color Standardization.
22.1 General. Color is considered an enhancement for understanding the display information that leads to performance improvement. Select color to minimize display interpretation errors. A proliferation of color sets can ultimately reduce safety rather than increase it. Using contrast between basic colors provides a better differentiation of display elements than arbitrarily using colors near to each other in the color table. Before defining the color standard for a specific display, establish a consistent color philosophy throughout the display. The FAA does not intend to limit electronic displays to the below listed colors, although these have been shown to work well.
The following section depicts colors found acceptable for compliance with § 23.1322, and other recommended colors as related to their functional meaning for electronic display systems.
Deviations may be approved with acceptable justification. The use of the colors red and yellow for other than warnings and cautions is discouraged. See TSO-C113 and TSO-C63 for additional guidance, 45
22.2 Color for Display Features. Color code display features should be as indicated in the table below:
Table 4 – Color for Display Features Warnings Red Flight envelope and system limits Red Cautions, abnormal sources Amber/Yellow Earth Tan/Brown Scales and associated figures White Engaged modes, flight guidance Green Sky Cyan/Blue ILS deviation pointer Magenta Flight director bar Magenta/Green Pilot selectable references (bugs) Magenta
22.3 Color Sets. One of the following color sets should be used as indicated in the table below:
Table 5 – Color Sets Color Set 1 Color Set 2 Fixed reference symbols, that is, lubber lines White Yellow* 1 Current data, values White Green Armed modes White Cyan Selected data, values Green Cyan Selected heading Magenta**2 Cyan Active route/flight plan Magenta White *1 The extensive use of the color yellow for other than caution/abnormal information is discouraged.
**2 In color set 1, magenta is associated with those analog parameters that constitute "fly to" or "keep centered" type information.