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• 12/08/2011 AC 20-175
Chapter 3. Additional Guidance for Multifunction Controls
3-1. Multifunction Controls—General. This chapter provides additional guidance that is specific to multifunction controls. The general guidance in chapter 2 still applies to multifunction controls.
a. Unlike a dedicated control, which performs a single function, multifunction controls can control multiple functions. This is enabled primarily through the use of electronic displays as a means for control. This AC covers the following multifunction controls:
Cursor control devices, Touch screens, Menu-based controls, and Voice recognition and voice activated controls Note: This chapter focuses on the first three items, so that “multifunction controls” does not necessarily include voice operated controls, unless specifically noted. However, some of the multifunction controls guidance may still apply to voice operated controls, and/or to electronic displays that are part of the voice-recognition control system.
b. Through the use of electronic displays as a means for controls, multifunction controls can be reconfigured by the system software, which creates opportunities for unique humansystem interface strategies that are currently not possible with traditional dedicated knobs, switches, controls, and physical hardware. As a result, their introduction creates a fundamental change in the design characteristics of the pilot/system interface and the methods pilots use to perform different tasks.
c. Multifunction controls therefore provide unique opportunities and challenges to designers. For example, a large number of traditional controls can require a significant amount of dedicated area in the flight deck. With touch screens, cursor, and menu-based controls the dedicated area can often be reduced to the size of the electronic display. But, this space-saving advantage typically comes at a cost of accessibility and workload, as pilots might have to navigate multiple electronic pages or menu layers to access functions. What once required a simple button push at an easily memorized location might now require a sequence of multiple steps, with many steps needing visual attention.
d. If a multifunction control replaces the function of a conventional control, make a comparison between the two to determine if replacement results in changes in performance and safety, relative to well-understood devices. Show that multifunction controls do not result in unacceptable levels of workload, error rates, speed, and accuracy.
3-2. Multifunction Controls—Inadvertent Operation. Multifunction controls present unique challenges for preventing inadvertent operation. For example, the use of electronic displays as a means for controls might not provide for motion resistance, tactile feedback, or physical protection against operation. Paragraph 2-10c., in this AC, provides multiple methods that have been shown to reduce the likelihood of inadvertent operation of controls. The following paragraphs provide additional methods that might be applicable to multifunction controls.
a. Controls should clearly indicate which areas of the electronic display are active for control functionality. Ensure that pilots can readily identify areas of active control functionality.
Active areas should be sized and organized to permit accurate selection. Moving a finger or cursor to the intended active area should not inadvertently operate other active areas.
b. For controls functions that are accessible from multiple display pages or menus, place controls in a consistent display location, when appropriate. Inconsistent placement can disrupt pilot usage habits and lead to errors.
c. A confirmation step may be provided before activating a function, where appropriate, such as for safety critical functions. For example, when an approach has been activated in a flight management system (FMS), and the pilot changes the selected approach, the system might ask, “Are you sure you want to discontinue the current approach?” Consider the tradeoff between the need for confirmation steps and the increase in pilot workload.
d. Provide a means to reverse an incorrect activation or input, when appropriate. An example means is an “undo” or similar simple reversionary functionality in the system.
3-3. Multifunction Controls —Labeling. Labels for multifunction controls introduce different challenges than for traditional controls. For example, a multifunction control is not necessarily in a fixed location, and may need to be located by navigating through various pages or menus.
Correctly identifying a multifunction control can require additional workload, time, and visual attention compared to traditional, dedicated controls.
a. Indicate a control’s function in a manner that is readily discernable from the current state. For example, a button labeled “Track Up” should not represent the current display orientation of “Heading Up,” but should instead change the display orientation to “Track Up” when selected.
b. Ensure that pop-up text that describes a control’s function does not result in unacceptable distractions, interference, or clutter.
c. If a control activates several different functions based on sequential commands or selections, clearly label each of the functions.
3-4. Multifunction Controls —Cursor Control Devices (CCDs). CCDs provide a means for pilots to indirectly access controls on electronic displays. This is in contrast to touch screens, which allow pilots to directly access controls. Typical CCDs in the flight deck include trackballs, touch pads, and joysticks.
a. A key benefit of CCDs is their convenience; they are typically located on or close to the pilots' natural hand position, and often accompanied by a hand stabilizer or arm rest. This allows for convenient pilot inputs, particularly since hand and arm motion is minimized due to high device gain. However, CCDs can also lead to control errors, particularly when subject to vibration environments. Also CCD inputs are more likely to go unnoticed by other crew members because pilot inputs are typically accomplished with small finger motions on the CCD.
Consider effects on flightcrew coordination in the environment and use conditions of CCDs.
b. Ensure that the cursor symbol is readily discernable from other information, and readily located on the electronic displays. This is particularly important if a cursor symbol is allowed to fade from a display. Some methods to enhance quick location of the cursor are “blooming” or “growing” it to attract the flightcrew’s attention.
c. If more than one cursor is used on a display system, provide a means to distinguish between the cursors.
d. Do not allow the cursor symbol to creep or move without pilot input. Exceptions can include automatic cursor positioning, if it can be shown that it does not result in pilot confusion or unacceptable task completion time.
e. Restrict the cursor symbol from areas of flight critical information, so it does not interfere with legibility. If a cursor symbol is allowed to enter a critical display information field, show that the cursor presence is acceptable.
f. In multi-crew aircraft, most applications will allow more than one flightcrew member to use one cursor. Establish an acceptable method for handling simultaneous “dueling cursors” that is compatible with the overall flight deck philosophy. Establish acceptable methods for other possible scenarios, including the use of two cursors by two pilots.
3-5. Multifunction Controls—Touch Screens. Unlike CCDs, touch screens control systems provide direct access to controls on electronic displays. Because of this, the input device is physically part of the display area. Touch screens utilize different technologies, such as resistive, capacitive, infrared, acoustic, and strain gauge (force-transducer) types. The specific technology affects performance and failures, and is therefore important to consider. For example, not all technologies accommodate the use of gloves.
a. Touch screens can be susceptible to control errors in part because the electronic displays (on which pilot inputs occur) typically are smooth and flat. Their surface offers little tactile feedback for determining finger position and motion, which can result in a greater need for visual attention. Therefore, consider integrating an associated support for stabilizing the pilot's hand, and for providing a reference point when positioning fingers, if appropriate. Ensure 19
that touch screens do not result in unacceptable levels of workload, error rates, speed, and accuracy.
b. Ensure that touch screens resist scratching, hazing, or other damage that can occur through normal use. Demonstrate that the system will continue to provide acceptable performance after long-term use and exposure to skin oils, perspiration, environmental elements
(e.g., sun), impacts (e.g., clipboard), chemical cleaners that might be used in the flight deck, and any liquids that might be brought onboard by flightcrew members (e.g., coffee).
c. If a touch screen’s calibration can drift or degrade, provide touch screen calibration procedures and other maintenance-related items to ensure proper calibration and operation.
Include these procedures in the instructions for continued airworthiness, per § 2X.1529.
d. The location of the pilot’s finger touch, as sensed by the touch screen, should be predictable and obvious.
3-6. Multifunction Controls—Menus and Navigation. In menus, the layering of information should not hinder the pilot in identifying the location of the desired control. Location and accessibility are not only related to the physical location of the control function. They also include consideration of where the control functions are located within various menu layers, and how the pilot navigates through those layers to access functions.
a. For menu-based controls, ensure that the number and complexity of steps required to access and utilize a control is appropriate to the intended use of the control (e.g., frequently used controls and emergency controls should be available at top-level menus). The number of submenus should be designed to ensure timely access to the desired option without over-reliance on memorization of the menu structure.
b. Cockpit controls must be located and identified to provide convenient operation and to prevent confusion, per § 2X.777(a). Layer information on menus or hidden pages so it does not hinder the flightcrew in identifying the location of the desired control.
c. Fit top-level control menu pages (e.g., primary or “home” page) entirely on the display
(i.e., do not require scrolling).
d. Make top-level control menus readily accessible. This is typically accomplished by continuously displaying the menu or menu access control in a fixed location (e.g., “home” page).
e. Provide feedback from page navigation that is an unambiguous indication of the current location.
3-7. Multifunction Controls—Voice Recognition and Voice Activated. Voice recognition and voice activated control systems in aircraft pose special challenges. Recognition accuracy of voice commands is less than perfect, and its performance is affected by pilot characteristics as well as the ambient noise environment. This section provides basic guidance and human factors considerations for voice recognition and voice activated controls, but it does not 20
comprehensively address either.
a. Ensure that voice recognition and voice activated control systems consistently and accurately recognize and properly input verbal commands from pilots under expected flight and ambient noise conditions (see chapter 2, paragraph 2-2.k). Typical background aircraft noise, crew and passenger conversations, radio communication traffic, and sound from other sources should not impede the system.
b. Provide a simple and readily apparent means to deactivate the voice recognition or voice activated system.
c. Ensure that voice recognition and voice activated control systems do not interfere with normal pilot communication functions (e.g., air traffic control and other aircraft).
Appendix A Appendix A. Related Documents and Acronyms
1. References.
a. AC 25-11A, Electronic Flight Deck Displays.
b. AC 23-23, Standardization Guide for Integrated Cockpits in Part 23 Airplanes.
c. AC 23.1311-1B, Installation of Electronic Display in Part 23 Airplanes.
d. AC 27-1, Certification of Normal Category Rotorcraft.
e. AC 29-1, Certification of Transport Category Rotorcraft.
f. RTCA/DO-275, Minimum Operational Performance Standards for Integrated Night Vision Imaging System Equipment, October 2001.
g. SAE ARP4102, Flight Deck Panels, Controls, and Display, July 2007.
h. SAE ARP4102/7, Electronic Display, July 2007.
i. SAE ARP4105B, Abbreviations and Acronyms for Use on the Flight Deck, reaffirmed June 2004.
j. FAA Policy ANM-01-03A, Factors to Consider when Reviewing an Applicant’s Proposed Human Factors Methods of Compliance for Flight Deck Certification, in Part 25 Airplanes.
k. Human Factors Design Standard for Acquisition of Commercial-Off-The-Shelf Subsystems, Non-Developmental Items, and Developmental Systems. eds: V. Ahlstrom & K. Longo. May 2003. FAA Technical Center: Atlantic City, NJ. DOT/FAA/CT-03/05 HF-STD-001. http://www.hf.faa.gov/hfds.htm
l. International Civil Aviation Organization, Doc 8400, ICAO Abbreviations and Codes, Sixth Edition, 2004.
m. MIL-STD-1472F, Department of Defense Design Criteria Standard: Human Engineering, August 23, 1999.
2. How to Get Referenced Documents. You can get copies of FAA Advisory Circulars from our Regulatory and Guidance library (RGL) at www.airweb.faa.gov/rgl. On the RGL website, select “Advisory Circulars,” then select “By Number.” You can obtain a copy of Modification and Replacement Parts Association’s (MARPA) guidance on continued operational safety (COS) at www.pmaparts.org/gvt/COSGuidance.pdf.
A 1--
Appendix A
3. Acronyms.
AC Advisory circular AGL Above ground level ARP Aerospace Recommended Practice ASTC Amended supplemental type certificate ATC Amended type certificate CCD Curser control device CFR Code of Federal Regulations COS Continued operational safety DO Document DOT Department of Transportation EFB Electronic flight bag FAA Federal Aviation Administration FMS Flight management system ICAO International Civil Aviation Organization MARPA Modification and Replacement Parts Association MG Minimum guidance NVG Night vision goggles NVIS Night vision imaging system PED Portable electronic device RGL Regulatory Guidance Library RTCA RTCA Inc.
RTCA/DO RTCA Inc. Document SAE SAE International STBY Standby STC Supplemental type certificate TC Type certificate A-2
Appendix B Appendix B. Control-Function Matrix
1. Introduction.
a. This appendix provides a brief description of a “control-function matrix”. It is not required for compliance, but can be helpful as a method for development, and for sharing data with the FAA.
b. A control-function matrix primarily maps control devices (e.g., knob) to control functions (e.g., change radio frequency). The matrix also provides for an organization of controls-related attributes, such as those addressed in this AC. It is a tool sometimes used by applicants to organize their design and compliance effort.
2. Table B-1. Table B-1 provides an example template of a control-function matrix.
The columns in table B-1 are described as follows:
a. Control: List each control separately in the table. Include traditional dedicated controls (e.g., knobs) and multifunction controls (e.g., software menus, touch-screen buttons) in the list.
b. Function Description Section: Group information that describes a function performed by a control in the matrix. In the table B-1 example, the function, criticality, frequency of use, and operational conditions are addressed.
(1) Function: Each function provided by a control is listed next to the name of the control. If a control provides multiple functions, list each function on a separate row, since the supplemental information may be quite different for each function.
(2) Criticality for Safety: This column provides relevant information about the criticality of a function from a system safety analysis. Criticality information can be helpful when considering implications associated with the possible inadvertent operation of a control (e.g., critical controls may need additional degrees of protection against inadvertent operation).
(3) Expected Frequency of Use: This column describes the frequency with which a function will be activated, deactivated, or manipulated. This information describes the function provided by the control. Frequency information can be helpful when considering the level of familiarity the pilot can be expected to have with a control, relative to its accessibility and complexity of operation (e.g., frequently used controls that are at the edge of a pilot’s reach envelope may not be compliant with 14 CFR 2x.777).
(4) Operational and Use Conditions: This column describes any operational use conditions that can impact the use of the control for that particular function. Operational and use conditions include those described in chapter 2, paragraph 2-2 of this AC, as well as flight phase. The information therefore establishes context in which the controls will be operated (e.g., functions that are regularly performed during final approach and B-1
Appendix B landing might need to employ a very simple method of operation to be compliant with 14 CFR 2x.771) and the acceptability of other features of the control’s design.
c. Design Description Section: Group information that describes the physical design of the control and its associated elements into the matrix. The table B-1 example groups information about methods of operation, labels, protection against inadvertent actuation, feedback from control actuation, and location of the control when installed.
(1) Method of Operation: Describe the method of operation for a function. A control that provides multiple functions could have the same method of operation for different functions, or it could have different methods of operation for different functions.
If a method of operation is difficult to describe in this matrix, it might also be difficult to perform for the pilot.
(2) Label: State the label associated with a function and method of operation.
This information is useful to ensure that all functions are labeled and there is no inappropriate use of the same label for different functions, or different labels for identical functions. If no label is provided, make an assessment to ensure that the control is “obvious.”
(3) Protection from Inadvertent Operation: This column captures descriptions of any design features that will prevent or reduce the likelihood of inadvertent operation of a function. This information might support compliance with 14 CFR 2x.777, requiring protection against inadvertent operation of controls.
(4) Feedback: This column captures information regarding feedback to the pilot during or following operation of a control.
(5) Location/Association: This column captures a description of the location of the control when installed. This information can be useful for understanding, for example, functional groupings and control-displays association.
d. Other Information Section: There may be several additional categories of information that are relevant to a function, the design of a control, factors that influenced the design decision process for the control, or the process of showing compliance. The table B-1 example uses a listing of related controls for each function, and a picture of the control.
B-2
Appendix B Table B-1. Example Template for Control-Function Matrix Control Function Description Design Description Other Information Function Criticality for Safety Expected Frequency of Use Operational and Use Conditions Method of Operation Label Protection from Inadvertent Operation Feedback Location/ Association Related Controls Picture(s) of Control [Name of Control, or Reference # in Diagram] [Name and Brief Description of Function #1] [e.g., Catastrophic Function, OR Major Function, OR Minor Function] [e.g., Multiple times per flight , OR Once per flight , OR Occasional use, OR Rarely used] [e.g., Control will be used during high workload phase of flight, in cold weather, in high vibration conditions] [Description of pilot actions required to perform Function #1] [Text of Label;
or “None”] [Description of design features that prevent inadvertent operation, or “None”] [Description of visual, aural, tactile, or other cues provided to indicate successful or unsuccessful operation of the control] [Position of control relative to the pilot upon installation]
(e.g., using a flight deck Zone reference) [List of Names or Reference #’s for other Controls associated with Function #1] [Name and Brief Description of Function #2] [e.g., Catastrophic Function, OR Major Function, OR Minor Function] [e.g., Multiple times per flight , OR Once per flight , OR Occasional use, OR Rarely used] [e.g., Control will be used during high workload phase of flight, in cold weather, in high vibration conditions] [Description of pilot actions required to perform Function #2] [Text of Label;
or “None”] [Description of design features that prevent inadvertent operation, or “None”] [Description of visual, aural, tactile, or other cues provided to indicate successful or unsuccessful operation of the control] [Position of control relative to the pilot upon installation]
(e.g., using a flight deck Zone reference) [List of Names or Reference #’s for other Controls associated with Function #2] B-3
Appendix C Appendix C. Regulations Table C-1 provides a quick reference to some 14 CFR regulations that address controls.
While many other regulations also apply to flight deck controls, as determined by the applicant’s regulatory basis, this AC focuses on the regulations in table C-1 because they are strongly related to human factors, and have often been subject to interpretation during aircraft certification projects. Table C-2 lists additional regulations that were cited in the AC.
Table C-1. Quick Reference to Regulations for Controls Related to Human Factors.
Key Aspect of Regulation, From a Human Factors Perspective (In some cases, wording may be paraphrased for clarity.
Consult regulations for exact wording.)
14 CFR Regulations Each control must operate with the ease, smoothness, and positiveness appropriate to its function.
23.671(a), 25.671(a), 27.671(a),
29.671(a) Controls must be located {part 23 only: arranged, and identified} to provide for convenience in operation.
23.671(b), 23.777(a), 25.777(a),
27.777(a), 29.777(a) Controls must be located {part 23 only: arranged, and identified} to prevent the possibility of confusion and subsequent inadvertent operation {part 29 only: from either pilot seat}.
23.671(b), 29.771(b), 23.777(a),
25.777(a), 27.777(a), 29.777(a) The pilot compartment must allow the pilot to perform his duties without unreasonable concentration or fatigue.
23.771(a), 25.771(a), 27.771(a),
29.771(a) The aircraft must be controllable with equal safety from either pilot seat.
25.771(c), 27.771(b), 29.771(b) Vibration and noise characteristics of cockpit equipment may not interfere with safe operation of the aircraft.
25.771(e), 27.771(c), 29.771(c) Controls must be identified (except where the function is obvious).
23.777(a) Controls must be located and arranged, with respect to the pilot seat, to provide full and unrestricted movement of each control without interference.
23.777(b), 25.777(c), 27.777(b),
29.777(b) A control must be of a kind and design appropriate to its intended function.
23.1301(a), 25.1301(a)(1),
27.1301(a), 29.1301(a) Controls must function properly when installed. 23.1301(d), 25.1301(a)(4),
27.1301(d), 29.1301(d) For alerting lights, installed in the cockpit, the color red must be used for warnings and the color amber for cautions.
23.1322, 27.1322, 29.1322 Use of the colors red, amber, and yellow on the flight 25.1322(e)(1), (f) C-1
Appendix C deck for functions other than flightcrew alerting must be limited and must not adversely affect flightcrew alerting.
Instrument lights must make each instrument and control easily readable and discernable.
23.1381(a) Instrument lights must make each instrument, switch, and other device, easily readable.
25.1381(a)(1), 27.1381(a),
29.1381(a) Instrument lights must be installed so that no objectionable reflections are visible to the pilot.
25.1381(a)(2)(ii), 27.1381(b)2,
29.1381(b)2 The minimum flightcrew must be able to access and easily operate controls required for safe operation.
23.1523, 25.1523, 27.1523,
29.1523 A cockpit control must be plainly marked as to its function and method of operation.
23.1555(a), 25.1555(a),
27.1555(a), 29.1555(a) Table C-2. Additional Cited Regulations General Topic 14 CFR Regulations Cockpit control knob shape. 25.781, 23.781 Instructions for continued airworthiness. 23. 1529, 25.1529. 27.1529,
29.1529 C-2