General

·        Flight deck controls must be installed to allow accomplishment of all the tasks required to safely perform the equipment's intended function, and information must be provided to the flightcrew that is necessary to accomplish the defined tasks. [14 CFR 25.1302(a)]

        See also: Chapter 8 Intended Function

·        Each detail of each control system must be designed and installed to prevent jamming, chafing, and interference from cargo, passengers, loose objects, or the freezing of moisture. [14 CFR 23.685(a), 25.685(a)]

See also: 14 CFR 27.685(a) and 29.685(a) which are worded slightly differently.

·        Flight deck controls and information intended for the flightcrew’s use must: [14 CFR 25.1302 (b)]

        (1)   Be provided in a clear and unambiguous manner, at a resolution and precision appropriate to the task.

        (2)   Be accessible and usable by the flightcrew in a manner consistent with the urgency, frequency, and duration of their tasks, and

        (3)   Enable flightcrew awareness, if awareness is required for safe operation, of the effects on the airplane or systems resulting from flightcrew actions.

·        For each of these requirements, the proposed means of compliance should include consideration of the following control characteristics for each control individually and in relation to other controls: [AC 25.1302-1, 5-4.b(2)]

        (a)   Physical location of the control.

        (b)   Physical characteristics of the control (e.g., shape, dimensions, surface texture, range of motion, color).

        (c)   Equipment or system(s) that the control directly affects.

        (d)   How the control is labeled.

        (e)   Available control settings.

        (f)    Effect of each possible actuation or setting, as a function of initial control setting or other conditions.

        (g)   Whether there are other controls that can produce the same effect (or affect the same target parameter)and conditions under which this will happen.

        (h)   Location and nature of control actuation feedback.

·        The flight guidance system functions, controls, indications, and alerts must be designed to minimize flightcrew errors and confusion concerning the behavior and operation of the flight guidance system. Means must be provided to indicate the current mode of operation, including any armed modes, transitions, and reversions. Selector switch position is not an acceptable means of indication. The controls and indications must be grouped and presented in a logical and consistent manner. The indications must be visible to each pilot under all expected lighting conditions. [14 CFR 25.1329(i)]

See also: 14 CFR 23.1329(h), 27.1329(f), 29.1329(f) which are worded slightly differently.

·        Operations that occur with high frequency or in the terminal area should be executable with a minimum number of control operations. [TSO-C165/RTCA DO-257A, 2.1.5]

        See also: TSO-C146c/RTCA DO-229, 2.2.1.1.3 and RTCA DO-256, 2.1.1 which are worded slightly differently.

·        The number of operations may be minimized through the use of dedicated controls, anticipation of pilot requirements and the use of quick-access menus designed to facilitate rapid selection of required navigation functions, such as direct flight to a waypoint and returning to the final approach course after a missed approach. [TSO-C146c/RTCA DO-229D, 2.2.1.1.3]

·        Controls, displays and annunciations must not result in misleading information, pilot confusion or unacceptable workload due to possible inconsistencies from differences in the equipment (e.g., different flight plans making one unit go into approach mode while the other does not). [AC 20-138C, 13-4.b(4)]

·        Controls should be designed to maximize usability, minimize flight crew workload, and reduce pilot errors. [TSO-C165/RTCA DO-257A, 2.1.5]

·        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. [AC 23.1311-1C, 20.0.a]

·        Identical powerplant controls for each engine must be located to prevent confusion as to the engines they control. [14 CFR 23.777(e), 25.777(d)]

·        The evaluation of these controls should include a thorough examination of the control location and mechanization. The physical arrangement of the controls on multi-engine should be consistent with the physical location of the engines on the airplane as far as left to right sequence. They should also be examined in conjunction with their associated displays and warning indications when failures occur. Every effort should be made to provide clear unmistakable indications to prevent these situations from occurring. Also, marking and lighting of the engine controls needs to be clear and distinct to prevent any confusion to the pilot. Compliance testing identified in the human factors certification plans should begin with analysis of initial engineering studies and continue through mock-up, simulator and aircraft ground/flight test evaluations. [PS-ACE100-2001-004, Appendix A]

·        The following are examples of flight deck control issues which should be avoided: [AC 27-1B, AC 27.777; AC 29-2C, AC 29.777)

        (i)    Collective control blocking the lateral movement of a pilot’s leg, which in turn restricts the left lateral cyclic displacement.

        (ii)   Seat or seat cushion impeding the aft cyclic movement.

        (iii)  Inadequate space for large feet equipped with large flight boots.

        (iv)  Control/seat relationship which requires unusual pilot contortions at extreme control displacements.

        (v)   Control/seat relationship or control system geometry which will not permit adequate mechanical advantage with unboosted controls or in a boost OFF situation.

        (vi)  Addition of control panels or equipment to instrument panels or consoles which restrict full control throw.

        (vii) Brake pedal geometry which results in inadvertent brake application upon displacement of the directional controls.

        (viii) Controls for accessories or equipment which require a two-handed operation.

        (ix)  Emergency external cargo release controls which cannot be activated without releasing the primary flight controls.

        (x)   Essential controls which cannot be actuated during emergency conditions with the shoulder harness locked.

        (xi)  Throttle controls which can be inadvertently moved through idle to the cutoff position.

        (xii) Switches, buttons, or other controls which can be inadvertently activated during routine cockpit activity including cockpit entry.

        (xiii) Failure to account for operation with the pilot wearing bulky winter clothing.

        (xiv) Aft cyclic movement limited by the pilot’s body with a fore and aft adjustable seat in the full forward position.

Identifiable and Predictable Controls

·        Pilots must be able to identify and select the current function of the control with speed and accuracy appropriate to the task, per § 2X.777(a). Make the function and method of operation of a control readily apparent (i.e., predictable and obvious), so that little or no familiarization is needed. Show that the intended pilot population can rapidly, accurately and consistently identify and execute all control functions, assuming qualified and trained pilots. [AC 20-175, 2-7.a]

See also: AC 25.1302-1, 5-4.c(1)(a)

·        The applicant should evaluate consequences of control activation to show that the consequences are predictable and obvious to each flight crewmember. Such an assessment would include evaluation of the control of multiple displays with a single device and evaluation of shared display areas that flightcrew members access with individual controls. The use of a single control should also be evaluated. [AC 25.1302-1, 5-4.c(1)(b)]

        See also: AMC 25.1302, 5.3.3.a

·        Controls can be made distinguishable or predictable by differences in attributes such as form, color, location, and labeling. For example, buttons, which are pushed, should be readily discernable from knobs, which are rotated. Control shapes that are easily determined with tactile senses can improve ease of operation, particularly during periods when pilot tasks require significant visual attention. [AC 20-175, 2-7.b]

See also: AC 25.1302-1, 5-4.c(1)(c)

·        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. [AC 23.1311-1C, 20.0.a]

·        Color coding as a sole distinguishing feature is usually not sufficient. This applies to physical controls as well as to controls that are part of an interactive graphical user interface. [AC 25.1302-1, 5-4.c(1)(d)]

·        The labeling design should avoid hidden functions such as clicking on empty space on a display to make something happen. [AC 25.1302-1, 5-4.c(2)(c)]

See also: AMC 25.1302, 5.3.3.b

Design Philosophy

·        If you are an applicant, document and follow a design philosophy for controls, which supports the intended functions (14 CFR 2x.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 controls features, such as labeling, feedback, automated behavior, and error recovery. Also include a high level description of human performance considerations, such as flightcrew workload, error potential, and expected training requirements. [AC 20-175, 2-1.a]

        See also: Chapter 8 Intended Function

·        Apply a particular design philosophy consistently throughout the flight deck to the greatest extent practicable. [AC 20-175, 2-1.b]

·        If color is used for coding task-essential information, use at least one other distinctive coding parameter (e.g., size, shape, label). Whenever possible, color coding should be consistent across all controls and displays. Consider the effect of flight deck lighting on the appearance of the label, and the use of colors throughout the flight deck (i.e., color philosophy). [AC 20-175, 2-7.c]

        See also: Chapter 3.1 Electronic Display Information Elements and Features: General; Chapter 3.7 Color; Chapter 7 Design Philosophy

Environment and Use Conditions

·        Consider a variety of environments, use conditions, and other factors that can impact flightcrew interaction with controls during aircraft operations that can be reasonably expected in service, including: [AC 20-175, 2-2.a]

        -   Appropriate representation of pilot population;

        -   Bright and dark lighting conditions;

        -   Use of gloves;

        -   Turbulence and other vibrations;

        -   Interruptions and delays in tasks;

        -   Objects that may physically interfere with the motion of a control;

        -   Incapacitation of one pilot (multi-crew aircraft);

        -   Use of the non-dominant hand; and

        -   Excessive ambient noise.

·        Since all possible environment and use conditions cannot be specifically addressed, develop a representative set that includes nominal and worst cases. These cases should cover the full environment in which the system is assumed to operate, given its intended function. This includes operating in normal, non-normal, and emergency conditions. The following paragraphs describe the above list of environment and use conditions in more detail. [AC 20-175, 2-2.b]

        See also: Chapter 8 Intended Function

·        Some control operations involve multiple steps such that interruptions and delays might affect successful completion. For example, pilots might forget to complete a task they started (e.g., air traffic control calls), or they might not understand how the system behavior accommodates

        unfinished tasks (e.g., data entry timeouts). In environment and use conditions, include interruptions and delays during pilot-system interaction tasks to understand if the controls’ behavior results in any safety-critical consequences. [AC 20-175, 2-2.h]

·        Pilots might wear gloves during operations, such as in cold weather. Design assumptions regarding skin contact (e.g., tactile feedback, system capacitive sensing), finger size (e.g., button spacing), and other finger characteristics alone might not adequately cover situations in which pilots wear gloves. Therefore, include gloved pilot operations in environment and use conditions. In cases where controls cannot be operated with gloves, clearly describe any limitations or methods for determining limitations, in the aircraft flight manual or flight manual supplement, as appropriate. [AC 20-175, 2-2.e]

See also: AC 25.1302-1, 5-4.e(1)(b) and AMC 25.1302, 5.3.5.a which are worded slightly differently.

·        Ensure that controls are operable during vibrations. Vibrations affect not only the ability of pilots to intentionally activate a control, but also can affect inadvertent activation and awareness of activation. Vibrations can be caused by turbulence, propulsion systems, or other means. [AC 20-175, 2-2.f(1)]

See also: AC 25.1302-1, 5-4.e(1)(a) and AMC 25.1302, 5.3.5.a which is worded slightly differently.

·        Title 14 CFR 25.771(e), 27.771(c), and 29.771(c) require that vibration and noise characteristics of cockpit equipment not interfere with the safe operation of the aircraft. Theoretical analysis alone is insufficient for demonstrating compliance, but it can be complementary. Therefore, also show through other means, such as test or demonstration, that the control is acceptable over a range of vibration environments for the intended aircraft and operations. Multifunction controls tend to be particularly susceptible to vibrations (see chapter 3). For functions with multiple means of control access, ensure that at least one of the controls is operable during vibrations. [AC 20-175, 2-2.f(2)]

Control Use in Noise

·        Controls should be operable during conditions of excessively high ambient noise (e.g., from engines, airflow). Make noise conditions represent what can reasonably be expected for the intended aircraft and operation. [AC 20-175, 2-2.k]

·        When aural feedback is a control feature, it may be necessary to incorporate other sensory feedback as well (e.g., visual, tactile). [AC 20-175, 2-2.k]

Control Illumination/Visibility

·        Controls should be operable under foreseeable lighting conditions. [AC 20-175, 2-2.d(1)]

·        Controls should be designed for nighttime usability (e.g., illuminated). [TSO-C165/RTCA DO-257A, 2.1.5.1]

        Note:  Control illumination may be achieved by either illuminating the control itself or providing flight deck (external) illumination. This will need to be evaluated on an installation specific basis. [TSO-C165/RTCA DO-257A, 2.1.5.1]

·        Lighting of one control should not interfere with viewing and identification of adjacent controls. [PS-ACE100-2001-004, Appendix A]

·        The applicant should show the controls required to regain airplane or system control and to continue operating the airplane in a safe manner are identifiable and usable in all environmental conditions, to include dense smoke in the flightdeck and severe vibrations. An example of the latter condition would be after a fan blade loss. [AC 25.1302-1, 5-4.e(1)(d)]

        See also: AMC 25.1302, 5.3.5.a which is worded slightly differently.

Controls Lighting

·        For controls with visual markings that are intended for use in low-light conditions, the markings must be lighted in some way that allows them to be easily read, for compliance with § 2X.1555(a) and § 2X.1381(a). [AC 20-175, 2-9.a]

·        Ensure that lighting of controls is consistent with flightcrew alerting such as warning, caution, and advisory lights (§ 2X.1322). [AC 20-175, 2-9.b]

·        For low-light conditions, make lighted controls dimmable to brightness levels commensurate with other flight deck instrument lighting. This allows for the flightcrew’s adaptation to the dark, so controls are legible, and outside vision is maintained. [AC 20-175, 2-9.c]

·        Ensure that lighting of controls from an internal source is not dimmable to brightness levels so low that the controls appear inactive. [AC 20-175, 2-9.d]

·        Ensure that lighting of controls from an internal source does not produce light leaks, bright spots, or reflections from the windshield that can interfere with pilot vision or performance. [AC 20-175, 2-9.e]

·        Automatic adjustment of lighted controls may be employed. Consider preference differences in multi-crew operations. [AC 20-175, 2-9.f]

·        Ensure that lighted controls intended for operation in a night vision imaging system (NVIS) lighting-modified cockpit meets AC 20-175, 2-9.a through 2-9.e, and are compatible with night vision goggles (NVG). [AC 20-175, 2-9.g]

        Note: NVIS lighting must allow color transmission to meet aircraft certification regulations (e.g., §§ 2X.1381, 2X.1555). For controls that do not need color discrimination, NVIS A lighting can be used. For controls where color discrimination is needed, then NVIS lighting must (§ 2X.1555) allow the pilot to easily discern the required colors (typically accomplished using NVIS white). Make perceived color for reds, yellows (or ambers), and greens the same across the cockpit. [AC 20-175, 2-9.g]

·        Electronic displays are required to have adequate contrast and brightness to be legible in all ambient lighting environments from bright sunlight to total darkness. The lighting controls must also have an adequate range of adjustment to accommodate these conditions. This requirement is intended to provide readable displays without increasing pilot workload (for example, trying to shield the display to read it). [PS-ACE100-2001-004, Appendix A

Control Labels 

See also: Chapter 3.2 Labels

·        Each cockpit control, other than primary flight controls and controls whose function is obvious, must be plainly marked as to its function and method of operation. [14 CFR 25.1555(a), 27.1555(a), 29.1555(a)]

        See also: 14 CFR 23.1555(a) which is worded slightly differently.

·        Each secondary control must be suitably marked. [14 CFR 23.1555(b)]

·        Labels shall be used to identify the functions of all controls used to manipulate the information content and operating characteristics of the display. [TSO-C165/RTCA DO-257A, 2.1.5.1]

        Note: This requirement applies to standard mechanical controls (e.g., buttons, knobs, etc.). [TSO-C165/RTCA DO-257A, 2.1.5.1]

        See also: RTCA DO-256, 2.1.3.5 which is worded slightly differently.

·        Controls whose functions are not obvious should be marked or identified so that a flightcrew member with little or no familiarity with the airplane is able to rapidly, accurately, and consistently identify their functions. [AC 25-11A, 31.c(2)]

·        If a control performs more than one function the labels should include all intended functions, unless the function of the control is obvious. [AC 25-11A, 31.c(2)(b)]

        See also: Chapter 8 Intended Function

·        Labels of graphical controls accessed via a cursor control device should be included on the graphical display. [AC 25-11A, 31.c(2)(b)]

·        On multi-function displays, a label should be used to indicate the active function(s), unless its function is obvious. When the function is no longer active or being displayed, the label should be removed unless another means of showing availability of that function is used. [AC 25-11A, 31.c(2)(d)]

·        Terminology for labeling should describe the function of the control in meaningful terms. Terms should be consistent with those on the display of the function or mode selected and spelled out whenever possible. [TSO-C146c/RTCA DO-229D, 2.2.1.1.1.2]

·        Labels are the most common means used to identify and describe controls and other devices in the flight deck. They can be full text (e.g., “Standby”), abbreviated text (e.g., “STBY”), acronyms (e.g., “AGL” for “Above Ground Level”), as well as icons (e.g., for “On/Off”). [AC 20-175, 2-8.a]

        Note: While a limited number of control functions might have icons associated with them that pilots would likely know, most functions have no universally accepted icons. [AC 20-175, 2-8.a]

·        Control labels must be visible, legible, and understandable for the population of pilots that will use the controls, per § 2X.1555(a). [AC 20-175, 2-8.b]

·        Unless the control function and method of operation are obvious or indicated through other means (e.g., form, location), the control labeling scheme should clearly and unambiguously convey: [AC 20-175, 2-8.c]

        -   The current function performed by each control,

        -   The method for actuating the control when performing the current function.

        See also: AC 25.1302-1, 5-4.c(2)(a) which is worded slightly differently.

·        Labels and other information related to a control’s function and method of operation should be readable over a wide range of ambient illumination, including, but not limited to: [AC 20-175, 2-2.d]

        -   Direct sunlight on the controls;

        -   Indirect sunlight through a front window illuminating white clothing (reflections);

        -   Sun above the forward horizon and above a cloud deck in a flightcrew member’s eyes; and

        -   Night and/or dark environment.

        Consider the above conditions when evaluating controls, and show that the controls are acceptable. Compensating factors such as tactile characteristics, can also be included as part of the environment and use conditions. Special consideration is needed for controls whose function is affected by illuminated information (see paragraph 2-9 in this chapter), such as lighted switches and soft keys on displays. [AC 20-175, 2-2.d]

·        If a control can be used for multiple functions, the current function shall be indicated either on the display or on the control. [TSO-C165/RTCA DO-257A, 2.1.5.1]

        See also: AMC 25.1302, 5.3.3; TSO-C146c/RTCA DO-229D, 2.2.1.1.4.1; RTCA DO-256, 3.2.1.2.2 which are worded slightly differently.

·        Size control labels to be easily legible from the pilot’s normally seated position. [AC 20-175, 2-8.d]

·        Multi-function controls should be labeled such that the pilot is able to [AC 25-11A, 41.a]:

        -- Rapidly, accurately, and consistently identify and select all functions of the control device.

        -- Quickly and reliably identify what item on the display is “active” as a result of cursor positioning, as well as what function will be performed if the item is selected using the selector buttons and/or changed using the multi-function control.

        -- Determine quickly and accurately the function of the control without extensive training or experience.

·        Labels of graphical controls accessed by a cursor device such as a trackball should be included on the graphical display. When menus lead to additional choices such as submenus, the menu label should provide a reasonable description of the next submenu. [AC 25.1302-1, 5-4.c(2)(a)]

        See also: AMC 25.1302, 5.3.3.b which is worded slightly differently; Chapter 6.4.5 Cursor Control Devices (CCDs)

·        Use terms, icons, or abbreviations recommended in applicable FAA policy and other standards (e.g., International Civil Aviation Organization (ICAO), Document 8400, ICAO Abbreviations and Codes, Sixth Edition, date 2004 or SAE ARP 4105B*, Abbreviations and Acronyms for Use on the Flight Deck, reaffirmed June 2004), for labels, when available. Otherwise, use labels that are in general use in aviation. [AC 20-175, 2-8.e]

        See also: AMC 25.1302, 5.3.3.b which is worded slightly differently; TSO-C165/RTCA DO-257A, 2.2.2

·        For controls using icons in lieu of text labeling, substantiate that pilots, with the minimum expected training program, can adequately perform their duties at an acceptable level of workload, as required by normal, non-normal, and emergency situations. If appropriate, consider incorporating icons in controls to complement rather than replace text labels (e.g., continuous text display, temporary “mouseover” display). [AC 20-175, 2-8.f]

·        If multiple controls exist for the same function, clearly label all such controls. Exceptions can include alternate controls that provide flexibility to accommodate a wide range of pilots. For example, experienced users might choose less-intuitive methods in order to gain a performance advantage such as speed. Double-clicking or push-and-hold are examples that are generally not recommended as a sole method of operation, but may be acceptable as a secondary method (e.g., for advanced users). Show that multiple controls for the same function are acceptable, and do not result in confusion or inadvertent operation. [AC 20-175, 2-8.g]

·        If multiple controls exist (multi-crew aircraft) for the same function, show that there is sufficient information or other means available to make each crewmember aware of which control is currently functioning. [AC 20-175, 2-8.h]

        See also: AC 25.1302-1, 5-4.c(3)(a) and AMC 25.1302, 5.3.3.c which are worded slightly differently.

·        Use only one abbreviation and/or one icon for labeling a function. This is to prevent confusion when a label appears in multiple locations. [AC 20-175, 2-8.i]

·        Ensure that the labels resist scratching, hazing, erasure, disfigurement, and other legibility degradation that might result from normal use. [AC 20-175, 2-8.j]

·        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. [AC 20-175, 3-3.a]

·        Ensure that pop-up text that describes a control’s function does not result in unacceptable distractions, interference, or clutter. [AC 20-175, 3-3.b]

·        If a control activates several different functions based on sequential commands or selections, clearly label each of the functions. [AC 20-175, 3-3.c]

·        There should be a clear indication when any control is in an altered state and not the default (e.g., if a knob is pulled out and functions differently). [TSO-C146c/RTCA DO-229D, 2.2.1.1.4.1] 

        See also: Chapter 6.3 Operation of Controls

·        Control markings should be evaluated to ensure that a logical and consistent labeling convention has been applied throughout the cockpit. The evaluation should also consider electronic control labeling, particularly as applied across all display pages. It is important that the terminology chosen for that control function is immediately and clearly understood by the expected pilot population. The evaluation should verify that the terms chosen conform to standardized aviation conventions. [PS-ACE100-2001-004, Appendix A] 

·        Pilots must be able to quickly and reliably identify the function being controlled by these software labels. The standard that should be applied is that pilots must be capable of performing control-related tasks to the same performance standards as would result from the use of conventional controls unless the decrement is inconsequential and the design enables other significant performance gains or design simplifications. [PS-ACE100-2001-004, Appendix A] 

·        All control markings should be evaluated to ensure they are visible and evenly illuminated during both night and day operations. It should also be noted that font size (variations, e.g., character stroke size, width and height) of the illuminated displays can affect readability and perceived brightness. Variations in font size may create perceived lighting imbalances. (Reference ARP4103 for recommendations.) [PS-ACE100-2001-004, Appendix A]

Multi-function Controls 

·        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. [AC 20-175, 3-1.d]

·        If a control is used to perform multiple functions, the functionality shall be clearly distinguished. [TSO-C146c/RTCA DO-229D, 2.2.1.1.4.1]

·        Designs should generally avoid multi-function controls with hidden functions, because they increase both crew workload and the potential for error. [AMC 25.1302, 5.7.5**]

Multi-function Controls: Menus and Navigation

See also: Chapter 5.2 Managing Display Information for additional considerations on use of menus.

·        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. [AC 20-175, 3-6]

·        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 sub-menus should be designed to ensure timely access to the desired option without over-reliance on memorization of the menu structure. [AC 20-175, 3-6.a]

·        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. [AC 20-175, 3-6.b]

See also: AMC 25.1302, 5.3.4 which is worded slightly differently.

·        Fit top-level control menu pages (e.g., primary or “home” page) entirely on the display (i.e., do not require scrolling). [AC 20-175, 3-6.c]

·        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). [AC 20-175, 3-6.d]

·        Provide feedback from page navigation that is an unambiguous indication of the current location. [AC 20-175, 3-6.e]

Multi-function Controls: Voice Recognition and Voice Activated

·        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. [AC 20-175, 3-7.a]

·        Provide a simple and readily apparent means to deactivate the voice recognition or voice activated system. [AC 20-175, 3-7.b]

·        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). [AC 20-175, 3-7.c]

Powerplant Controls

·        Each powerplant control must be located, arranged, and designed under §§ 25.777 through 25.781 and marked under § 25.1555. [14 CFR 25.1141]

        See also: 14 CFR 23.1141(a), 27.1141(a), 29.1141(a) which are worded slightly differently.

·        Each control must be located so that it cannot be inadvertently operated by persons entering, leaving, or moving normally in, the cockpit. [14 CFR 25.1141(a), 29.1141(b)]

·        Each flexible control must be approved or must be shown to be suitable for the particular application. [14 CFR 25.1141(b)]

        See also: 14 CFR 23.1141(b), 27.1141(b), 29.1141(b) which are worded slightly differently.

·        Each control must have sufficient strength and rigidity to withstand operating loads without failure and without excessive deflection. [14 CFR 25.1141(c)]

        See also: 14 CFR 23.1141(d), 29.1141(e) which are worded slightly differently.

·        Each control must be able to maintain any set position without constant attention by flight crewmembers and without creep due to control loads or vibration. [14 CFR 25.1141(d)]

        See also: 14 CFR 23.1141(c), 27.1141(c), 29.1141(c) which are worded slightly differently.

·        No single failure or malfunction, or probable combination thereof, in any powerplant control system may cause the failure of any powerplant function necessary for safety. [14 CFR 23.1141(e), 27.1141(e)]  

·        For powerplant fuel controls: [14 CFR 25.1555(c)]

        (1)   Each fuel tank selector control must be marked to indicate the position corresponding to each tank and to each existing cross feed position;

        (2)   If safe operation requires the use of any tanks in a specific sequence, that sequence must be marked on, or adjacent to, the selector for those tanks; and

        (3)   Each valve control for each engine must be marked to indicate the position corresponding to each engine controlled.

        See also: 14 CFR 23.1555(c), 27.1555(b), 29.1555(b) which are worded slightly differently.

Controls for Data Entry

·        Data entry controls should allow pilots to easily recover from typical inputs errors, such as a simple keyboarding error or an incorrect auto fill. [AC 20-175, 2-11.d]

·        Controls for data entry must support the pilot when entering required data to support the intended function, per § 2X.1301. Show that the controls are acceptable for data entry speed, accuracy, error rates, and workload. [AC 20-175, 2-11.a]

·        If data entry involves multiple steps, make sure that each step is clearly discernable. [AC 20-175, 2-11.b]

·        During data construction, ensure that automatically constructed data is clearly discernable from manually constructed data. Regardless of how the data was constructed, the system should allow pilots to readily determine the data that is entered into the system. [AC 20-175, 2-11.c]

·        Previously approved controls for data entry have used physical configurations and design features based on the following: [AC 20-175, 2-11.e]

        (1)   Letter keys that are arranged in a QWERTY format (preferred) or alphabetically.

        (2)   Numeric keypads that are arranged in a 3x3 matrix with zero (0) at the bottom.

        (3)   Concentric knob assemblies that contain no more than two knobs per assembly.

        (4)   Cursors that are automatically placed in the first data entry field.

        (5)   Data entry fields that are large enough to show all of the entered data without scrolling.

        (6)   Partitioning of long data items into shorter sections for both data entry and feedback.

·        Time-outs (e.g., from interruptions in the pilot's data entry task) and related automated data entry features should be predictable and easily recognized by the pilot. [AC 20-175, 2-11.f]

Controls for Automated Systems

·        Automated systems can perform various tasks selected by and supervised by the flightcrew. Controls should be provided for managing functionalities of such a system or set of systems. The design of such “automation specific” controls per § 25.1302 should enable the flightcrew to do the following: [AC 25.1302-1, 5-6.c(5)(a)]

        1  Safely prepare the system for the immediate task to be executed or the subsequent task to be executed. Preparation of a new task (for example, new flight trajectory) should not interfere with, or be confused with, the task currently being executed by the automated system.

        2  Activate the appropriate system function and clearly understand what is being controlled and what the flightcrew expects. For example, the flightcrew must clearly understand they can set either vertical speed or flight path angle when they operate a vertical speed indicator.

        3  Manually intervene in any system function, as required by operational conditions, or revert to manual control. For example, manual intervention might be necessary if a system loses functions, operates abnormally, or fails.

        See also: AMC 25.1302, 5.5.3 which is worded slightly differently.

Continued Airworthiness

·        Title 14 CFR 2X.1529 requires instructions for continued airworthiness of equipment. Include any limitations or considerations for the conditions in which controls are operated, replaced, or serviced. For example: [AC 20-175, 2-12.a]

        -   How should controls be serviced to ensure continued compliance with 14 CFR 2X.671, requiring easy, smooth, positive operation?

        -   Will controls need cleaning from skin oils and perspiration, in order for labels to be legible?

        -   What type of interference may impede safe operation?

        -   Is the control susceptible to failure if exposed to liquids (e.g., spilled coffee or soda)?

        -   What maintenance or inspection should be conducted over a given time interval?

·        Design controls to minimize degradation (e.g., scratching, hazing) from operational use. [AC 20-175, 2-12.b]

·        Define a reasonable maintenance and inspection interval for each control, along with verification tests that are conducted at each interval in the instructions for continued operational safety. [AC 20-175, 2-12.c]

General

·        The system should clearly indicate when a control’s function is being performed by automation (e.g., with an indication showing that the function is not available). (Billings, 1997; Wickens and Holland, 2000)

·        Controls should be usable in the full range of turbulence conditions. [RTCA DO-256, 2.1.2.2]

·        The design dimensions of the input device should be compatible with human anthropometric considerations (i.e., anatomy and physiology). (Cardosi and Murphy, 1995)

·        Soft control buttons should be consistent in size and shape. (Wagner et al., 1997)

·        Differing types of controls shall be limited to the minimum, sense of actuation standardized and related effect made as uniform as possible. Keyboards and rotary controls are preferred to thumb wheels and slew controls. [SAE ARP4102, 5.1.1.3]

·        If multiple input devices are used, the input devices selected should be compatible. The overall system design should not require frequent switching among different input devices (Cardosi and Murphy, 1995)

Control Labels

·        Soft control labels (e.g., response options associated with line select keys that may change depending upon what page is displayed) should be displayed in a consistent location on all display screens. [RTCA DO-256, 2.1.3.5]

·        Soft control labels shall be unambiguously associated with the control they label (e.g., either through location or through an indicator of which control is associated with the label). [RTCA DO-256, 2.1.3.5]

·        Labels should not be placed directly on rotating controls because the orientation of the control will change when it is manipulated. (McAnulty, 1995)

·        Lines should be used to connect soft labels to the controls they identify to minimize parallax issues. (Yeh, 2004)

·        Soft function key labels should be drawn in a reserved space outside of the main content area. (Chandra et al., 2003)

·        When used for function selection, the selected function shall be clearly indicated and the selector position shall be identified by a distinguishable detent. [SAE ARP4102, 5.3.1.3]

·        The face of the rotary control shall be clearly marked to enhance identification of the control position. [SAE ARP4102, 5.3.1.4]

Coding and Consistency

·        If coding methods are used to differentiate controls, the application of the coding should be consistent throughout the system and with the flight deck design philosophy. (MIL-STD-1472G, 5.1.1.4.1)

·        Controls that perform identical functions from one display system to another should be coded in the same way. (Sanders and McCormick, 1993)

·        If controls are coded by size, only three to five sizes should be used. Similar controls should differ in size by at least 20%, and the control diameters should differ by at least 0.5 in (13 mm). (McAnulty, 1995)

·        The shape of the control should be unique and, where possible, meaningful so it can be identified directly with the function. (Yeh, 2004; MIL-STD-1472G, 5.1.1.4.4)

·        If controls are coded by shape, no more than 10 different shapes should be used. The shapes should be distinguishable tactually and visually and easily associated with their function. The shape should not interfere with the manipulation of the control. Sharp edges should be avoided. (McAnulty, 1995)

·        The color of controls should be black or gray. (McAnulty, 1995; MIL-STD-1472G, 5.1.1.4.5.a)