General

·        Flightcrew alerts must: [14 CFR 25.1322 (a)]

        (1)   Provide the flightcrew with the information needed to:

                (i)    Identify non-normal operation or airplane system conditions, and

                (ii)   Determine the appropriate actions, if any.

        (2)   Be readily and easily detectable and intelligible by the flightcrew under all foreseeable operating conditions, including conditions where multiple alerts are provided.

        (3)   Be removed when the alerting condition no longer exists.

·        Alerting messages should differentiate between normal and abnormal indications. [AC 23.1311-1C, 18.3]

·        Only non-normal airplane-system conditions and operational events that require flightcrew awareness to support flightcrew decision making and facilitate the appropriate flightcrew response should cause an alert. However, conditions that require an alert depend on the specific system and airplane design, and overall flight-deck philosophy. [AC 25.1322-1, 5.c(1)]

·        Conditions that do not require flightcrew awareness should not generate an alert. [AC 25.1322-1, 5. a]

·        The number and type of alerts required should be determined by the unique situations that are being detected and by the crew procedures required to address those situations. [AC 25.1329-1B, 45.d(2)]

·        Provide individual alerts for each function essential for safe operation. [AC 23.1311-1C, 18.3]

·        Alerting conditions. Establish how airplane system conditions or operational events that require an alert (for example, engine overheating, windshear, etc.), will be determined. [AC 25.1322-1, 5.c(9)]

·        Annunciations should only be indicated while the condition exists. [AC 25-11A, 31.f(1)(b)]

·        Annunciations and indications should be operationally relevant and limited to minimize the adverse effects on flightcrew workload. [AC 25-11A, 31.f(1)(a)]

·        The equipment shall provide the capability to test all external annunciators. [TSO-C146c/RTCA DO-229D, 2.2.1.5.1]

·        Timely alerts for each phase of flight should be provided when any operating limit is reached or exceeded for the required powerplant parameter. [AC 23.1311-1C, 9.3.b]

·        An alert should be given when the information presented to the flightcrew is no longer meeting the required integrity level, in particular when there is a single sensor or loss of independence. [AC 25-11A, 36.e(2)(f)]

·        The latency period induced by the display system, particularly for alerts, should not be excessive and should take into account the criticality of the alert and the required crew response time to minimize propagation of the failure condition. [AC 25-11A, 21.e(8)]

·        Design of Controls, Indications, and Alerts. These features must be designed to minimize flightcrew errors and confusion. [See § 25.1329(i)] Indications and alerts should be presented in a manner compatible with the procedures and assigned tasks of the flightcrew and provide the necessary information to perform those tasks. The indications must be grouped and presented in a logical and consistent manner and should be visible from each pilot’s station under all expected lighting conditions. [See § 25.1329(i)] The choice of colors, fonts, font size, location, orientation, movement, graphical layout, and other characteristics—such as steady or flashing—should all contribute to the

        effectiveness of the system. Controls, indications, and alerts should be implemented in a consistent manner. [AC 25.1329-1B, 42.b]

        See also: Chapter 9 Error Management, Prevention, Detection, and Recovery

Alerting Philosophy

·        When developing a flightcrew-alerting system use a consistent philosophy for alerting conditions, urgency and prioritization, and presentation. [AC 25.1322-1, 5.b]

·        Annunciations and indications should be clear, unambiguous, timely, and consistent with the flight deck design philosophy. [AC 25-11A, 31.f(1)(b)]

        See also: AC 27-1B, Chapter 3 AC 27 MG 18, g(7) and AC 29-2C, Chapter 3 AC 29 MG 18, g(7) which are worded slightly differently.

·        The alerting philosophy should describe the format and content for visual information. Use consistent format and content that includes the following three elements: [AC 25.1322-1, Appendix 1, 2.b(2)]

        -       The general heading of the alert (for example, HYD, FUEL)

        -       The specific subsystem or location (for example, L-R, 1-2),

        -       The nature of the condition (for example, FAIL, HOT, LOW)

·        Use a consistent philosophy for the format and content of the visual information to clearly indicate both the alert meaning and condition. The objectives of the corresponding text message format and content are to direct the flightcrew to the correct checklist procedure, and to minimize the risk of flightcrew error. [AC 25.1322-1, Appendix 1, 2.b1)]

·        Use logic-based integrated alerting systems to ensure that alerting system elements are synchronized and provide the proper alert presentation format for each urgency level. [AC 25.1322-1, 5.c(5)]

·        Establish a consistent alert presentation scheme (for example, location of the alert on the flight deck, alert combinations [aural, visual, tactile], information presented in the alert message, and color and graphical coding standardization). Also, determine the format in which that alert will be presented (for example, structure and timing of alert messages) to support the alerting function’s purpose. [AC 25.1322-1, 5.c(11)]

·        While strongly encouraged, the FAA recognizes it is not always possible to provide a consistent flightcrew interface. Despite conformance with a flightdeck design philosophy, principles of consistency, etc., it is possible to negatively impact flightcrew workload. As an example, all the auditory alerts in a design may adhere to a flightdeck alerting philosophy, but the number of alerts may be unacceptable. [AC 25.1302-1, 5-8.c(1)]

        See also: AMC 25.1302, 5.7.3 which is worded slightly differently.

Field-of-View/Location

See also: Chapter 2.3 Field-of-View

·        In most applications, critical information that is considered to be essential for safe flight, with warning or cautionary information that requires immediate pilot action or awareness, should be placed in the primary field-of-view. [AC 23.1311-1C, 15.2]

·        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. [AC 23.1311-1C, 15.4, Note 4]

·        Annunciations and indications should be consistently located in a specific area of the electronic display. Annunciations that may require immediate flightcrew awareness should be located in the flightcrew’s forward/primary field of view. [AC 25-11A, 31.f(2)]

        See also: AC 23.1311-1C, 18.1 which is worded slightly differently.

·        The visual-alert information should be located so that both pilots are able to readily identify the alert condition. [AC 25.1322-1, Appendix 1, 2.a(2)]

·        The horizontal (and vertical) deviation(s) display(s) and failure annunciation should be located within the pilot's primary field of view, as should any indication requiring immediate aircrew action. [AC 20-138C, 11-8.b(4)]

See also: Chapter 2.2 Display Installation and Integration

·        Displays used for waypoint sequencing, start of a turn, turn anticipation, active waypoint, distance to active waypoint, desired track and actual track (track angle error), and automatic mode switching should be located within the pilot’s primary field of view, or on a readily accessible display page. [AC 20-138C, 14-2.b]

        See also: Chapter 2.2 Display Installation and Integration

·        Displays used for loss of integrity monitoring, TO/FROM indication, and approach mode annunciation should be located within the pilot’s primary field of view. [AC 20-138C, 14-2.b(1)]

        See also: Chapter 2.2 Display Installation and Integration

·        Traditionally, 14 CFR part 23 airplanes with “classic” analog instrumentation in the “basic T” arrangement have included the center radio stack within the allowable field of view to satisfy this guidance. There is no intent for this AC to change that long-standing guidance. [AC 20-138C, 14-2.b(2)]

·        Master visual alerts for warnings (master warning) and cautions (master caution) should be located in each pilot’s primary field of view. [AC 25.1322-1, Appendix 1, 1.a]

·        To determine the quantity of displays that provide warning, caution, and advisory alerts, take into account the combination of ergonomic, operational, and reliability criteria, as well as any physical space constraints in the flight deck. [AC 25.1322-1, Appendix 1, 2.a(1)]

·        All warning and caution visual information linked to a master visual alert should be grouped together on a single dedicated display area. There may be a separate area for each pilot. Advisory alerts should be presented on the same display area as warning and caution information. The intent is to provide an intuitive and consistent location for the display of information. [AC 25.1322-1, Appendix 1, 2.a(3)]

·        Time-Critical warning visual information should appear in each pilot’s primary field of view. [AC 25.1322-1, Appendix 1, 3.a]

        Note:  The primary flight display (PFD) is used as a practical and preferred display for displaying the time-critical warning alerts since the pilot constantly scans the PFD. Integrating time-critical information into the PFD depends on the exact nature of the warning. For example, a dedicated location on the PFD may be used both as an attention-getting function and a visual information display by displaying alerts such as “WINDSHEAR,” “SINK RATE,” “PULL UP,” “TERRAIN AHEAD,” and “CLIMB, CLIMB.” In addition, graphic displays of target pitch attitudes for Airborne Alert and Collision Avoidance System (ACAS) II Resolution Advisories and Terrain may also be included. [AC 25.1322-1, Appendix 1, 3.a]

·        Information for error detection may …[be] indications provided to the flightcrew during normal monitoring tasks… Indications on instruments in the primary field of view used during normal

        operation may be adequate if the indications themselves contain information used on a regular basis and are provided in a readily accessible form. These may include mode annunciations and normal airplane state information such as altitude or heading. Other locations for the information may be

        appropriate depending on the flightcrew’s tasks, such as on the control-display unit when the task involves dealing with a flight plan. [AC 25.1302-1, 5-7.b.]

        See also: AMC 25.1302, 5.6.2 which is worded slightly differently; Chapter 9 Error Management, Prevention, Detection, and Recovery

Color

See also: Chapter 3.7 Color

·        Visual alert indications must: [14 CFR 25.1322 (e)]

        (1)   Conform to the following color convention:

                (i)    Red for warning alert indications.

                (ii)   Amber or yellow for caution alert indications.

                (iii)  Any color except red or green for advisory alert indications.

        (2)   Use visual coding techniques, together with other alerting function elements on the flight deck, to distinguish between warning, caution, and advisory alert indications, if they are presented on monochromatic displays that are not capable of conforming to the color convention in paragraph (e)(1) of this section.

·        If warning, caution, or advisory lights are installed in the cockpit, they must, unless otherwise approved by the Administrator, be -- [14 CFR 23.1322]

        (a)   Red, for warning lights (lights indicating a hazard which may require immediate corrective action);

        (b)   Amber, for caution lights (lights indicating the possible need for future corrective action);
(c)   Green, for safe operation lights; and

        (d)   Any other color, including white, for lights not described in paragraphs (a) through (c) of this section, provided the color differs sufficiently from the colors prescribed in paragraphs (a) through (c) of this section to avoid possible confusion.

        (e)   Effective under all probable cockpit lighting conditions.

        See also: 14 CFR 27.1322 and 29.1322, which are worded slightly differently.

·        Use of the colors red, amber, and yellow on the flight deck for functions other than flightcrew alerting must be limited and must not adversely affect flightcrew alerting. [14 CFR 25.1322 (f)]

·        The primary test for designation of color is: [AC 27-1B, AC 27.1322b(5); AC 29-2C, AC 29.1322a(8)]

        (i)    Red - Is immediate action required?

        (ii)   Amber - Is pilot action (other than immediate) required?

        (iii)  Green - Is safe operation indicated, and is the indication sufficiently distinct to prevent confusion with the landing gear down indication?

        (iv)  Other advisory lights - Is the meaning clear and distinct enough to prevent confusion with other annunciations? Do the colors which are utilized differ sufficiently from the colors specified above?

·        Where red, amber and yellow are proposed for non-flightcrew alerting functions, substantiate that there is an operational need to use these colors to provide safety related awareness information. Examples of acceptable uses of red, amber, or yellow for non-alerting functions include: [AC 25.1322-1, 11.g]

        -       Weather radar display (for areas of severe/hazardous weather conditions that should be avoided);

        -       TAWS terrain display (for local terrain relative to the current altitude).

·        The colors that are used for attention getting and alerting should be identifiable through the full range of normally expected flight deck illumination conditions. [TSO-C165/RTCA DO-257A, Appendix E E.3]

·        Green is usually used to indicate “normal” conditions; therefore, it is not an appropriate color for an advisory alert. An advisory alert is used to indicate a “non-normal” condition. [AC 25.1322-1, 11.a]

·        Displays must either conform to the alert color convention or, in the case of certain monochromatic displays not capable of conforming to the color conventions, use other visual coding techniques per § 25.1322(e). This is necessary so the flightcrew can easily distinguish the alert urgency under all foreseeable operating conditions, including conditions where multiple alerts are provided (§ 25.1322(a)(2)). [AC 25.1322-1, 8.c(3)]

·        For monochromatic displays that are not capable of conforming to the color convention required by § 25.1322(e)(2), use display coding techniques (for example, shape, size, and position) so the flightcrew can clearly distinguish between warning, caution, and advisory alerts. This requirement is similar to using selected color coding on multicolor displays that allows the flightcrew to easily distinguish between warning, caution, and advisory alerts (§ 25.1322(e)). These coding techniques must also meet the general alerting requirement in § 25.1322(a)(2) so the alerts are readily and easily detectable and intelligible by the flightcrew under all foreseeable operating conditions, including conditions where multiple alerts are provided. The wide use of monochromatic displays on the flight deck with flightcrew alerting is normally discouraged, except when an increased safety benefit is demonstrated, for example, a HUD used as a primary flight display. [AC 25.1322-1, 11.e]

·        A separate and distinct color should be used to distinguish between caution and advisory alerts. If a distinctive color is not used to distinguish between caution and advisory alerts, other distinctive coding techniques must be used to meet the general requirements of § 25.1322(a)(2) so that the flightcrew can readily and easily detect the difference between caution and advisory alerts. [AC 25.1322-1, 11.b]

·        The color displayed for the visual master warning alert must be the same color used for the associated warning alerts and the color displayed for the master caution alert must be the same color used for the associated caution alerts (§ 25.1322(e)(1)). [AC 25.1322-1, 11.c]

Format/Content

·        Any alert should be clear and unambiguous and should be consistent and compatible with other flight deck alerts. [AC 25.1329-1B, 45.d(2)]

·        Abnormal indications should be clear and unmistakable, using techniques such as different shapes, sizes, colors, flashing, boxing, outlining, etc. [AC 23.1311-1C, 18.3]

·        Alerts and symbols shall be distinctive and readily discernable from one another. [TSO-C146c/RTCA DO-229D, 2.2.1.1.4.1]

        See also: AC 25-11A, 31.c(3)(a) which is worded slightly differently; Chapter 3.3 Symbols

·        All alerts presented to the flightcrew, (for example, light, aural annunciation, engine-indication-and-crew-alerting system (EICAS) message, master caution) must provide the flightcrew with the information needed to identify the non-normal operational or airplane system condition and determine the corrective action, if any (§ 25.1322 (a)(1)). Appropriate flightcrew corrective actions

        are normally defined by airplane procedures (for example, in checklists) and are part of a flightcrew training curriculum or considered basic airmanship. [AC 25.1322-1, 5.c(2)]

·        Include the appropriate combination of alerting system presentation elements, which typically include: [AC 25.1322-1, 5.c(4)]

        (a)   Master visual alerts

        (b)   Visual alert information (includes failure flag indications)

        (c)   Master aural alerts

        (d)   Voice information

        (e)   Unique tones (unique sounds)

        (f)    Tactile or haptic information

·        Use consistent wording, position, color and other shared attributes (for example, graphic coding) for all alerting annunciations and indications. [AC 25.1322-1, 10.a]

·        If alerts are presented on a limited display area, use an overflow indication to inform the flightcrew that additional alerts may be called up for review. Use indications to show the number and urgency levels of the alerts stored in memory. [AC 25.1322-1, Appendix 1, 2.b(4)]

·        An alphanumeric font should be of a sufficient thickness and size to be readable when the flightcrew are seated at the normal viewing distance from the screen. [AC 25.1322-1, Appendix 1, 2.b(6)]

See also: Chapter 3.2 Labels

        Note 1:   Minimum character height of 1/200 of viewing distance is acceptable (for example, a viewing distance of 36 inches requires a 0.18 inch character height on the screen) per DOD-CM-400-18-05, Department of Defense User Interface Specifications for the Defense Information Infrastructure, Defense Information Systems Agency, February 1998, p 12-1). [AC 25.1322-1, Appendix 1, 2.b(6)]

        Note 2:   Arial and sans serif fonts are acceptable for visual alert text. The size of numbers and letters required to achieve acceptable readability depends on the display technology used. Stroke width between 10% and 15% of character height appears to be best for word recognition on text displays. Extensions of descending letters and ascending letters should be about 40% of letter height. [AC 25.1322-1, Appendix 1, 2.b(6)]

        Note 3:   Different fonts can be used to differentiate between new and previously acknowledged visual alert information. [AC 25.1322-1, Appendix 1, 2.b(6)]

·        A “collector message” can be used to resolve problems of insufficient display space, prioritization of multiple alert conditions, alert information overload, and display clutter. Use collector messages when the procedure or action is different for the multiple fault condition than the procedure or action for the individual messages being collected. For example, non-normal procedures for loss of a single hydraulic system are different than non-normal procedures for loss of two hydraulic systems. [AC 25.1322-1, Appendix 1, 2.b(5)]

Blinking/Flashing

·        The use of blinking should be limited because it can be distracting and excessive use reduces the attention getting effectiveness. Blinking rates between 0.8 and 4.0 Hertz should be used, depending on the display technology and the compromise between urgency and distraction. If blinking of an information element can occur for more than approximately 10 seconds, a means to cancel the blinking should be provided. [AC 25-11A, 31.f(4)]

·        The use of flashing lights should be minimized. If a flashing feature is used, it should be controllable through pilot action so that flashing annunciation does not persist indefinitely. The indicator should be so designed that if it is energized and the flasher device fails, the light will illuminate and burn steadily. [AC 27-1B, AC 27.1322b(8); AC 29-2C, AC 29.1322a(11)]

Luminance

·        The visual alert information should be bright enough so that both pilots are able to readily identify the alert condition in all ambient light conditions. [AC 25.1322-1, Appendix 1, 2.d(1)]

·        The luminance of the visual alert information display may be adjusted automatically as ambient lighting conditions change inside the flight deck. A manual override control may be provided to enable the pilots to adjust display luminance. [AC 25.1322-1, Appendix 1, 2.d(2)]

·        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. [AC 23.1311-1C, 18.1]

·        Visual annunciations must be consistent with the criticality of the annunciation and must be readable under all normal cockpit illumination conditions. Visual annunciations must not be so bright or startling as to reduce pilot dark adaptation. [AC 20-138C, 15-3.b; TSO-C146c/RTCA DO-229D, 2.2.1.1.5]

·        Characters used on alert and status indications should be of the size and brightness necessary to be readable without error or strain under anticipated lighting conditions. Brightness shall be controllable, which does not preclude automatic adjustment. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5.1]

Auditory Alerts, Annunciations, and Indications

·        The applicant should show display text and auditory messages are distinct and meaningful for the information presented. [AC 25.1302-1, 5-5.b(4)(e); AMC 25.1302 5.4.2.e]

·         Auditory alerts have the advantage of being useful regardless of the pilots head and eye orientation, but their use should be considered with care to avoid compromising other auditory alerts that may be available in the cockpit. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5]

·        Auditory alerts should not be used as the sole source of information, but to draw the pilot’s attention to information on a visual display. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5]

·        The number of auditory alarms should be kept to the minimum necessary to provide the desired result. [PS-ACE100-2001-004, Appendix A]

·        Audible alarms should be sufficiently loud and of appropriate pitch quality, duration and pattern. Alarms should be easily deactivated (but not easily deactivated inadvertently). Audible alarms must not interfere with other aircraft audio alarms or alerts of higher priority (e.g. stall warnings, gear warning, or chip-detect). [AC 20-138C, 17-3.b]

·        If provisions for the use of communication headsets are provided, it must be demonstrated that the flightcrew members will receive all aural warnings under the actual cockpit noise conditions when the airplane is being operated when any headset is being used. [14 CFR 23.1431(e)]

·        All aural alerts need to be evaluated with and without headsets to assess their effectiveness and acceptability under all ambient noise conditions that may be encountered in the operational environment. There have been problems created by using active noise reduction headsets in older cockpits that have an alert sounded only in the cabin and not in the cockpit. The aircraft evaluations

        should also include the examination of an active noise reduction (ANR) system if it is going to be used on the airplane. [PS-ACE100-2001-004, Appendix A]

·        Regardless of the method chosen to present auditory alerts, they should be easily detected and quickly understood in all ambient noise conditions. [PS-ACE100-2001-004, Appendix A]

·        If using aural alerts with multiple meanings, a corresponding visual, tactile, or haptic alert should be provided to resolve any potential uncertainty relating to the aural alert and clearly identify the specific alert condition. [AC 25.1322-1, 5.c(8)]

·        If an audible alarm is used, provisions must be provided for the crew to silence the alarm. [PS-ANM100-2001-00114, 4(a)(v)]

·        Because auditory information presentation is transient, designers should be careful to avoid the potential for competing auditory presentations that may conflict with each other and hinder interpretation. Prioritization and timing may be useful for avoiding this potential problem. [AC 25.1302-1, 5-5.c(2)(c)]

See also: AMC 25.1302, 5.4.3.b which is worded slightly differently.

·        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. [AC 23.1311-1C, 15.4, Note 4]

·        Aural alerts should be prioritized so that only one aural alert is presented at a time. If more than one aural alert needs to be presented at a time, each alert must be clearly distinguishable and intelligible to the flightcrew (§ 25.1322(a)(2)). [AC 25.1322-1, 8.b(1)]

·        When aural alerts are provided, an active aural alert should finish before another aural alert begins. However, active aural alerts must be interrupted by alerts from higher urgency levels if the delay to annunciate the higher-priority alert impacts the timely response of the flightcrew (§ 25.1301(a)). If the condition that triggered the interrupted alert is still active, that alert may be repeated once the higher-urgency alert is completed. If more than one aural alert requires immediate awareness and the interrupted alert(s) affects the safe operation of the airplane, an effective alternative means of presenting the alert to the flightcrew must be provided to meet the requirements of § 25.1322(a)(1) and (a)(2). [AC 25.1322-1, 8.b(2)]

·        Annunciation of any system level warning, caution, and advisory alert should be compatible with the alert schematic. Prioritize systems information displayed to allow ready access to critical information. Less critical information may be less accessible. Provide a means for the pilot to select higher priority information as needed with a single entry on the control panel or keypad. [AC 23.1311-1C, 18.4]

Voice/Speech Information

·        Additional reasons for using voice information include: [AC 25.1322-1, Appendix 2, 3]

        a.     Limiting the number of unique tones.

        b.     Transferring workload from the visual to the auditory channel.

        c.     Enhancing the identification of an abnormal condition and effectively augmenting the visual indication without replacing its usefulness.

        d.     Providing information to the flightcrew where a voice message is preferable to other methods.

        e.     Assuring awareness of an alert no matter where the pilot’s eyes are pointed.

·        The voice should be distinctive and intelligible. [AC 25.1322-1, Appendix 2, 3.f(1)(a)]

·        The voice should include attention-getting qualities appropriate for the category of the alert, such as voice inflection. [AC 25.1322-1, Appendix 2, 3.f(1)(b)]

·        Voice inflection may be used to indicate a sense of urgency. However, we do not recommend using an alarming tone indicating tension or panic. Such a tone may be inappropriately interpreted by flightcrews of different cultures. Depending on the alerting condition, advising and commanding inflections may be used to facilitate corrective action, but the content of the message itself should be sufficient. [AC 25.1322-1, Appendix 2, 3.f(2)]

·        Aural voice alerting must be audible to the flightcrew in the worst-case (ambient noise) flight conditions whether or not the flightcrew is wearing headsets (taking into account the headsets’ noise attenuation characteristics) (§ 25.1301(a)). Aural voice alerting should not be so loud and

        intrusive that it interferes with the flightcrew taking the required action. The minimum volume achievable by any adjustment (manual or automatic) (if provided) of aural voice alerts should be

        adequate to ensure it can be heard by the flightcrew if the level of flight deck noise subsequently increases. [AC 25.1322-1, Appendix 2, 3.f(3)(a)]

·        The onset of voice information should occur: [AC 25.1322-1, Appendix 2, 3.g(1)]

        (a)   In a timeframe appropriate for the alerting condition and the desired response.

        (b)   Simultaneously with the onset of its related visual alert information. Any delays between the onset of the voice information and its related visual alert should not cause flightcrew distraction or confusion.

        (c)   Simultaneously at each pilot’s station, if more than one source of the voice information is provided for the same condition, so that intelligibility is not affected.

·        The duration of voice information associated with time-critical warnings should continue until the alerting condition no longer exists (for example, terrain warning). The voice information should be repeated and non-cancelable during this time. [AC 25.1322-1, Appendix 2, 3.g(2)]

·        Voice information associated with time-critical warnings and cautions should not be repeated if it interferes with the flightcrew’s ability to respond to the alerting condition (for example, windshear warning, or ACAS II resolution advisory). [AC 25.1322-1, Appendix 2, 3.g(3)]

·        To support the flightcrew in taking corrective action voice information associated with warnings should be repeated and non-cancelable if the flightcrew needs continuous awareness that the condition still exists. [AC 25.1322-1, Appendix 2, 3.g(4)]

·        Voice information associated with warnings should be repeated and cancelable if the flightcrew does not need continuous aural indication that the condition still exists (for example, Cabin Altitude Warning or Autopilot Disconnect). [AC 25.1322-1, Appendix 2, 3.g(5)]

·        Reset the alerting mechanisms after cancelling them so they will annunciate any subsequent fault condition. [AC 25.1322-1, Appendix 2, 3.g(6)]

·        For voice alerts associated with a caution alert, the corresponding voice information should either: [AC 25.1322-1, Appendix 2, 3.g(7)]

        (a)   Be limited in duration (for example, ACAS II Traffic Advisory or Windshear Caution), or

        (b)   Be continuous until the flightcrew manually cancels it or the caution condition no longer exists.

·        The content should take into account the flightcrew’s ability to understand the English language. [AC 25.1322-1, Appendix 2, 3.h(1)]

·        When practical, voice information should be identical to the alphanumeric text message presented on the visual information display. If that is not possible, the voice information and alphanumeric message should at least convey the same information, so it is readily understandable and initiates the proper pilot response. [AC 25.1322-1, Appendix 2, 3.h(2)]

·        For warning and caution alerts, the content of voice information must provide an indication of the nature of the condition triggering the alert (§ 25.1322(a)(2)). The voice information should be descriptive and concise. [AC 25.1322-1, Appendix 2, 3.h(4)]

·        For time-critical warnings, the content and vocabulary of voice information must elicit immediate (instinctive) directive corrective action (§ 25.1322(a)(2)). In order to do this, it should identify the condition triggering the alert. In some cases, it may also be necessary to provide guidance or instruction information. [AC 25.1322-1, Appendix 2, 3.h(3)]

·        The content should be consistent with any related visual information display (for example, Aural: “Pull up”; Visual: “Pull up” on the PFD.) [AC 25.1322-1, Appendix 2, 3.h(5)]

·        Structure voice information that uses more than one word so if one or more words are missed the information will not be misinterpreted (for example, avoid the word “don’t” at the beginning of a voice message). [AC 25.1322-1, Appendix 2, 3.h(6)]

·        Design voice information so the flightcrew can easily distinguish one spoken word message from another to minimize confusion. [AC 25.1322-1, Appendix 2, 3.h(6)]

General

·        The Human Computer Interface shall indicate functions that are available for use from those that are not, based on the current context of the system status. [RTCA DO-256, 3.2.1.2.7]

·        Critical alarms should be easily distinguishable from non-critical alarms. (McAnulty, 1995)

·        To increase the pilot’s probability of detecting a visual alert, visual alerts should be large, high in brightness compared to the rest of the display, or employ motion. (McAnulty, 1995)

·        Critical or abnormal data should be highlighted using reverse video, shadows, brightness, or color. The levels and colors used must be distinctive and easily identified to be effective. (Cardosi and Murphy, 1995; Smith and Mosier, 1986)

·        The presentation of multiple alerts in sequence should be separated in time so that each alert can be identified. (Cardosi and Murphy, 1995; Palmer et al., 1995)

Format/Content

·        Visual alerts should subtend at least 1º of visual angle. In general, to attract attention, the visual angle subtended by the characters composing the text message should be greater than that for normal text. (Cardosi and Murphy, 1995)

·        When lighted words must attract attention, the minimum height of the letters should be 0.2 in (5.1 mm). (McAnulty, 1995)

Blinking/Flashing

·        Short-term flashing or intermittent signals (approximately 10 seconds or flash until acknowledge) should be used only for the most urgent warnings; these signals are effective attention getters but can be distracting. A permanent or long term flashing symbol that is noncancellable should not be used. (McAnulty, 1995)

·        If short-term flashing is used to convey an alert status, each flash should have a minimum duration of 0.05 seconds. (McAnulty, 1995)

·        Flashing/blinking should be used as an alert only. Flashing/blinking should not be used to highlight text or routine information. In particular, text that must be read should not blink or flash. (Garner and Assenmacher, 1997)

·        The use of flash coding should be kept to a minimum. [GAMA Publication No. 10, 7.1.5.1]

·        If blinking or flashing is used, less than half of the lights in the background should blink or flash simultaneously. A blink-free background will maximize detectability. (Cardosi and Murphy, 1995; GAMA Publication No. 10)

·        If blinking is used to code information, no more than two levels should be used. (MIL-STD-1472G, 5.2.2.3.4)

·        Pointing cursors should not blink. The size and image quality of the pointing cursor should be consistent across all display locations. (NASA, 1995, 9.6.3.2.1.1)

·        If blinking is used to call attention to the place holding cursor, the default blink rate should be 3 Hz. If the blink rate is user-selectable, the blink rate should be between 3 to 5 Hz. (NASA, 1995, 9.6.3.2.1.2)

Auditory Alerts, Annunciations, and Indications

·        The recommendations for the number of auditory signals range from four to six sounds. When workload and time pressure are high, the number of auditory signals should be limited to three or four sounds. (Cardosi and Murphy, 1995; McAnulty, 1995)

·        The audio signal should contain more than four components that are harmonically related. (CAA Paper 82017)

·        For pure tones, between four to five frequencies and between three to five intensities can be distinguished. (Cardosi and Huntley, 1993; Cardosi and Murphy, 1995)

·        The same auditory signal should not be associated with several visual displays, unless immediate discrimination of the sound is not critical to safety performance. (Garner and Assenmacher, 1997)

·        The minimum duration of the auditory signal should be 0.5 seconds. (McAnulty, 1995)

·        The frequency of an auditory signal should be between 500 Hz to 5,000 Hz; 500 Hz to 3,000 Hz is preferred. (Cardosi and Murphy, 1995; CAA Paper 80217; McAnulty, 1995)

        See also: Chapter 4.2 Managing Alerts

·        Warbling or undulating tones should be between 500 Hz and 1,000 Hz, with a rise and fall rate from 1 Hz to 3 Hz. (McAnulty, 1995)

·        The auditory signal should be at least 20 dB greater than the ambient noise level. The auditory signal should be at least 60 dB but less than 135 dB. (McAnulty, 1995)

·        A means to control the volume of the auditory signal should be provided. (Garner and Assenmacher, 1997)

·        Manual volume control should be avoided. (CAA Paper 80217)

·        The auditory signal should be intermittent and/or change over time. Steady-state signals become less noticeable over time. (Boucek, Veitengruber, and Smith, 1977)

·        Sound pulses for the auditory signal should have onsets and offsets 20 – 30 ms in duration. (CAA Paper 82017)

·        The sound pulses should be 100 – 150 ms long. To convey urgency, the inter-pulse interval should be less than 150 ms. For other auditory signals, the inter-pulse interval should be greater than 300 ms. (CAA Paper 82017)

·        The auditory signal should contain 5 or more pulses in a distinctive pattern. (CAA Paper 82017)

Voice/Speech Information

·        Voice messages requiring immediate action should be brief, use keywords. Voice messages conveying immediate awareness should use a full-phrase format and be repeated. (CAA Paper 82017)