General

·        Warning and caution alerts must: [14 CFR 25.1322 (c)]

        (1)   Be prioritized within each category, when necessary.

        (2)   Provide timely attention-getting cues through at least two different senses by a combination of aural, visual, or tactile indications.

        (3)   Permit each occurrence of the attention-getting cues required by paragraph (c)(2) of this section to be acknowledged and suppressed, unless they are required to be continuous.

·        To help ensure flightcrew awareness and timely action, appropriate alert(s)-normally a caution or warning-should be provided to the flightcrew for conditions that could require exceptional piloting skill or alertness for manual control following autopilot disengagement (for example, significantly out of trim conditions). [AC 25.1329-1B, 45.d(2)]

·        The activation of caution and warning lights should readily attract the attention of the appropriate crewmember while performing duties under both normal and high workload conditions. [AC 27-1B, AC 27.1322b(9); AC 29-2C, AC 29.1322a(12)]

·        Include a complete list of warnings, cautions, and annunciation messages in the AFM, supplemental AFM, and placards. If the manufacturer's Pilot Operating Guide is found adequate and acceptable, it may be referenced in the AFM or supplemental AFM as a means to satisfy this requirement. [AC 23.1311-1C, 22.8]

·        The functional elements used in the alerting and information functions for warning and caution alerts must provide timely attention-getting cues, resulting in immediate flightcrew awareness, through at least two different senses (§ 25.1322(c)(2)). [AC 25.1322-1, 6]

·        Provide one unique tone for master warning alerts and one unique tone for master caution alerts. [AC 25.1322-1, Appendix 2, 2.c(2)]

Warnings

·        Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors which could create additional hazards. [14 CFR 23.1309(b)(3), 25.1309(c), 29.1309(c)]

·        Warning Alerts. Several alert functional element combinations are used to comply with § 25.1322(c)(2) (two-senses requirement). The typical alert-element combinations for warning alerts (not including time-critical warning alerts) are shown below. [AC 25.1322-1, 6.a]

        (1) Master visual alert, visual alert information, and master aural alert.

        (2) Master visual alert, visual-alert information, and voice-alert information or unique alert tone.

        Note 1:   Voice-alert information may be preceded by a master aural alert. [AC 25.1322-1, 6.a]

        Note 2:   A tactile alert may be combined with a visual or aural alert to meet the § 25.1322 requirement for a combination of two senses. [AC 25.1322-1, 6.a]

·        Designs should mitigate the potential for crew error that could contribute to any additional hazards. The applicant should assess the consequences of inappropriate crew response to alerting conditions. Any likely misinterpretations of an alert should be examined to assess its potential for creating

        additional hazards. Evaluations should also include an assessment of the adequacy of the feedback given to the crew should they make an inappropriate response to a failure. Qualitative evaluations should also be used to supplement and verify analyses of pilot responses. These evaluations should include sufficient testing using a representative population of pilots to ensure acceptable interpretation of responses. [PS-ACE100-2001-004, Appendix A]

·        It is important to provide a warning, caution or alert signal that cannot be confused with either other cockpit visual or auditory displays, or both. It is also important that it aids the crew in determining the root cause of the problem and assists them in taking the appropriate corrective action. In addition, there must be immediate and effective feedback of the result(s) of that action. If an audio alert is used, the pilot must be able to discriminate it from all other audio signals. If multiple similar tones are used in the cockpit, it can complicate the pilot’s task and increase workload. Thus, it is important that auditory alerts be used judiciously. [PS-ACE100-2001-004, Appendix A]

·        A threat should trigger an automatic pop-up and the appropriate display on the ND, as well as the appropriate aural alert. Subsequent alerts of a higher priority may override the visual display, but the active aural alert should finish before another aural alert of equal or less urgency begins. [AC 23.1311-1C, 18.5]

·        Other functions, such as checklists, synoptic and expanded systems information, should only be shown when selected by the crew or displayed by phase of flight. [AC 23.1311-1C, 18.5]

·        Master Visual and Aural Alerts. A master visual alert and a master aural alert may not be warranted if other visual and aural means provide more timely attention-getting characteristics. If a master visual alert and/or a master aural alert are used, they should aid in the overall attention-getting characteristics and the desired flightcrew response and not distract the flightcrew from the time-critical condition. [AC 25.1322-1, 6.c]

Time-Critical Warnings

·        Some warnings may be so time-critical for the safe operation of the airplane that general alerts such as a master visual alert and a master aural alert may not provide the flightcrew with immediate awareness of the specific alerting condition that is commensurate with the level of urgency of flightcrew response necessary. In such cases, warning elements dedicated to specific alerting conditions should be provided that give the flightcrew immediate awareness without further reference to other flight deck indications. Examples of such time-critical warnings include reactive windshear and ground proximity. [AC 25.1322-1, 6.b]:

·        The alerting elements for time-critical warnings should include: [AC 25.1322-1, 6.b]

        -   Unique voice information or unique tone, or both, for each alerting condition, and

        -   Unique visual alert information in each pilot’s primary field of view for each alerting condition.

        Note:  A unique tactile alert sensed by each pilot can also meet the § 25.1322(c)(2) requirement for one of the two senses. [AC 25.1322-1, 6.b]

·        Unique tones associated with time-critical warnings and cautions should be repeated and non-cancelable until the alerting condition no longer exists (for example, stall warning), unless it interferes with the flightcrew’s ability to respond to the alerting condition. [AC 25.1322-1, Appendix 2, 2.d(5)]

·        Time-Critical Warning Visual Information. The corresponding visual and aural alert information should be consistent. [AC 25.1322-1, Appendix 1, 3.b(1)]

·        Time-critical warning visual information may be presented as a text message (for example, “WINDSHEAR”). Certain time-critical warning information, including guidance, may be presented graphically (for example, graphics representing an ACAS II Resolution Advisory). [AC 25.1322-1, Appendix 1, 3.b(2)]

·        If the alert is time-critical and shares a dedicated display region it must have the highest alerting priority to satisfy its intended function (§ 25.1301(a)). [AC 25.1322-1, 8.c(2)]

        See also: Chapter 8 Intended Function

·        Text messages and graphics for time-critical warning information must be red (§ 25.1322(e)(1)(i)). When displaying time-critical warnings on monochromatic displays, other graphic coding means must be used (§ 25.1322(e)). [AC 25.1322-1, Appendix 1, 3.b(3)]

·        The information must be removed when corrective actions (e.g. sink rate has been arrested, airplane climbed above terrain, etc.) have been taken, and the alerting condition no longer exists (§ 25.1322(a)(3). [AC 25.1322-1, Appendix 1, 3.b(4)]

·        To immediately attract the attention of the flightcrew and to modify their habit pattern for responding to warnings that are not time-critical, we recommend that a display for time-critical warnings subtend at least 2 square degrees of visual angle. [AC 25.1322-1, Appendix 1, 3.c]

Master Visual Alerts, Annunciations, and Indications

·        Following the guidance in paragraphs 5 and 6 of AC 25.1322-1, determine whether or not the added system features will require activation of an airplane master visual alert. [AC 25.1322-1, 14.b]

·        Unique visual alert information presented in each pilot’s primary field of view is acceptable in place of a master visual alert if it provides immediate awareness and sufficient attention-getting characteristics. However, an aural alert, such as an aural command to “pull up,” or another sensory cue, would still be required to meet § 25.1322(c)(2). [AC 25.1322-1, 6.c]

·        The onset of a master visual alert should occur: [AC 25.1322-1, Appendix 1, 1.b(1)]

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

        (b)   Simultaneously with the onset of its related master aural alert or unique tone, and its related visual alert information. Any delays between the onset of the master visual alert and its related master aural alert or unique tone, and its visual alert information should not cause flight crew distraction or confusion.

        (c)   Simultaneously at each pilot’s station (warnings, cautions).

        See also: Boucek, Veitengruber, and Smith, 1977

·        The master visual alert should remain on until it is cancelled either manually by the flightcrew, or automatically when the alerting condition no longer exists. [AC 25.1322-1, Appendix 1, 1.b(2)]

·        After the master visual alert is cancelled the alerting mechanisms should automatically reset to annunciate any subsequent fault condition. [AC 25.1322-1, Appendix 1, 1.b(3)]

·        In addition to color, steady state or flashing master visual alerts may be used, as long as the method employed provides positive attention-getting characteristics. If flashing is used, all master visual alerts should be synchronized to avoid any unnecessary distraction. [AC 25.1322-1, Appendix 1, 1.c]

·        Master visual alerts should be bright enough to attract the attention of the flightcrew in all ambient light conditions. [AC 25.1322-1, Appendix 1, 1.d(1)]

·        Manual dimming should not be provided unless the minimum setting retains adequate attention-getting qualities when flying under all ambient light conditions. [AC 25.1322-1, Appendix 1, 1.d(2)]

See also: Chapter 2.1 Visual Display Characteristics

·        Design all character types, sizes, fonts, and display backgrounds so that the alerts are legible and understandable at each pilot’s station. These elements should provide suitable attention-getting characteristics. [AC 25.1322-1, Appendix 1, 1.e(1)]

·        We recommend that the alerts subtend at least 1 degree of visual angle. [AC 25.1322-1, Appendix 1, 1.e(2)]

·        Master visual alerts for conditions other than warnings or cautions (for example, Air Traffic Control (ATC) Datalink alerts) must meet the requirements in § 25.1322(f) and follow the guidance in AC 25.1322-1. We recommend using a color other than red, amber, or yellow. [AC 25.1322-1, Appendix 1, 1.f(2)]

Master Auditory Alerts, Annunciations, and Indications

·        The aural alerting must be audible to the flight crew in the worst-case (ambient noise) flight conditions whether or not the flightcrew are wearing headsets (taking into account their noise attenuation and noise canceling characteristics) (§ 25.1322(a)(2)). The aural alerting should not be so loud and intrusive that it interferes with the flightcrew taking the required action. [AC 25.1322-1, Appendix 2, 2.b(1)]

·        The minimum volume achievable by any adjustment (manual or automatic) 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, 2.b(2)]

·        We recommend automatic volume control to maintain an acceptable signal-to-noise ratio. [AC 25.1322-1, Appendix 2, 2.b(3)]

·        To minimize masking, use frequencies different from those that dominate the ambient background noise. [AC 25.1322-1, Appendix 2, 2.a(3)]

·        We do not recommend a master aural alert for advisories because immediate flightcrew attention is not needed for an advisory alert. [AC 25.1322-1, Appendix 2, 2.c(3)]

·        We recommend ramping the onset and offset of any aural alert or unique tone to avoid startling the flightcrew. [AC 25.1322-1, Appendix 2, 2.d(2)]

        (a)   A duration for onsets and offsets of 20-30 milliseconds is acceptable.

        (b)   An onset level of 20-30 decibels above the ambient noise level is acceptable.

·        Use frequencies between 200 and 4500 Hertz for aural signals. [AC 25.1322-1, Appendix 2, 2.a(1)]

·        Each sound should differ from other sounds in more than one dimension (frequency, modulation, sequence, intensity) so that each one is easily distinguishable from the others. [AC 25.1322-1, Appendix 2, 1.b]

·        Aural signals composed of at least two different frequencies, or aural signals composed of only one frequency that contains different characteristics (spacing), are acceptable. [AC 25.1322-1, Appendix 2, 2.a(2)]

·        Signal duration of the master aural alert and unique tones should vary, depending on the alert urgency level and the type of response desired. [AC 25.1322-1, Appendix 2, 2.d(4)]

·        Limit the number of different master aural alerts and unique tones, based on the ability of the flightcrew to readily obtain information from each alert and tone. While different studies have resulted in different answers, in general these studies conclude that the number of unique tones should be less than 10. [AC 25.1322-1, Appendix 2, 2.c(1)]

·        The onset of the master aural alert or unique tone should occur in a timeframe appropriate for the alerting condition and the desired response. Any delays between the onset of the master aural alert or unique tone and its related visual alert should not cause flightcrew distraction or confusion. [AC 25.1322-1, Appendix 2, 2.d(1)]

·        If more than one source of the master aural alert or unique tone is provided, the master aural alert or unique tone for the same condition should occur simultaneously at each pilot’s station. Any timing differences should not be distracting nor should they interfere with identifying the aural alert or unique tone. [AC 25.1322-1, Appendix 2, 2.d(3)]

·        Signal duration of the master aural alert and unique tones should vary, depending on the alert urgency level and the type of response desired. [AC 25.1322-1, Appendix 2, 2.d(4)]

·        Unique tones associated with warnings and cautions should be repeated and non-cancelable if the flightcrew needs continuous awareness that the condition still exists, to support them in taking corrective action. The aural warning requirements listed in §§ 25.1303(c)(1) and 25.729(e) must be followed. [AC 25.1322-1, Appendix 2, 2.d(6)]

·        Unique tones associated with warnings and cautions should be repeated and cancelable by the flightcrew if the flightcrew does not need a continuous aural indication that the condition still exists (for example, Fire Bell or Abnormal Autopilot Disconnect) and if a positive acknowledgement of the alert condition is required. [AC 25.1322-1, Appendix 2, 2.d(7)]

·        Unique tones associated with warnings and cautions should not be repeated if the flightcrew does not need continuous aural indication that the condition still exists. [AC 25.1322-1, Appendix 2, 2.d(8)]

·        Unique tones that are not associated with a warning or a caution (for example, certain advisories, altitude alert, or selective calling (SELCAL)) should be limited in duration. [AC 25.1322-1, Appendix 2, 2.d(9)]

·        Master aural warnings and cautions should be repeated and non-cancelable if the flightcrew needs continuous awareness that the condition still exists, to support the flightcrew in taking corrective action (§ 25.729(e)(2)). The requirements for aural warnings in § 25.729(e) must be followed. [AC 25.1322-1, Appendix 2, 2.d(10)]

·        Master aural warnings and cautions should be repeated until the flightcrew acknowledges the warning condition or the warning condition no longer exists. [AC 25.1322-1, Appendix 2, 2.d(11)]

·        For a time-critical warning, use voice information to indicate conditions that demand immediate flightcrew awareness of a specific condition without further reference to other indications in the flight deck. A second attention-getting sensory cue, such as a visual cue, is still required (§ 25.1322(c)(2)). [AC 25.1322-1, Appendix 2, 3]

Cautions

·        The alert elements used for caution are typically identical to those used for warnings, as both require immediate flight crew awareness. [AC 25.1322-1, 6.d(1)]

·        Some caution alerts are related to conditions that are precursors to potential time-critical warning conditions. In these cases, the alerting system elements associated with the caution should be consistent with the elements for related time-critical warnings. [AC 25.1322-1, 6.d(2)]

·        To ensure the pilot can properly interpret the system status, cautionary annunciation methods should be consistent when numerous interface-switching configurations are possible. [AC 23.1311-1C, 18.2]

·        For caution alerts, if the flightcrew does not need continuous aural indication that the condition still exists, the master aural alert and unique tone should continue through one presentation and then be automatically cancelled. [AC 25.1322-1, Appendix 2, 2.e(1)]

·        If there is any tone associated with an advisory alert, it should be presented once and then be automatically cancelled. [AC 25.1322-1, Appendix 2, 2.e(2)]

·        Provide a means to reactivate canceled aural alerts (for example, the aural alert associated with a gear override). [AC 25.1322-1, Appendix 2, 2.e(3)]

·        When silenced, the aural alerts should be automatically re-armed. However, if there is a clear and unmistakable annunciation in the pilot’s forward field of view that the aural alerts have been silenced, manual re-arming is acceptable. [AC 25.1322-1, Appendix 2, 2.e(4)]

Advisories

·        Functional elements used for advisory alerts do not require immediate flightcrew awareness and are normally provided through a single sense. [AC 25.1322-1, 6]

·        The alerting and informing functional elements for advisories must meet the applicable requirements of § 25.1322 and should include visual information. Advisory information should be located in an area where the flightcrew is expected to periodically scan for information. [AC 25.1322-1, 6.e(1)]

·        Advisory information does not require immediate flightcrew awareness. Therefore, it does not require alerting that uses a combination of two senses. In addition, a master visual or master aural alert is not typically used since immediate flightcrew awareness is not needed. [AC 25.1322-1, 6.e(2)]

·        Aural or visual information such as maintenance messages, information messages, and other status messages associated with conditions that do not require an alert may be presented to the flightcrew, but the presentation of this information should not interfere with the alerting function or its use. [AC 25.1322-1, 6.e(3)] We do not recommend a master aural alert for advisories because immediate flightcrew attention is not needed for an advisory alert. [AC 25.1322-1, Appendix 2, 2.c(3)]

·        The auditory signal should be unique to the operating situation to distinguish between warnings, cautions, and advisories. (MIL-STD-1472G; Garner and Assenmacher, 1997; Smith and Mosier, 1986)

General

·        Aural or visual information such as maintenance messages, information messages, and other status messages associated with conditions that do not require an alert may be presented to the flightcrew, but the presentation of this information should not interfere with the alerting function or its use. [AC 25.1322-1, 6.e(3)]

·        All current messages shall be retrievable. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5.2]

·        For any given message, the entire text should fit within the available space of a single page. This encourages short and concise messages. Additional lines may be used provided the alert message is understandable. [AC 25.1322-1, Appendix 1, 2.b(3)]

        See also: McAnulty, 1995

Message Prioritization

·        Messages should be prioritized and the message prioritization scheme evaluated and documented. [AC 120-76B, 12.k]

        See also: Chandra et al., 2003, 2.4.8

·        Messages should be grouped by urgency level and listed chronologically within each group. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5.2]

        See also: RTCA DO-256, 2.1.7.1 which is worded slightly differently.

·        Within levels of urgency, messages should be displayed in logical order. [AC 25-11A, 31.f(3)(a)]

·        When messages are currently being displayed and there are additional messages in the queue that are not currently displayed, there should be an indication that the additional messages exist. [AC 25-11A, 31.f(3)(a)]

·        An indication shall be provided to identify new messages.  The equipment should also indicate when there are current messages. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5.2]

Message Display and Formatting

·        A text change by itself should not be used as an attention-getting cue (for example, to annunciate mode changes). [AC 25-11A, 31.f(3)(b)]

·        The equipment should provide an indication when additional information (e.g., pages) is available. [TSO-C146c/RTCA DO-229D, 2.2.1.1.4.1]

General

·        Messages from multiple systems should be integrated so that the same information is conveyed.

·        New messages should be distinguished from previous messages.

·        Use short simple sentences. (Smith and Mosier, 1986)

·        Use affirmative statements rather than negative statements. (Smith and Mosier, 1986)

·        When a message describes a sequence of events or steps, the same sequence should be followed in the wording of the message. (Smith and Mosier, 1986)

Message Prioritization

·        A new message should not automatically cover and displace a message currently being displayed. [RTCA DO-256, 2.1.7.1]

Message Queue

·        The message queue display should indicate the number of pending messages. [RTCA DO-256, 2.1.7.1]

·        If all pending messages are not displayed, information shall be provided to notify the pilot of the existence of a queue of these messages. [RTCA DO-256, 2.1.7.1]

Message Display and Formatting

·        Message data shall be available in a directly usable form.  If altitude is required in meters or feet, then both values should be available without requiring the pilot to convert displayed data. [N8110-98]

·        Lines of text shall be broken only at spaces or other natural delimiters. [RTCA DO-256, 2.1.7.2]

·        If the complete message cannot be presented on the same page, there shall be an indicator to the pilot that the message continues. [RTCA DO-256, 2.1.7.2]

·        The message display should present all message text and parameters in a uniform size, font, and style (bold, italics, color) and without emphasis coding of individual data fields upon initial display, to allow flight crew processing and interpretation of the full message content. [RTCA DO-256, 2.1.7.2]

·        If multiple displays are available on the flight deck, consistent formats should be used to present messages on all displays. [RTCA DO-256, 2.1.7.2]

Message Composition and Response

·        If messages require data entry, the system shall provide a preview of all messages as they are composed, and before they are sent by the pilot. [RTCA DO-256, 2.1.7.3]

·        The system shall support editing of pilot‑composed messages to include entry and correction of parameter values in pilot-initiated messages. [RTCA DO-256, 2.1.7.3]

·        For messages that require a pilot response, the system shall indicate the set of appropriate response options, based upon response attribute. [RTCA DO-256, 2.1.7.3]

·        For messages that require a pilot response, the system shall label the set of appropriate response options, e.g., WILCO, UNABLE, STANDBY. [RTCA DO-256, 2.1.7.3]

Message Status

·        An indication shall be provided to identify new messages.  The equipment should also indicate when there are current messages. [TSO-C146c/RTCA DO-229D, 2.2.1.1.5.2]

·        A positive indication shall be presented to depict error and failed message statuses. [RTCA DO-256, 2.1.7.4]

·        The system shall maintain and clearly display message status information to the pilot, including but not limited to whether the message is pending, accepted, or rejected. [RTCA DO-256, 2.1.7.4]

Message History

·        The system shall provide a message history log capability to store, recall, and display messages that were received and sent. [RTCA DO-256, 2.1.7.5]      

·        Displayed history messages shall be distinguishable from pending and open messages. [RTCA DO-256, 2.1.7.5]

·        Message age shall be based on the time that the message was sent. [RTCA DO-256, 2.1.7.5]

·        History log data shall be clearly marked by means of visual coding to prevent the crew from interpreting it as new information. [RTCA DO-256, 2.1.7.5]

Voice/Speech Messages

·        To maintain the effectiveness of voice alerting, the use of voice information as an alert element should be limited. (McAnulty, 1995)

·        Voice messages should be intelligible such that the message is recognized correctly the first time it is heard. (Garner and Assenmacher, 1997)

·        Each voice message should be distinctive in pitch, accent, loudness, etc. (McAnulty, 1995)

·        Voice messages should be presented with monotone inflections to prevent the potentially distracting effects of urgent sounding messages. (Boucek et al., 1980)

·        The speech message should be at least 5 dB above the ambient noise level. (McAnulty, 1995)

·        If voice information is used for multiple functions, an alerting tone should be presented to distinguish a warning message from a routine auditory message. (Stokes, Wickens, and Kite, 1990)

·        Each message should use only words that are familiar to the pilot. Jargon should be avoided. (McAnulty, 1995)

·        Words that rhyme with other words that could be used in the same context and that could lead to misinterpretation should be avoided. (McAnulty, 1995)

·        The phonetic alphabet should be used to present alphanumeric information to discriminate between similar sounding letters, such as “B” and “D” or “M” and “N”. (Garner and Assenmacher, 1997)

·        The speech rate should be approximately 156 words per minute. The speech rate should not be higher than 178 words per minute or less than 123 words per minute. (McAnulty, 1995)

General

·        Using the display selection control position as annunciation is acceptable only under certain conditions. For the flight director, it is acceptable if the control position is appropriately labeled to indicate the function. The control position should be in directview of the pilot and it should be obvious under all lighting conditions. [AC 23.1311-1C, 18.1]

Multiple System Configurations

·        Where multiple system configurations and more than one sensor input are available for source selection, the switching configuration by annunciation or by selector switch position should be readily visible, readable, and should not be misleading to the pilot using the system. Labels for mode and source selection annunciators should be compatible throughout the cockpit. [AC 23.1311-1C, 18.2]

Mode Annunciations

·        When an annunciation is provided for the status or mode of a system, it is recommended that the annunciation indicate the actual state of the system and not just the position or selection of a switch. [AC 25-11A, 31.f(1)(b)]

·        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.

·        Mode changes that are operationally relevant—especially mode reversions and sustained speed protection—should be clearly and positively annunciated to ensure flightcrew awareness. [AC 25.1329-1B, 44.d(1)]

·        The transition from an armed mode to an engaged mode should provide an additional attention–getting feature, such as boxing and flashing on an electronic display (see AC 25-11*) for a suitable, but brief, period (for example, ten seconds) to assist in flightcrew awareness. Aural notification of mode changes should be limited to special considerations. [AC 25.1329-1B, 44.d(2)]

·        In-service experience has shown that mode annunciation alone may be insufficient-unclear or not compelling enough-to communicate mode changes to the flightcrew, especially in high workload situations. Therefore, the safety consequences of the flightcrew not recognizing mode changes should be considered. If necessary, an appropriate alert should be used. [AC 25.1329-1B, 44.d(3)]

·        Mode information provided to the flightcrew should be sufficiently detailed, so that the consequences of the interaction between the FGS and the flightcrew can be determined unambiguously. The FGS interface should provide timely and positive indication when the FGS deviates from the pilot's direct commands (for example, a target altitude or speed setting) or from the pilot's pre-programmed set of commands (for example, waypoint crossing). The interface should also provide clear indication when there is a difference or conflict between pilot-initiated

        commands. An example would be when a pilot engages positive vertical speed and then selects an altitude that is lower than the aircraft altitude. The default action taken by the FGS should be made apparent. [AC 25.1329-1B, 44.d(4)]

·        If information from more than one navigation source can be presented, the selected source should be continuously indicated to the pilot. If multiple sources can be presented simultaneously, the display should indicate unambiguously what information is provided by each source and which one has been selected for guidance. Some airplanes are equipped with an autopilot and/or FD coupled to the lateral and vertical guidance system. On these airplanes, the input to the autopilot and/or FD should coincide with the navigation source selected on the PFD or primary navigational display. [AC 23.1311-1C, 10.2.b]

·        The following design considerations are applicable to operationally relevant system behavior and to the modes of operation of the systems: [AC 25.1302-1, 5-6.c(3)(b)]

        1  The design should be simple.

        2  Mode annunciation should be clear and unambiguous. As an example, a mode engagement or arming selection by the flightcrew should result in annunciation, indication, or display feedback adequate to make the flightcrew aware of the effects of their action. Additionally, any change in the mode as a result of the aircraft’s changing from one operational mode (for instance, on an approach) to another should be clearly and unambiguously annunciated and fed back to the flightcrew.

        3  Methods of mode arming, engagement and de-selection should be accessible and usable. For example, the flightcrew actions necessary to arm, engage, disarm, or disengage an autopilot mode should not be dependent on the mode the system is in. Requiring a different flightcrew action for each mode could contribute to errors. For specific guidance on flight guidance system modes, see AC 25.1329-1B, Approval of Flight Guidance Systems.

        4  Uncommanded mode changes and reversions should have sufficient annunciation, indication, or display information to provide awareness of uncommanded changes of the engaged or armed mode of a system (§ 25.1302(b)(3)).

        5  The current mode should remain identified and displayed at all times.

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

Mode Annunciations

·        If the system has the ability to operate in different modes (e.g., maintenance mode), that system shall continuously indicate what operating mode the system is in. [RTCA DO-256, 2.1.5]

·        The system logon interface shall indicate the type and format of input data expected, including an indication of whether the data fields are mandatory or optional. [RTCA DO-256, 2.1.5]

·        Mode selection or indication of mode annunciations should be clear and unambiguous to prevent mode confusion. (Ahlstrom and Longo, 2003; Palmer et al., 1995)

        See also: Chapter 11 Automation