Appendix 1 – Examples for Including Visual System Elements in an Alerting System

ED Decision 2015/019/R

This appendix includes detailed guidance and examples to help applicants with a means of compliance and design for visual system elements in an alerting system. They are based on the Agency’s experience with existing and proposed alerting systems that comply with CS 25.1322. The extent to which this guidance and these examples are applied to a specific type investigation programme will vary, depending on the types of alerts presented, and the level of integration associated with an alerting system. The visual elements of an alerting system typically include a Master visual alert, Visual alert information, and Time-critical warning visual information.

1.       Master Visual

a.       Location. Master visual alerts for Warnings (master warning) and Cautions (master caution) should be located in each pilot’s primary field of view. Appendix 5 of this AMC includes a definition of pilot primary field of view.

b.       Onset/Duration/Cancellation

(1)     The onset of a Master visual alert should occur:

(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).

(2)     The Master visual alert should remain on until it is cancelled either manually by the flight crew, or automatically when the alerting condition no longer exists.

(3)     After the Master visual alert is cancelled the alerting mechanisms should automatically reset to annunciate any subsequent fault condition.

c.       Attention-Getting Visual Characteristics. In addition to colour, 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 synchronised to avoid any unnecessary distraction. AMC 25-11, Electronic Flight Deck Displays, provides additional guidance for using flashing alerts.

d.       Brightness

(1)     Master visual alerts should be bright enough to attract the attention of the flight crew in all ambient light conditions.

(2)     Manual dimming should not be provided unless the minimum setting retains adequate attention-getting qualities when flying under all ambient light conditions.

e.       Display and Indicator Size and Character Dimensions

(1)     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.

(2)     We recommend that the alerts subtend at least 1 degree of visual angle.

f.        Colour

(1)     Standardcolour conventions must be followed for the Master visual alerts (CS 25.1322(d)):

—         Red for Warning

—         Amber or yellow for Caution

(2)     Master visual alerts for conditions other than Warnings or Cautions (for example, Air Traffic Control (ATC) Datalink alerts) must meet the requirements in CS 25.1322(f) and follow the guidance in this AMC. We recommend using a colour other than red, amber, or yellow.

g.       Test function. To comply with the safety requirements of CS 25.1309, include provisions to test/verify the operability of the Master visual alerts.

2.       Visual Information

a.       Quantity and Location of Displays

(1)     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.

(2)     The visual alert information should be located so that both pilots are able to readily identify the alert condition.

(3)     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.

b.       Format and Content

(1)     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 flight crew to the correct checklist procedure, and to minimise the risk of flight crew error.

(2)     The alerting philosophy should describe the format and content for visual information. Use a consistent format and content that includes the following three elements:

—         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)

(3)     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.

(4)     If alerts are presented on a limited display area, use an overflow indication to inform the flight crew that additional alerts may be called up for review. Use indications to show the number and urgency levels of the alerts stored in memory.

(5)     A “Collector message” can be used to resolve problems of insufficient display space, prioritisation 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. The messages that are “collected” (for example, loss of each individual hydraulic system) should be inhibited so the flight crew will only respond to the correct non-normal procedure pertaining to the loss of more than one hydraulic system.

(6)     An alphanumeric font should be of a sufficient thickness and size to be readable when the flight crew are seated at the normal viewing distance from the screen.

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) (See DOD-CM-400-18-05)

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.

Note 3: Different fonts can be used to differentiate between new and previously acknowledged Visual alert information.

c.       Colour. The presentation of Visual alert information must use the following standard colour conventions (§ 25.1322(e)):

—         Red for Warning alerts

—         Amber or yellow for Caution alerts

—         Any colour except red, amber, yellow, or green for Advisory alerts

(1)     Red must be used for indicating non-normal operational or non-normal aircraft system conditions that require immediate flight crew awareness and an immediate action or decision.

(2)     Amber or yellow must be used for indicating non-normal operational or non-normal aircraft system conditions that require immediate flight crew awareness and less urgent subsequent flight crew response (compared to a Warning alert).

(3)     Advisories may use any colour except red or green for indicating non-normal operational or non-normal system conditions that require flight crew awareness and may require subsequent flight crew response.

Note: Use of red, amber, or yellow not related to Caution and Warning alerting functions must be limited to prevent diminishing the attention-getting characteristics of true Warnings and Cautions (CS 25.1322(f)).

d.       Luminance

(1)     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.

(2)     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.

3.       Time-Critical Warning Visual Information

a.       Location. Time-critical warning visual information should appear in each pilot’s primary field of view. Appendix 5 of this AMC includes a definition for pilot primary field of view.

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.

b.       Format

(1)     The corresponding visual and aural alert information should be consistent.

(2)     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).

(3)     Text messages and graphics for Time-critical warning information must be red (CS25.1322(e)(1)(i)). When displaying Time-critical warnings on monochromatic displays, other graphic coding means must be used (CS25.1322(e)).

(4)     The information must be removed when corrective actions (e.g. sink rate has been arrested, aeroplane climbed above terrain, etc.) have been taken, and the alerting condition no longer exists (CS 25.1322(a)(3)).

c.       Size. To immediately attract the attention of the flight crew 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.

4.       Failure Flags. Failure flags indicate failures of displayed parameters or their data source. Failure flags are typically associated with only single instrument displays. The same colours used for displaying flight crew alerts are used for displaying failure flags. In the integrated environment of the flight deck it is appropriate to display instrument failure flags in a colour consistent with the alerting system, as part of the alerting function (see paragraph 5b in the body of this AMC).

[Amdt 25/11]

[Amdt 25/17]