MIL-STD-411F
should be flight phase related, that is, non-critical messages should be inhibited during critical phases of flight, during high workload periods, and during multiple failure situations. Any specific methodology for applying an inhibit logic shall be evaluated and approved by the acquiring
activity prior to implementation (see 6.3.1).
5.2.6.3 Storage and recall. If specified by the acquiring activity, a capability shall be provided to enable the crew to store and recall caution and advisory level messages. The display shall provide an indication of the quantity and type of messages that are in memory. Both selective and total storage and recall capabilities should be provided.
5.2.7 Display luminance and contrast. Displays shall be in accordance with
MIL-STD-1472. For monochrome displays, luminance and contrast shall be in accordance with
the system specification and shall be such that alert messages are easily readable from the design
eye position (see 3.8) in any ambient light condition. The minimum display luminance shall not be
less than 1.5 fL to prevent the dimming of the display to such a level that would make the alert
message unreadable. For color displays luminance contrast shall be in accordance with the system
specification and shall ensure the discriminability of the alert message from the background.
5.2.8 Display size. Specific aircraft design characteristics shall determine the minimum number of message lines to be displayed, allowing for the need to have characters large enough to be legible to crewmembers seated in their normal flight positions. If legends are abbreviated, the display shall be wide enough so that any message will fit on one line.
5.2.9 Character dimensions. The alphanumeric character dimensions and spacing shall be selected for speed and accuracy of interpretation and shall be in accordance with MIL-STD-1472. The height of symbols and characters shall subtend a viewing angle of no less than 20 minutes of arc when measured from the design eye position (see 3.8). Character dimensions and fonts shall be evaluated and approved by the acquiring activity before implementation (see 6.3.1).
5.2.10 Maintenance record. A capability shall be provided to have all warning and caution messages recorded in non-volatile memory for maintenance purposes. None of the advisory messages shall be stored for maintenance purposes. Because several warning and caution conditions will normally be present before the start of the engine, the storage of warning and caution conditions in a non-volatile memory shall be inhibited while the "on ground" conditions exist. If any of these conditions are still present when the "on ground" condition no longer exists, they shall be recorded in non-volatile memory for maintenance records. The memory shall be capable of being cleared by maintenance personnel when the existing record is no longer required.
5.2.11 Test provisions. A convenient means shall be provided for testing all integrated display characters and functions.
5.3 Audio warning signals. Audio warning signals, when used, shall conform to the requirements specified herein and to the audio display requirements of MIL-STD-1472.
5.3.1 Master warning signals. A nonverbal audio master warning signal shall produce an output with the following frequency and interruption rates:
a. Fundamental audio output frequency shall sweep from 700 to 1,700 Hz in 0.85 seconds. b. Interruption interval shall be 0.12 seconds.
The cycle shall be repeated until the signal generator is deenergized.
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