25 should not be confusing or ambiguous under any operating ambient illumination conditions. The specific colors should be consistent with change in brightness on the displays over the full range of ambient light conditions. Under high and low levels of lighting, color degradation should not prevent the pilot from properly interpreting display information. Where precipitation is integrated with other information, the precipitation colors can be presented at half intensity. Service experience has shown that this provides enhanced presentation and reduced ambiguity. Warnings should be at full intensity.
9.14.3 Color is an enhancement for understanding the display information that leads to performance improvement, but it should not be the sole means of discrimination of critical information. Color degradation should be obvious and should not preclude the pilot from interpreting the remaining display information. Displays should remain legible, stable, and unambiguous when operating in a degraded mode. The display format should allow the pilot to overlay multiple weather or other graphics relevant to the flight path on one display without ambiguity. Each new graphic should be evaluated both individually and with allowed combinations of other weather, terrain, and navigation symbology to guard against confusing the pilot or cluttering the screen.
9.14.4 For warnings and cautions, § 23.1322 provides specific requirements for the assignment of red and amber for visual annunciations.
9.14.4.1 Red should be used as the warning annunciation for emergency operational conditions when immediate flight crew recognition is required, and immediate correction or compensatory action may be required. Amber should be used for the cautionary annunciation for abnormal operational conditions when immediate flight crew awareness is required and subsequent flight crew action may be required. White or another unique color should be used for advisory annunciations of operational conditions which require flight crew awareness and action may be required. Green should be used for indication of safe operating conditions.
9.14.4.2 A complete list of warnings, cautions, and annunciation messages should be included 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.
9.15 AIRPLANE FLIGHT MANUAL (AFM):
For equipment required for IFR approval, the AFM or supplemental AFM should contain the limitations, and operating and emergency procedures applicable to the equipment installed. Installations limited to VFR use only may require an AFM or supplemental AFM depending upon the complexity of the installation and the need to identify necessary limitation and operating procedures. Additional policy and guidance on AFM's are contained in AC 23-8A.
9.16 LAG TIME AND DATA UPDATE:
The display of information essential to the safety of flight should be thoroughly responsive and accurate to the operational requirements. Electronic display system delay effects of essential information, including attitude, airspeed, altitude, heading, and specific propulsion parameters, should not degrade the pilot's ability to control the airplane. SAE ARP's provide recommended lag times for display of the format and primary flight data, and minimum rates for data updates to meet symbol motion.
9.17 TEST FUNCTIONS:
The electronic display should incorporate a pilot selectable or automatic test mode that exercises the system to a depth appropriate to the system design. Alerting and annunciation functions that are necessary to alert the pilot of unsafe conditions should be exercised.
S/ Michael Gallagher Manager, Small Airplane Directorate Aircraft Certification Service