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DO-253D Change 1
(i.e., the pilot may be in the middle of doing something else before initiating the function).
An action is defined as a discrete action: e.g., a single button push or a continuous turn of
a knob, even if the knob must be turned multiple times. It is acceptable to exceed the
maximum number of actions, provided the particular actions required are easy to
accomplish and result in a comparable pilot workload (e.g., repeated button pushes of the
Note: Additional information on electronic displays can be found in AC-25-11().
Alert, alarms and symbols shall [LAAS-017] be distinctive and discriminable from one
another. If a control is used to perform multiple functions, the functionality shall [LAAS-
018] be clearly distinguished. There should be a clear indication when any control is in an
altered state and not the default (e.g., if a knob is pulled out and functions differently).
Fields that are editable, selectable, or require operator entry should be clearly denoted.
The equipment should provide an indication when additional information (e.g., pages) is
Brightness, Contrast, and Color
Displays shall [LAAS-019] be readable, and colors shall [LAAS-020] be discriminable
under anticipated lighting conditions. Reflectance of the display should be minimal.
Aviation conventions should be observed when using colors for coding. Color coding of
safety-critical information should be accompanied with another distinguishing
characteristic such as shape or location. No more than five colors should be used on the
display. When color is used to distinguish between functions and indications, red shall
[LAAS-021] not be used other than for warning indications (hazards which may require
immediate corrective action). Amber (yellow) shall [LAAS-022] be reserved for caution
indicators. Blue should be avoided because it is difficult for the human eye to bring blue
symbols into focus and to distinguish the color from yellow when the symbols are small.
(Reference AC 25-11() for generally accepted aviation practices.)
Angle of Regard
All displays shall [LAAS-023] be fully readable up to a horizontal viewing angle of 35
degrees from normal to the face of the display screen. They shall [LAAS-024] be fully
readable up to a vertical viewing angle of 20 degrees from normal to the face of the display
screen. This angle of regard does not ensure that the equipment may be installed in any
aircraft; it is recommended that the angle of regard be maximized to increase the flexibility
of the equipment for installation.
Displays should use characteristics and symbols similar to those shown on published charts
and sectionals or with commonly accepted aviation practices. The potential for
misinterpreting symbols should be minimized. Symbols used for one purpose on published
charts should not be used for another purpose on the equipment display. Guidelines for
electronic display symbology are provided in SAE ARP 4102-7.
Display of letters and numbers depicting primary data shall [LAAS-025] be readable from
viewing distances of 30 inches under anticipated lighting. The required size may depend
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