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DO-253D Change 1
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operation of controls should be consistent with the principles and specifics presented in the
Accessibility of Controls
Controls that are normally adjusted in flight shall [LAAS-006] be accessible without
interfering with the visibility of critical displays. Controls shall [LAAS-007] provide clear
tactile or visual feedback when operated. The controls shall [LAAS-008] be movable
without excessive effort and detents shall [LAAS-009] be well defined. Control spacing,
physical size, and control logic shall [LAAS-010] be sufficient to avoid inadvertent
activation. Controls shall [LAAS-011] be operable with the use of only one hand.
Controls that do not require adjustment during flight shall [LAAS-012] not be readily
accessible to flight personnel.
Labels shall [LAAS-013] be readable from viewing distances of 30 inches, under
anticipated lighting conditions. Labels should be unobstructed by controls when viewed
within the angle of regard, and located next to or on the controls that they reference. Label
placement should follow a consistent logic. Terminology for labeling should describe the
function of the control in meaningful terms. Terms should be consistent with those on the
display of the function or mode selected and spelled out whenever possible.
Equipment Operating Procedures
Equipment operating procedures should be designed to maximize operational suitability,
minimize pilot workload, and minimize reliance on pilot memory. Detectability of
operating errors should be maximized. The actions required to recover from errors should
be intuitive, quick, and with minimum impact on subsequent operations. Where possible,
maximum use of prompting should be used to minimize reliance on pilot memory.
Operating rules and use of controls required to implement equipment functions should be
consistent from mode to mode.
Use of prompting cues shall [LAAS-014] be consistent. For example, if used as such a cue,
illumination of controls would always indicate that the illuminated control should be used
Minimum Workload Functions
Operations that occur regularly or are conducted under potentially stressful operating
conditions (e.g., missed approaches) must be possible with a small number of control
operations. The number of operations may be minimized through the use of dedicated
controls, anticipation of pilot requirements, and the use of quick-access menus designed to
facilitate rapid selection of required navigation functions (e.g., direct flight to a waypoint
and returning to the final approach course after a missed approach). During flight, selection
or activation of a function shall [LAAS-015] not require simultaneous use of two or more
controls (e.g., pushing two buttons at once). If a keypad is included in the design, it should
permit single-handed data entry with a layout that enhances both the accuracy and speed
of data input. Where multiple actions are necessary to accomplish a function, the
equipment should provide contextual information of the active sub-function or mode (e.g.,
The task of selecting an approach (reference Section 2.3.4) shall [LAAS-016] be capable
of being accomplished within the recommended maximum number of five actions and with
less than 10 seconds to accomplish the task (as a bench test without distraction). Both the
time and number of actions are worst-case, regardless of where the function is initiated
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