The FAA is accepting comments through Sept. 24 on proposed guidance for certifying cockpit controls that include touchscreens, speech recognition and other software-based interfaces. Draft Advisory Circular 20-175A would replace guidance issued in 2011 and applies to aircraft certified under Parts 23, 25, 27 and 29.
The FAA’s underlying approach is largely unchanged from the 2011 guidance, which already addressed issues such as touchscreen usability, hand stabilization and access to frequently used functions. The proposed revision mainly adds more detailed guidance for multi-touch gestures, speech recognition, multimodal controls and newer aircraft configurations such as powered-lift designs.
Voice Commands Get Expanded Guidance
The revision substantially expands the FAA’s treatment of speech recognition, which can allow pilots to control avionics through spoken commands. The agency notes that speech controls could reduce head-down time when a pilot’s hands and eyes are occupied, but recognition can be affected by accents, voice characteristics, stress, fatigue, physical exertion and cockpit noise.
The FAA distinguishes between recognizing spoken words and successfully carrying out a command. As an example, the agency says a system could correctly recognize 93% of spoken words while successfully executing only 65% of commands, illustrating why it considers command-success rate the more useful measure of cockpit usability.
The draft does not establish a specific minimum command-success percentage, but says systems with low success rates should be limited to less-critical functions.
Under the proposed guidance, pilots should have a manual method of controlling functions available when speech recognition is used, and manual controls should take precedence over spoken commands. Speech would not be accepted as the sole means of control. The draft also adds guidance for multimodal interfaces that combine touchscreens, cursor devices and speech recognition, along with a new chapter addressing cockpit controls in emerging aircraft such as powered-lift and eVTOL designs.
Touchscreens Under Turbulence
For touchscreen systems, the FAA says manufacturers should demonstrate acceptable workload, error rates and task-completion times. The guidance calls for support that allows pilots to stabilize their hands while making selections and asks designers to consider turbulence and vibration when developing touchscreen gestures. The FAA recommends limiting gestures to one or two fingers when possible and avoiding gestures that require wrist rotation or more than two fingers.
The draft also addresses the effects of routine cockpit use on touchscreens. Systems should continue operating properly after exposure to skin oils, perspiration, sunlight, cleaners and liquids such as coffee or tea. The FAA also calls for consideration of scratching, hazing and calibration drift. Frequently used and emergency functions should remain readily accessible instead of requiring pilots to navigate through multiple layers of menus.
In practice, the revised guidance would give the FAA more specific criteria for evaluating new cockpit interfaces during certification, including touchscreen usability in turbulence, access to critical functions and manual override of voice commands. It could directly shape how future avionics are designed, tested and approved. The guidance would not require changes to already approved or installed avionics.
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