The FAA is warning that pilots are inadvertently changing selections of concentrically centered knobs with some regularity. Citing reports from manufacturers and pilots, the FAA noted that these errors are occurring particularly when pilots dial in comm and nav frequencies. For instance, in one reported incident, rotating the navigation course selection knob resulted in an unintentional change to the barometric altitude setting.

A few examples of common causes of unintentional selections include mechanical interference between two concentrically centered knobs; pilots accidentally rotating two knobs at once as a result of finger positioning errors and/or finger slippage; and pilots inadvertently selecting the wrong knob and subsequently failing to make corrections because they did not detect the error.

To bring attention to this issue and make suggestions to prevent errors, the FAA has published an information for operators letter (InFo 16022) advising pilots, instructors and safety directors of the potential for inadvertently changing correct selections in avionics and other systems with concentrically centered control knobs. “They should collaborate to address that potential in operations and training of flight crews, stressing diligence in operating concentric controls, and in checking for unintentional changes to unrelated systems.”