What is the main risk indicated by the yellow arc on an airspeed indicator?

The yellow arc on an airspeed indicator signifies the airspeed range where the aircraft is operating in a potentially unsafe speed range. This range is generally known as the caution or cautionary zone. Within this zone, pilots should exercise caution as the aircraft may not respond predictably or may be approaching the limits of safe performance, particularly in turbulent conditions or during maneuvers.

Understanding that the yellow arc indicates a warning for the pilot is crucial for maintaining safe flight operations. By recognizing this warning, pilots are encouraged to avoid operating within this range unless necessary and to only do so with great care for the risk of stalling or losing control. This arc serves as a visual cue to remind pilots to keep their speeds within a more favorable range for safe flight.

In contrast, other options refer to specific flight concerns: stalling is specifically indicated by the lower red radial, maximum flap extension speed is defined by the upper limit of the white arc, and loss of altitude control may relate to various flight conditions but is not directly indicated by the yellow arc. Each of these represents important considerations, but the yellow arc specifically addresses the broader risk associated with operating in a cautionary airspeed range.