The Yellow Arc

Tuesday, November 22, 2022 at 10:52 AM ET

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The two main airspeed presentations found in piston-powered airplanes are shown: a generic “round-dial” airspeed indicator with a prominent yellow arc and a zoomed-in image of a Garmin G1000’s airspeed tape.

Key Takeaways:

The yellow arc (caution range) on a piston aircraft's airspeed indicator signifies a regime of significantly reduced structural protection, certified to withstand only half the gust intensity (15 fps) compared to the green arc.
Flying in the yellow arc is only safe in extremely smooth air with minimal control inputs, as the aircraft can be easily overstressed by turbulence or abrupt maneuvers due to this decreased protection.
VNE (Never-Exceed Speed), the red line at the end of the yellow arc, is the absolute upper limit beyond which even minor control deflections can cause severe structural damage.

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Look at an airspeed indicator or vertical speed tape, as below, in a piston-powered airplane and you’ll see a yellow range of indicated speeds. This is called the “caution range.” Since typical piston airplanes can’t cruise in this speed range under most circumstances, we often don’t spend a lot of time learning how very different the airframe overstress protection scheme is when operating in the yellow arc instead of the green one. It’s not like the FAA decided to spice up airspeed indicators with a splash of color: There is a very real reason for the caution range of the airspeed indicator.