Definition
A yellow band marked on the airspeed indicator that shows the caution range, extending from the maximum structural cruising speed up to the never-exceed speed. Flight within this range is permitted only in smooth air and with caution, because turbulence or abrupt control inputs at these speeds could overstress the airframe.
Plain English
The yellow stripe on the airspeed dial means 'fast, but only in smooth air.' You can fly there, but you have to be careful — bumps or sharp control movements at these speeds can damage the airplane.
Context Anchor
Seen on the airspeed indicator and in airspeed color-code discussions for a specific airplane.
Derivation
Arc comes from a word meaning a bow or curved shape. On a round airspeed indicator, the speed ranges are shown as curved bands, so the yellow arc is the curved yellow band showing the caution range.
Why Pilots Care
Exceeding the lower end of the yellow arc in turbulence can cause structural damage to the aircraft.
Analogy
Think of the yellow arc like a yellow traffic light. It does not always mean stop, but it does mean pay attention and do not treat the situation as normal.
Intuition Check
Do not read yellow arc as simply “fast speed.” In aviation, it specifically means the caution range: smooth air only, and no abrupt control inputs.
Example Sentence 1
As the airspeed climbed into the yellow arc during the descent, the pilot eased back on the throttle to stay clear of the caution range.
Example Sentence 2
In smooth air the aircraft may be flown in the yellow arc, but any turbulence requires an immediate speed reduction.