Definition
A system of colored arcs and lines marked on aircraft instrument faces — most commonly the airspeed indicator — that shows the operating ranges and limits the pilot must respect. Each color carries a specific meaning: for example, on the airspeed indicator a green arc indicates the normal operating range, a yellow arc indicates the caution range, a white arc indicates the flap operating range, and a red line marks the never-exceed speed.
Plain English
Colored marks painted on the dial of an instrument that tell the pilot at a glance which speeds or values are safe, which require caution, and which must never be exceeded.
Context Anchor
Seen in the Limitations section when reading about aircraft instrument markings, placards, and operating limits.
Derivation
Color-coding combines “color” with “code,” meaning a system of signs that carries a specific message. In aviation, the color is not just visual decoration; it is part of a code that tells the pilot how to interpret a limit quickly.
Why Pilots Care
Allows rapid recognition of operating limits under high workload, reducing the chance of exceeding aircraft or engine restrictions.
Intuition Check
Color-coding does not mean the colors are just there to make the instrument easier to see. In this context, the colors carry specific operating information the pilot is expected to follow.
Example Sentence 1
The color-coding on the airspeed indicator showed the pilot was flying at the top of the green arc, well within the normal operating range.
Example Sentence 2
Color-coding on the tachometer helped confirm the engine remained inside its normal operating range.