Definition
Colored arcs, lines, and bands painted on the face of an aircraft instrument that show the operating limits and recommended ranges for the value being measured. Standard markings include a red line for never-exceed or do-not-operate limits, a green arc for the normal operating range, a yellow arc for the caution range (operate only in smooth conditions), and a blue or white arc for special ranges such as flap operating speeds or single-engine performance.
Plain English
Colored marks on a gauge that tell the pilot at a glance whether the reading is safe, cautionary, or off-limits.
Context Anchor
Seen on cockpit instruments such as airspeed, engine speed, temperature, and pressure gauges, and checked during inspections or instrument replacement.
Derivation
"Range" here means a span between two limits, and "markings" are the painted indicators showing those limits. The combination tells the pilot the boundaries of safe operation directly on the instrument face.
Why Pilots Care
They provide instant visual confirmation that an engine or flight parameter is within safe limits, reducing the chance of exceeding structural or performance limits during flight.
Analogy
Like the green-yellow-red zones on a car temperature gauge that show normal, warming, and overheating at a glance.
Intuition Check
Do not read “range” here as distance. In this term, “range” means a span of allowed or unsafe values on a gauge, and “markings” are the visible colors or lines that show those spans.
Example Sentence 1
During the runup, the mechanic checked that the oil pressure needle settled into the green arc on the gauge.
Example Sentence 2
During the preflight inspection the mechanic verified that the tachometer range markings matched the engine limitations listed in the aircraft flight manual.