Airplanes weighing 12,500 pounds or less, manufactured after 1945, and certificate by the FAA, are required to have airspeed indicators marked in accordance with a standard color-coded marking system. This system of color-coded marking enables a pilot to determine at a glance certain airspeed limitations that are important to the safe operation of the airplane. For example, if during the execution of a maneuver, it is noted that the airspeed needle is in the yellow arc and rapidly approaching the red line, the immediate reaction should be to reduce airspeed.
Airspeed indicators on single engine small airplanes include the following standard color-coded marking:
- White arc—This arc is commonly referred to as the flap operating range since its lower limit represents the full flap stall speed and its upper limit provides the maximum flap speed. Approaches and landings are usually flown at speeds within the white arc.
- Lower limit of white arc (VS0)—The stalling speed or the minimum steady flight speed in the landing configuration. In small airplanes, this is the power-off stall speed at the maximum landing weight in the landing configuration (gear and flaps down).
- Upper limit of the white arc (VFE)—The maximum speed with the flaps extended.
- Green arc—This is the normal operating range of the airplane. Most flying occurs within this range.
- Lower limit of green arc (VS1)—The stalling speed or the minimum steady flight speed obtained in a specified configuration. For most airplanes, this is the power-off stall speed at the maximum takeoff weight in the clean configuration (gear up, if retractable, and flaps up).
- Upper limit of green arc (VNO)—The maximum structural cruising speed. Do not exceed this speed except in smooth air.
- Yellow arc—Caution range. Fly within this range only in smooth air, and then, only with caution.
- Red line (VNE)—Never-exceed speed. Operating above this speed is prohibited since it may result in damage or structural failure.
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