The airspeed indicator is color coded and marked to denote several key airspeeds on which the pilot routinely relies.

Stall Speed in the Landing Configuration (VSO)

The stall speed in the landing configuration is indicated by the bottom of the white arc on the airspeed indicator.

Stall Speed in a Specified Configuration (VS1)

The stalling speed in a specified configuration (usually clean, meaning flaps and gear retracted) is indicated by the bottom of the green arc on the airspeed indicator.

Maximum Flap Extended Speed (VFE)

The maximum flaps extended speed is indicated by the top of the white arc on the airspeed indicator.

Full Flap Operating Range (White Arc)

The white arc extends from the landing configuration stall speed to the maximum flaps extended speed. You must be in the white arc to use flaps.

Maximum Structural Cruising Speed (VNO)

The maximum structural cruising speed is the speed which should never be exceeded, except when in smooth air, and then only with caution. This speed is indicated on the airspeed indicator as the top of the green arc.

Normal Operating Range (Green Arc)

The green arc on the airspeed indicator shows the normal operating speed range of the airplane. It extends from VS1 to VNO.

Never Exceed Speed (VNE)

The never exceed speed is displayed as a red line on the airspeed indicator. This speed is not to be exceeded under any circumstances.

Smooth Air Operating Range (Yellow Arc)

The yellow arc extends from the maximum structural cruising speed up to the never exceed speed, displaying the smooth air operating range.

Landing Gear Operating (VLO) / Extended (VLE) Speeds

Aircraft with retractable landing gear will have a maximum speed at which the gear may be extended or retracted, VLO. Sometimes VLO is different depending on whether the gear are being raised or lowered. For example, a system with a forward raising nose gear may have a slower VLO for retraction, since the nose gear is fighting the wind to retract forward.

VLE is the maximum speed the airplane may be flown with the gear extended.

These speeds may or may not be marked on the airspeed indicator, depending on the airplane.