Airspeed limitations are shown on the airspeed indicator (ASI) by color coding and on placards or graphs in the aircraft. [Figure 8-1] A red line on the ASI shows the airspeed limit beyond which structural damage could occur. This is called the never-exceed speed (VNE). A yellow arc indicates the speed range between maximum structural cruising speed (VNO) and VNE. Operation of an airplane in the yellow airspeed arc is for smooth air only, and then only with caution. A green arc depicts the normal operating speed range, with the upper end at VNO, and the lower end at stalling speed at maximum weight with the landing gear and flaps retracted (VS1). For airplanes the flap operating range is depicted by the white arc, with the upper end at the maximum flap extended speed (VFE), and the lower end at the stalling speed with the landing gear and flaps in the landing configuration (VSO).
Figure 8-1. Single-engine airpseed indicator.
In addition to the markings listed above, small multi-engine airplanes will have a red radial line to indicate single-engine minimum controllable airspeed (VMC). A blue radial line is used to indicate single-engine best rate of climb speed at maximum weight at sea level (VYSE). [Figure 8-2]
Figure 8-2. Multi-engine airpseed indicator.
