what does the lower limit of the green arc on an airspeed indicator represent
Airspeed indicator A redline mark indicates VNE, or velocity (never exceed). This is the maximum demonstrated safe airspeed that the aircraft must not exceed under any circumstances. The red line is preceded by a yellow band which is the caution area, which runs from VNO (maximum structural cruise speed) to VNE. A green band runs from VS1 to VNO. VS1 is the stall speed with flaps and landing gear retracted. A white band runs from VSO to VFE. VSO is the stall speed with flaps extended, and VFE is the highest speed at which flaps can be extended. Airspeed indicators in multi-engine aircraft show a short radial red line near to the bottom of green arc for Vmc, the minimum indicated airspeed at which the aircraft can be controlled with the critical engine inoperative and a blue line for VYSE, the speed for best rate of climb with the critical engine inoperative.