The red line on an airspeed indicator indicates the maximum speed at which the airplane can be operated in smooth air, which should never be exceeded intentionally. This speed is known as the never-exceed speed.
The numbers are in meters. If the plane is below 100 meters in altitude, the trail will be white. If it is above 100 meters, the trail will yellow, then green, then above 2500 meters it will become light blue, then dark blue, purple and for the highest altitude it will be red. I hope this helps.Most commercial airplanes have a green light on one of their wings and a red light on the opposite wing. The red light is located on the airplane's left wing, whereas the green light is located on the airplane's right wing.
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