The signal manufacturer says the sky is very large, but the modern plane is very fast, so there is still a danger of collision. To avoid air collision accident, in addition to regular flights of civil aviation aircraft provided certain routes, the pilot in the air at the same time also must pay attention to observe situation around. Around the observation plane, in order to facilitate the pilot know how other aircraft relationship with their course at any time, so at the time of night, will open at the end of the both side of the plane and the three navigation lights, from the point of the position of the pilot, the red light is always on the left wing tip, green light on the right wing tip, white light is installed in the tail. Three lamps can be lit continuously, and can be lighted.

After the night flight turned on the navigation lights, the pilot was able to observe the situation. If the pilot saw a plane on the same height with yourself, and only see two lights are red, green, it shows that the other party is approaching, there is a risk of collision, must try to avoid. If you see a light, you are on your left or right. If the three lights are visible at the same time, it means that the other person is flying above or below their own, which is not dangerous.