The layer of the Earth's atmosphere in which airplanes typically fly is called the stratosphere. The stratosphere begins about 10-12 kilometers above the surface and extends to an altitude of about 50 kilometers. However, the exact altitude range of the stratosphere can vary depending on factors such as latitude and weather conditions. The stratosphere is characterized by relatively stable atmospheric conditions and low levels of turbulence, making it suitable for aviation operations. Commercial airliners typically fly within the lower parts of the stratosphere for efficiency and passenger comfort.