Seconding what jjk said, also airliners cruise in the troposphere, not the stratosphere. > From the planetary surface of the Earth, the average height of the t

Seconding what jjk said, also airliners cruise in the troposphere, not the stratosphere. > From the planetary surface of the Earth, the average height of the troposphere is 18 km (11 mi; 59,000 ft) in the tropics; 17 km (11 mi; 56,000 ft) in the middle latitudes; and 6 km (3.7 mi; 20,000 ft) in the high latitudes of the polar regions in winter; thus the average height of the troposphere is 13 km (8.1 mi; 43,000 ft). Airliners cruise around flight level 310-380 (31-38,000', about 5.9 to 7.2 miles).