At what altitude do passenger planes usually and maximally fly?
Answer from: Andrey Kudryavtsev:
A secret agent in His Majesty's service....
Normally, civil airliners fly at an altitude of 9 to 12 kilometers.
For example, the maximum flight altitude of the Boeing 737 (the most popular passenger aircraft) is 10,670 to 12,500 meters, depending on version.
Answer from: Julian Avramov:
Psychologist, wife, mother...
The altitude of the flight is determined economically. the higher, the lower the air density and the less drag, but the more rarefied the air, the less lift = mass of the aircraft. Therefore, the most advantageous flight altitude is calculated. At the beginning of the flight, when the airplane is heavier because of full tanks, the altitude will be lower. This is what was explained at the aviation institute.