Step-by-step explanation:
Mostly the commercial flights fly at the altitude of 10 -12 km .
The range is in between the upper most part of the troposphere to the lower part of the stratosphere .
Since ,
At this height ,
The air is dense enough to generate the sufficient lift .
Since , the lift is generated due to the difference in the pressure of air , between the top and the bottom of the wing .
As we go beyond 15 km , where the ozone layer is present , the pressure of sir reduces at this altitude ,
And , the plane are not able to fly at this , as ,
the lift is not generated , due to reduced air pressure .