Question

in which layer of the atmosphere jet plane flies

Answer 1

Most planes fly in the layer of atmosphere found nearest or closest to the earth i.e. the Troposphere. Larger planes though are found flying in the upper part of the troposphere, the Tropopause or the lower part of the stratosphere as this layer keeps them saved from disturbances owing to weather conditions.

Answer 2

Commercial jet aircrafts, typically fly at altitudes of 36000 feet to 41000 feet. That is, they fly in the lower level of Stratosphere and also in the top level of the Tropopause. One exception is the Concorde, which flew at altitudes of 60000 feet as it cruised at 1350mph speed.