First, x'must lie close to the transition layer ( i . e ., the region where the number density varies ), otherwise it would mean the attribution of the bulk properties of one of the phase to the surface.
12.
Therefore, aircraft may be flying at both transition level and transition altitude, and still be vertically separated by at least 1, 000 ft . In those areas the transition layer will be 1, 000-1, 500 ft thick, depending on QNH.
