<p>The blade insert body (28) is inserted in a convectional cooling channel (16) of convectional cooling blade of a jet engine and shortens the cross section of the convectional cooling channel. The jet engine is operated with the blade insert body fixed in the convectional cooling channel of the blade. The axial-flow turbo compressor blade or the axial-flow turbine blade are insertable and their convectional cooling channel extends radially.</p>
