A turbofan with a secondary duct and including a fixed structure and a mobile assembly including a frame with openwork regions. The mobile assembly is translatable between advanced and extended positions. The openwork regions are positioned across the window in the extended position. A plurality of blocking doors is provided, each being mobile between stowed and deployed positions. An array of rams move the mobile assembly. A cascade grille mounts on the frame across the openwork region. The grille slides on the frame parallel to the translational direction. For each grille, a rear stop limits rearward movement, and a compression spring pushes the grille to the rear for abutment against a rear stop. For each grille, the fixed structure comprises a stop element against which the grille abuts upon movement from the advanced position to the extended position.