The present invention relates to a turbine engine having a casing (7) which has an inner wall (3i) forming a wall of an air duct (3) and at least one opening (7r) passing through the casing, leading into the duct (3) and forming a passage for an endoscope. The opening (7r) is closed during operation of the turbine engine by a stopper (8) which has an end-surface portion (8s) in the extension of the inner wall (3i). An indicator of wear to the inner wall of the casing is associated with the stopper (8) or with the inner wall (3i) of the casing, in the proximity of the stopper (8).