The polishing apparatus has a polishing unit capable of polishing a peripheral portion of the substrate to form a right-angled cross section. The device comprises means for optimizing an approach andor descent profile of an aircraft avoiding long and steep geometric segments, the device to this end inserting an idle segment, if it satisfies the restrictions, in the profile relating to the descent phase andor to the approach phase, wherein said idle segment can be followed by a geometric segment. An existing domestic water supply is supplemented with a dead water storage tank. However, no solvent other than the oil is necessary, a decided improvement over existing technology.