The aviation side of clearance brings together flying subjects being taken out of the regular catalogue. Older editions turn up here, single boxings left from closed series, and types in scales that see less traffic than 1:72 or 1:48.
Because these are the remains of various lines rather than a planned range, there is nothing systematic about the grouping. The compensation is the chance of finding a type that current catalogues no longer carry at all – which for some builders is the only reason to look at a clearance list.
Before you settle on anything, go through the regular listings in aircraft model kits as well, where subjects are sorted by scale and it is easy to keep a cabinet series consistent. With an older tool, expect a larger share of handwork, so an upgrade from aircraft detail sets is often worth having – etched brass replaces coarse moulded detail and a fresh decal sheet replaces markings that may no longer sit down. The rest of the withdrawn items are in clearance.