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You need to create a new post for each plane you have for sale (unless you've done this already) and the assign the category to each of the posts. Each aircraft added in your case will populate the category page however you should be sure to add unique content to the category page. A good way to do this is to add a category description at the top of the category page. If you're using wordpress then I use the 'all in one category updater' to do this. You obviously need to make sure that the category pages can be indexed by Google and then build quality links to the category page from external websites using a mix of brand, partial match keywords, exact match keywords and url links. The key here is natural variation.