  I had the same problem awhile back: I added an external links section with the IMPDB and it was undone immediately thereafter under the external links rules, but I feel that's a complete misinterpretation of the guidelines. The rule (or rules if you include both 4 and 12) is/are intended to keep things clean by not linking to pathetic wikis with lotsa vandalism and/or blatant spam. The IMPDB is neither, having been fairly stable, well organized, and growing at a considerable rate (several articles per week). It's still new, but based on the firearms database and quite well done. A link to the planes database is really no different than all the many links to Wookiepedia, Memory Alpha, and the Muppet wiki among others, albeit on a smaller scale. Continually denying this external link simply prevents this article from having a solid external resource, and, I would add, is a bit hypocritical. (Anything goes here, but lets not direct readers to a well done site?!)