All the way back in May 2011, we adopted a new status-rating system for aircraft. So far, only a few have actually been rated, as can be seen in the list 'hockenberry' set up at
Google Docs. If you're an aircraft developer and your aircraft is not on the list, please consider rating their status. All you'll need to know/do is described at
Formalizing Aircraft Status. If you'd just like to get started contributing to FlightGear, this would also seem like an excellent way to get started.