I can only tell you about my experiences with the Tamron 28-300 which I am currently selling on Ebay, since I'm buying a 70-200L f4. If you want to use it exclusively for aviation photography then I don't know if it is the right lens for you, because past 200mm it tends to be rather soft in my opinion. Feel free to check out my photos and see what results you are able to get with this lens.
If you want to get it for all kinds of photography and you don't really want to make big prints of the things you take pictures of beyond 200mm then I can recommend it, since 28-300 is pretty cool, since you don't have to switch lenses all the time, and it definitely does the job for everyday photography or for vacation and alike. Feel free to contact me, if further questions arise.