Avid at this stage has no direct support for AVCHD.
The AVCHD format is frustrating. It was jointly developed by Sony and Panasonic, but each company's implementation is just different enough so as not to be compatible with the other.
For Panasonic AVCHD there is a tool that Panasonic make available that converts the material to P2 media that Avid can work with. But I don't believe it will work with Sony's version.
Most people using AVCHD now use some third-party tool to convert the footage into something that Avid will support. I can't offer any specific suggestions, but I believe that FFMpeg encoders can provide the necessary support.
In the early days of XDCAM EX people were using FFMpeg to create DNxHD footage from EX clips. A similar process may work for AVCHD - check out this post for a starting point perhaps?
http://www.bolanski.com/ex/home/ffmpeg-is-your-friend/
