Both .av and .fcf files are used as some sort of documents from Final Draft, so there may be some way to re-save one to another or at least partially convert the data. Sadly, we couldn't really find any relevant information about this particular av to fcf conversion.
Convert Final Draft AV document to Final Draft document file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert av to fcf on Windows
A script writing software for professional writers
Convert from av file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.