I would have guessed at something like a Fairchild FDD16ARxxx but their part numbers are FDD16ANxx so I am not sure. It may be somewhere to start though - it is the Fairchild logo. Maybe an obsolete part?
As keith says.
Also if you still cant get anywhere try doing a reverse lookup ...
i.e. Look at what circuit its in - and what it connects to - that should tell you what its doing.
Then do a search for components that do that - a good place to look is the large chip offloading sites
that specialise in obsolete chips. They can often identify old stock.