US Army Air Service question

Recently I have been doing some research on my great-grandfather, since my family has recently rediscovered his WWI uniform. I know from the patches that he was a First Sergeant in the Army Air Service. He seems to have two 6 months overseas service patches also. He also has the honorable discharge patch. However this is just about all I can find. From what I have researched, I know he wasn't a pilot, but I am wondering what he may have done as a First Sergeant. I have been unable to find any information on it so far, if anyone could tell me or point me in the right direction, it would be very appreciated.

edit:If this is in the wrong forum, I apologize, as I can see how it might also go under uniforms : /