Paternal Grandad (who I never knew) was certainly in the RFC and presumably in the RAF in 1918. Must try and find out more...
Several online family history sites boast of having a First Muster database - but charge for it.
I was lucky - about 10 years ago at the AHB doing some squadron research I found this innocuous document, lacking its covers, on a shelf. Found Grandad's details as I knew his service number. Had my camera with me ...