I believe this is the rank of "flight sergeant" when they were re-designated as Aircrew 1 and was used between July 1 1946 and 1950. Here is a description from wikipedia - the source of all true knowledge ;-)
http://en.wikipedia.org/wiki/Flight_sergeant
"On 1 July 1946, aircrew flight sergeants were redesignated Aircrew I and replaced their chevrons with
three six-pointed stars within a wreath and surmounted by an eagle and a crown. This proved unpopular however, and in 1950 they reverted to their old rank and badge, although Flight Sergeants Aircrew wear an eagle between chevrons and crown. Flight Sergeants in ground trades wear only a crown above the three chevrons."