For a short period of time in 1918, the rank bars were worn on the caps for ranks 2nd Lieutenant, Lieut. and Captain as a result of AMWO 617/18 and Air Force Memorandum 2. The bars on my example could indicate that but I'm not sure if the style of cap badge crown dates to 1918. It would be great to see any other cap badge that matches the example in the initial post.
Th band rank bars have been discussed in an earlier post in the Forum:
http://www.britishbadgeforum.com/for...highlight=1918
Regards