There is a new digital preview option available for RAF ORB's in AIR27 in the UK National Archives Discovery Database
(AIR27 is operational Squadrons, not OTU's, not training units, not Groups, Wings stations etc, just Squadrons)
I put together a little guide from my experience of using them.
http://www.ww2irishaviation.com/TNA_...guidelines.pdf
They have a text water mark still but I've provided a few examples of what you might find.