malifox
There is only one Cairnes listed in the Royal Aero Club Aviators (UK)Certificate List dated up to 1926, this is Tom Algar Elliott Cairnes number 1811 dated 2 October 1915.
I would be interested to see what you can find out about "Royal Club for Officers beyond the Seas RAF (1918?" I have never heard of that organization.
His RAF Officers record, providing he did not serve after 1920 will be in The National Archive, Kew, London class AIR76 film 72.
Happy hunting
john_g
66 Squadron