The late model of the BSA airborne bicycle is distinguished by the SINGLE THICK TUBE between the seat and the pedal crank. The seat post slides right inside of it at the top. 

Photo of an unrestored bicycle showing the silver BSA transfer on the seat tube.

There is a BSA transfer (decal) on this single post, about halfway between the seat and pedals, consisting of the BSA trademark of three BSA martini-Henry rifles "piled" (forming a tripod) . The original version appears to be in SILVER, whereas at least one replica version is in gold, with magazines added to the rifles. 

Replica, later design? 

The wing-nuts on the frame appear to be plain without BSA raised letters.

The bracing for the crank consists of two round tubes from just in front, angled back and downwards.

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