The only unit information we have is given as 115 Field Regiment RA which was a regiment equipped with field guns that is those guns that were employed to support the infantry in the field as opposed to anti-aircraft, anti-tank, coast or mountain guns among others. As I suggested before, without seeing his record I would be wary of assuming he was on Sheppey with this regiment. I find no evidence of field regiments on Sheppey which did have coast guns and AA guns. The regiment was in the BEF and presumably he, but not the guns, were evacuated from France perhaps at Dunkirk. He could well, as suggested earlier, been re-assigned to another regiment.
There are also problems with the bio information in the Kingston-Bagpuize piece. If he joined the army in 1939, then he re-joined as he had signed on in 1922 (RA Attestation register). He did not get two MIDs (or if he did they aren't both published) - the Dec 1940 LG reference is correct, an MID for "distinguished service in connection with operations in the field Mar-Jun 1940".
Again, as remarked before, apart from the title of this thread, nowhere does the fact that it was an air accident appear, not in the Kingston-B piece, not in the CWGC detail, not on his RA casualty card or in the attestation book. There are, for me at least, too many loose ends and unless the Kent Messenger comes up with something concrete, I would say, again, that without his record then I would prefer to leave speculation to others.
MaxD