Mainly bad news as it has turned out that there should have been a record of 348587 between the Airmen's Service Records 1912-1939. As there wasn't, this means that the information was either lost or mistakenly destroyed. It will be much more difficult, if not impossible, to still find out who the person behind the number was.
There is a tiny detail that I, with the help of a specialised acquiantance, now can add though: Further research to the number has shown that although no personal information like regiment, rank or function can be derived from it, we do know that the block of numbers 348587 is part of, was used exclusively for people who enlisted in 1921.