Best wishes with your research and enjoy the forum.
If you have any more information at all, for example, likely period of service with 609 Squadron Royal Auxiliary Air Force, etc that might help.
From his service no, (assuming name and no correct) Samuel A Crichton 1172721 entered the RAFVR (the usual war-time Air Force enlistment being to the Royal Air Force Volunteer Reserve) as an airman, not too long after April 1940 at Cardington - mathematically, perhaps in July 1940. There's a list of Service nos for airmen here
A check at the National Archives of the AIR 78 Index Roll of airmen etc
(as noted here: http://www.rafcommands.com/reference...ervice-number/)
brings up this index list https://discovery.nationalarchives.g...ls/r/C15623934
where image 220 of 290 finds his full name and service no:
Samuel Arthur Crichton 1172721
It appears, from a search of the London Gazette online (https://www.thegazette.co.uk/), that he served in the RAFVR throughout as an airman or NCO (had he been commissioned, there would be a Gazette notification showing his appointment from the ranks, with that service no, to Officer -Pilot Officer on probation, most likely- with new service no).
609 Squadron was based at Biggin Hill for several periods, roughly Feb-Jul 41, Sep-Nov 41, Sep 42 -Nov 42.
At UK National Archives, digitised images of RAF Squadron Operations Record Books, both the Form 540 Summary of Events and Form 541 Record of Events, compiled monthly, are available to view or download, no charge at present. It is possible that he may be shown there, if aircrew/pilot, most likely in the Form 541s
See 609 Squadron Operations Record Book pages listing here:
If you are next of kin, or have next of kin permission, you can reqest a copy of his RAF Record of Service, the double-sided A3 Form 543, at a cost of 30 pounds.
Very condensed, sometimes sparse, sometimes much fascinating detail - which you may need further help to unravel the acronyms etc.
Follow the notes and forms details as shown here:
An alternative is to ask the 609 Squadron Association, site here: