From this page
Nationality and residency - RAF Careers
"
Nationality
The nationality requirements for each job are given in each of the job files on this website.
To apply for any RAF job, you must be a citizen of the UK or the Republic of Ireland, or have been a Commonwealth citizen since birth, or hold dual UK/other nationality.
For security reasons, there are stricter nationality requirements for some jobs. For a few, you must have been a UK citizen and UK resident since birth.
Residency
You must have lived in the UK for the five years immediately before you apply to join. For a few jobs, the qualifying period is 10 years."
Given that the RAF has plenty of UK residents applying, I'd have to wonder whether they'd bother for long with someone who does not meet the residency rules.