The Reserve and Auxiliary Air Forces Act,1952
Section 22. Period of service
Every officer and every enrolled person shall, subject to any rules that may be made in this behalf under this Act, be required to serve in the Auxiliary Air Force for a period of five years from the date of his appointment or enrolment but may, after the completion of his period of service, volunteer to serve therein for further periods each of not more than five years’ duration.