Originally, all aircraft purchased by the War Office (RFC(MW)) or Admiralty (RFC(NW)/RNAS) had to go through acceptance trials. When production increased the system of sending aircraft to Farnborough etc for testing was not practical, so regional Acceptance Parks were set up to test newly manufactured aircraft prior to their ‘acceptance’ for service use.
The Acceptance Parks required both ‘test pilots’ and ferry pilots, as well as ground staff to erect & disassemble aircraft (which might arrive & leave by rail), re-rig them, introduce minor modifications etc.
Military ‘quality control’ officers were attached to manufacturers as AID inspectors, and so the Acceptance Parks staff would also have to confirm that all the appropriate documentaion was in place.