 He was later chief flying instructor for the Vickers Wellington and he was a member of the inaugural class at the Empire Test Pilots' School at RAF Boscombe Down.Hazelden left the RAF in 1947 and he was appointed as the chief test pilot of Handley Page.Notably, he carried out the flight test development of the Hastings military transport, the Victor four-jet nuclear weapon carrying V bomber (and later tanker aircraft), and the Hermes and Dart Herald airliners.