After learning to fly with the RAF Volunteer Reserve and training at the de Havilland Technical School, Pat Fillingham joined de Havilland as a test pilot in 1939. He spent much of the early part of the War carrying out production test flights of Tiger Moth biplane trainers, including those produced at the Morris Motors works in Cowley, Oxford. He rose to become chief production test pilot and his 2200 Mosquito flights is believed to be a record.
Post War, Fillingham was busy flying all de Havilland products including the Dove, Mosquito and Vampire. On 22 May 1946, he carried out the first flight of the Chipmunk from Downsview, Canada. On 26 August 1949, he carried out the first flight of the first British-built Chipmunk, WB549, displaying it at the SBAC show at Farnborough just over a week later. Flying another Chipmunk, he was British Air Racing Champion in 1952 and winner of the King’s Cup in 1953.
Fillingham went on to test fly the Comet and Trident jet airliners, retiring as Deputy Chief Test Pilot of Hawker Siddeley Aviation in 1975.