The design was developed around the 67kW R.A.F.1A engine, of which war surplus supplies were available at knockdown prices. First flown in July 1924 by Geoffrey de Havilland, the D.H.51 (G-EBIM) proved to be satisfactory, but since the engine did not have dual ignition a Certificate of Airworthiness was refused. Ten hours of airborne testing would have been required with the single-ignition RAF1A, but de Havilland decided that the cost of this was not justified.

 

It was decided to re-engine the D.H.51 with an Airdisco engine by October 1924 and this move, although conferring considerably enhanced performance, took the aircraft well outside the economic operating bracket for which it was designed. Within a short time it had been fitted with new shorter span wings with automatic flaps to become the sole DH51A.

As a result, only three were built; the first being written-off in 1931 and scrapped in 1933 respectively, G-EBIM.

 

The second was G-EBIQ.

 

 

The third, G-EBIR c/n 102, built in 1925 and shipped to Kenya in early 1926, became the first aircraft on that country's civil register. It was registered G-KAA in September 1928 and VP-KAA in January 1929. Dismantled during the war, and airfreighted to the UK in 1965, it survived to fly again and now, after several rebuilds, is again back in the UK, maintained by the Shuttleworth Trust at Old Warden as the oldest airworthy design of the de Havilland Aircraft Company.