The Avro 548 was a civil trainer aircraft built in Britain after World War I. Its design was based extensively on Avro's 504 military aircraft, but it had an inline engine and a third seat. The prototype, designated 545, first flew with a Curtiss OX-5 V-8 engine, but this proved impractical for the civil market on account of the engine's weight and the complexity of its cooling system. An air-cooled Renault engine was used instead, and the designation 548 applied to this configuration. In practice, these aircraft were usually customised for their buyers and most differed from each other in equipment and detail; some were actually retrofitted war-surplus 504s. Many were used as civil trainers, others for joyriding, personal transport, or racing.