The HR.100 first flew in April 1969, and is in essence a development of the DR.253 Regent with metal construction. The first production variant was the HR.100/180 with the 134-kW (180-hp) Avco Lycoming O-360, but this was soon replaced by the HR.100/200. In 1971 Avions Pierre Robin placed in production its first all-metal aircraft, the HR 100/200, designed by M Christophe Heintz. The HR.100/320/4+2 up-engined variant for two children as well as four adults failed to progress past the prototype stage, so the next model was the HR.100/ 210 with a 157-kW (210-hp) engine. At this stage retractable landing gear and Continental engines entered the picture to produce the HR.100/285 with the 239-kW (285-hp) Tiara: this model entered production with the Tiara 6-285B version of the engine. This basic model was also produced in the HR.100/250TR version with the 186-kW (250-hp) Avco Lycoming IO-540 engine.