This additional cockpit was fitted with a Scarff ring for a machine gun and carried equipment for air navigation, wireless and gunnery training.

Structurally and aerodynamically, it was almost identical to the Tutor: it had a conventional fabric-covered, metal airframe with single-bay wings.

The usual undercarriage used split, fixed mainwheels and either a tailskid or later a tailwheel, but some 621s appeared on floats and on skis.

Avro employed an aggressive sales and marketing effort to introduce the Model 626 to customers throughout the world.

After demonstrations in Buenos Aires and a record-setting flight over the Andes, the aircraft was commandeered by Argentine military officials to help quell a local uprising.